/usr/share/doc/kea-doc/html/kea-guide.html is in kea-doc 1.0.0-1build1.
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name="description" content="Kea is an open source implementation of the Dynamic Host Configuration Protocol (DHCP) servers, developed and maintained by Internet Systems Consortium (ISC). This is the reference guide for Kea version 1.0.0. The most up-to-date version of this document (in PDF, HTML, and plain text formats), along with other documents for Kea, can be found at ."></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book"><div class="titlepage"><div><div><h1 class="title"><a name="idm6279648"></a>
Kea Administrator Reference Manual
<span class="inlinemediaobject"><img src="kea-logo-100x70.png" align="left"></span>
</h1></div><div><p class="releaseinfo">This is the reference guide for Kea version
1.0.0.</p></div><div><p class="copyright">Copyright © 2010-2015 Internet Systems Consortium, Inc.</p></div><div><div class="abstract"><p class="title"><b>Abstract</b></p><p>
Kea is an open source implementation of the Dynamic Host Configuration
Protocol (DHCP) servers, developed and maintained by Internet Systems
Consortium (ISC).
</p><p>
This is the reference guide for Kea version 1.0.0.
The most up-to-date version of this document (in PDF, HTML,
and plain text formats), along with other documents for
Kea, can be found at <a class="ulink" href="http://kea.isc.org/docs" target="_top">http://kea.isc.org/docs</a>.
</p></div></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="chapter"><a href="#intro">1. Introduction</a></span></dt><dd><dl><dt><span class="section"><a href="#idp50568016">1.1. Supported Platforms</a></span></dt><dt><span class="section"><a href="#required-software">1.2. Required Software at Run-time</a></span></dt><dt><span class="section"><a href="#kea_software">1.3. Kea Software</a></span></dt></dl></dd><dt><span class="chapter"><a href="#quickstart">2. Quick start</a></span></dt><dd><dl><dt><span class="section"><a href="#quick-start">2.1. Quick start guide for DHCPv4 and DHCPv6 services</a></span></dt><dt><span class="section"><a href="#quick-start-direct-run">2.2. Running Kea servers directly</a></span></dt></dl></dd><dt><span class="chapter"><a href="#installation">3. Installation</a></span></dt><dd><dl><dt><span class="section"><a href="#packages">3.1. Packages</a></span></dt><dt><span class="section"><a href="#install-hierarchy">3.2. Install Hierarchy</a></span></dt><dt><span class="section"><a href="#build-requirements">3.3. Building Requirements</a></span></dt><dt><span class="section"><a href="#install">3.4. Installation from Source</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54877744">3.4.1. Download Tar File</a></span></dt><dt><span class="section"><a href="#idp54879728">3.4.2. Retrieve from Git</a></span></dt><dt><span class="section"><a href="#configure">3.4.3. Configure before the build</a></span></dt><dt><span class="section"><a href="#idp51819024">3.4.4. Build</a></span></dt><dt><span class="section"><a href="#idp51821792">3.4.5. Install</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp-config-backend">3.5. Selecting the Configuration Backend</a></span></dt><dt><span class="section"><a href="#dhcp-install-configure">3.6. DHCP Database Installation and Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp51839952">3.6.1. Building with MySQL Support</a></span></dt><dt><span class="section"><a href="#idp51846720">3.6.2. Building with PostgreSQL support</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#admin">4. Kea Database Administration</a></span></dt><dd><dl><dt><span class="section"><a href="#kea-database-version">4.1. Databases and Database Version Numbers</a></span></dt><dt><span class="section"><a href="#kea-admin">4.2. The kea-admin Tool</a></span></dt><dt><span class="section"><a href="#idp54116336">4.3. Supported Databases</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54117072">4.3.1. memfile</a></span></dt><dt><span class="section"><a href="#idp53820304">4.3.2. MySQL</a></span></dt><dt><span class="section"><a href="#idp51946336">4.3.3. PostgreSQL</a></span></dt><dt><span class="section"><a href="#idp51986896">4.3.4. Limitations related to the use of the SQL databases</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#kea-config">5. Kea configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#json-backend">5.1. JSON configuration backend</a></span></dt><dd><dl><dt><span class="section"><a href="#json-format">5.1.1. JSON syntax</a></span></dt><dt><span class="section"><a href="#idp53045488">5.1.2. Simplified Notation</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#keactrl">6. Managing Kea with keactrl</a></span></dt><dd><dl><dt><span class="section"><a href="#keactrl-overview">6.1. Overview</a></span></dt><dt><span class="section"><a href="#keactrl-usage">6.2. Command Line Options</a></span></dt><dt><span class="section"><a href="#keactrl-config-file">6.3. The keactrl Configuration File</a></span></dt><dt><span class="section"><a href="#keactrl-commands">6.4. Commands</a></span></dt><dt><span class="section"><a href="#keactrl-overriding-servers">6.5. Overriding the Server Selection</a></span></dt></dl></dd><dt><span class="chapter"><a href="#dhcp4">7. The DHCPv4 Server</a></span></dt><dd><dl><dt><span class="section"><a href="#dhcp4-start-stop">7.1. Starting and Stopping the DHCPv4 Server</a></span></dt><dt><span class="section"><a href="#dhcp4-configuration">7.2. DHCPv4 Server Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54262112">7.2.1. Introduction</a></span></dt><dt><span class="section"><a href="#idp54498048">7.2.2. Lease Storage</a></span></dt><dt><span class="section"><a href="#idp54960688">7.2.3. Hosts Storage</a></span></dt><dt><span class="section"><a href="#dhcp4-interface-configuration">7.2.4. Interface configuration</a></span></dt><dt><span class="section"><a href="#dhcpinform-unicast-issues">7.2.5. Issues with unicast responses to DHCPINFORM</a></span></dt><dt><span class="section"><a href="#ipv4-subnet-id">7.2.6. IPv4 Subnet Identifier</a></span></dt><dt><span class="section"><a href="#dhcp4-address-config">7.2.7. Configuration of IPv4 Address Pools</a></span></dt><dt><span class="section"><a href="#dhcp4-std-options">7.2.8. Standard DHCPv4 options</a></span></dt><dt><span class="section"><a href="#dhcp4-custom-options">7.2.9. Custom DHCPv4 options</a></span></dt><dt><span class="section"><a href="#dhcp4-vendor-opts">7.2.10. DHCPv4 Vendor Specific Options</a></span></dt><dt><span class="section"><a href="#dhcp4-option-spaces">7.2.11. Nested DHCPv4 Options (Custom Option Spaces)</a></span></dt><dt><span class="section"><a href="#dhcp4-option-data-defaults">7.2.12. Unspecified parameters for DHCPv4 option configuration</a></span></dt><dt><span class="section"><a href="#dhcp4-stateless-configuration">7.2.13. Stateless Configuration of DHCPv4 clients</a></span></dt><dt><span class="section"><a href="#dhcp4-client-classifier">7.2.14. Client Classification in DHCPv4</a></span></dt><dt><span class="section"><a href="#dhcp4-ddns-config">7.2.15. Configuring DHCPv4 for DDNS</a></span></dt><dt><span class="section"><a href="#dhcp4-next-server">7.2.16. Next Server (siaddr)</a></span></dt><dt><span class="section"><a href="#dhcp4-echo-client-id">7.2.17. Echoing Client-ID (RFC 6842)</a></span></dt><dt><span class="section"><a href="#dhcp4-match-client-id">7.2.18. Using Client Identifier and Hardware Address</a></span></dt></dl></dd><dt><span class="section"><a href="#host-reservation-v4">7.3. Host reservation in DHCPv4</a></span></dt><dd><dl><dt><span class="section"><a href="#reservation4-types">7.3.1. Address reservation types</a></span></dt><dt><span class="section"><a href="#reservation4-conflict">7.3.2. Conflicts in DHCPv4 reservations</a></span></dt><dt><span class="section"><a href="#reservation4-hostname">7.3.3. Reserving a hostname</a></span></dt><dt><span class="section"><a href="#reservation4-options">7.3.4. Reserving specific options</a></span></dt><dt><span class="section"><a href="#reservation4-mode">7.3.5. Fine Tuning IPv4 Host Reservation</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp4-serverid">7.4. Server Identifier in DHCPv4</a></span></dt><dt><span class="section"><a href="#dhcp4-subnet-selection">7.5. How the DHCPv4 Server Selects a Subnet for the Client</a></span></dt><dd><dl><dt><span class="section"><a href="#dhcp4-relay-override">7.5.1. Using a Specific Relay Agent for a Subnet</a></span></dt><dt><span class="section"><a href="#dhcp4-srv-example-client-class-relay">7.5.2. Segregating IPv4 Clients in a Cable Network</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp4-decline">7.6. Duplicate Addresses (DHCPDECLINE support)</a></span></dt><dt><span class="section"><a href="#dhcp4-stats">7.7. Statistics in DHCPv4 server</a></span></dt><dt><span class="section"><a href="#dhcp4-ctrl-channel">7.8. Management API for the DHCPv4 server</a></span></dt><dt><span class="section"><a href="#dhcp4-std">7.9. Supported DHCP Standards</a></span></dt><dt><span class="section"><a href="#dhcp4-limit">7.10. DHCPv4 Server Limitations</a></span></dt></dl></dd><dt><span class="chapter"><a href="#dhcp6">8. The DHCPv6 Server</a></span></dt><dd><dl><dt><span class="section"><a href="#dhcp6-start-stop">8.1. Starting and Stopping the DHCPv6 Server</a></span></dt><dt><span class="section"><a href="#dhcp6-configuration">8.2. DHCPv6 Server Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp50920624">8.2.1. Introduction</a></span></dt><dt><span class="section"><a href="#idp55550160">8.2.2. Lease Storage</a></span></dt><dt><span class="section"><a href="#dhcp6-interface-selection">8.2.3. Interface selection</a></span></dt><dt><span class="section"><a href="#ipv6-subnet-id">8.2.4. IPv6 Subnet Identifier</a></span></dt><dt><span class="section"><a href="#dhcp6-unicast">8.2.5. Unicast traffic support</a></span></dt><dt><span class="section"><a href="#dhcp6-address-config">8.2.6. Subnet and Address Pool</a></span></dt><dt><span class="section"><a href="#idp55239488">8.2.7. Subnet and Prefix Delegation Pools</a></span></dt><dt><span class="section"><a href="#dhcp6-std-options">8.2.8. Standard DHCPv6 options</a></span></dt><dt><span class="section"><a href="#dhcp6-custom-options">8.2.9. Custom DHCPv6 options</a></span></dt><dt><span class="section"><a href="#dhcp6-vendor-opts">8.2.10. DHCPv6 vendor specific options</a></span></dt><dt><span class="section"><a href="#dhcp6-option-spaces">8.2.11. Nested DHCPv6 options (custom option spaces)</a></span></dt><dt><span class="section"><a href="#dhcp6-option-data-defaults">8.2.12. Unspecified parameters for DHCPv6 option configuration</a></span></dt><dt><span class="section"><a href="#dhcp6-config-subnets">8.2.13. IPv6 Subnet Selection</a></span></dt><dt><span class="section"><a href="#dhcp6-rapid-commit">8.2.14. Rapid Commit</a></span></dt><dt><span class="section"><a href="#dhcp6-relays">8.2.15. DHCPv6 Relays</a></span></dt><dt><span class="section"><a href="#dhcp6-rsoo">8.2.16. Relay-Supplied Options</a></span></dt><dt><span class="section"><a href="#dhcp6-client-classifier">8.2.17. Client Classification in DHCPv6</a></span></dt><dt><span class="section"><a href="#dhcp6-ddns-config">8.2.18. Configuring DHCPv6 for DDNS</a></span></dt></dl></dd><dt><span class="section"><a href="#host-reservation-v6">8.3. Host reservation in DHCPv6</a></span></dt><dd><dl><dt><span class="section"><a href="#reservation6-types">8.3.1. Address/prefix reservation types</a></span></dt><dt><span class="section"><a href="#reservation6-conflict">8.3.2. Conflicts in DHCPv6 reservations</a></span></dt><dt><span class="section"><a href="#reservation6-hostname">8.3.3. Reserving a hostname</a></span></dt><dt><span class="section"><a href="#reservation6-options">8.3.4. Reserving specific options</a></span></dt><dt><span class="section"><a href="#reservation6-mode">8.3.5. Fine Tuning IPv6 Host Reservation</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp6-serverid">8.4. Server Identifier in DHCPv6</a></span></dt><dt><span class="section"><a href="#stateless-dhcp6">8.5. Stateless DHCPv6 (Information-Request Message)</a></span></dt><dt><span class="section"><a href="#dhcp6-rfc7550">8.6. Support for RFC 7550</a></span></dt><dt><span class="section"><a href="#dhcp6-relay-override">8.7. Using specific relay agent for a subnet</a></span></dt><dt><span class="section"><a href="#dhcp6-client-class-relay">8.8. Segregating IPv6 clients in a cable network</a></span></dt><dt><span class="section"><a href="#mac-in-dhcpv6">8.9. MAC/Hardware addresses in DHCPv6</a></span></dt><dt><span class="section"><a href="#dhcp6-decline">8.10. Duplicate Addresses (DECLINE support)</a></span></dt><dt><span class="section"><a href="#dhcp6-stats">8.11. Statistics in DHCPv6 server</a></span></dt><dt><span class="section"><a href="#dhcp6-ctrl-channel">8.12. Management API for the DHCPv6 server</a></span></dt><dt><span class="section"><a href="#dhcp6-std">8.13. Supported DHCPv6 Standards</a></span></dt><dt><span class="section"><a href="#dhcp6-limit">8.14. DHCPv6 Server Limitations</a></span></dt></dl></dd><dt><span class="chapter"><a href="#lease-expiration">9. Lease Expiration in DHCPv4 and DHCPv6</a></span></dt><dd><dl><dt><span class="section"><a href="#lease-reclamation">9.1. Lease Reclamation</a></span></dt><dt><span class="section"><a href="#lease-reclaim-config">9.2. Configuring Leases Reclamation</a></span></dt><dt><span class="section"><a href="#lease-affinity">9.3. Configuring Lease Affinity</a></span></dt><dt><span class="section"><a href="#lease-reclamation-defaults">9.4. Default Configuration Values for Leases Reclamation</a></span></dt><dt><span class="section"><a href="#leases-reclamation-using-command">9.5. Reclaiming Expired Leases with Command</a></span></dt></dl></dd><dt><span class="chapter"><a href="#dhcp-ddns-server">10. The DHCP-DDNS Server</a></span></dt><dd><dl><dt><span class="section"><a href="#dhcp-ddns-server-start-stop">10.1. Starting and Stopping the DHCP-DDNS Server</a></span></dt><dt><span class="section"><a href="#d2-configuration">10.2. Configuring the DHCP-DDNS Server</a></span></dt><dd><dl><dt><span class="section"><a href="#d2-server-parameter-config">10.2.1. Global Server Parameters</a></span></dt><dt><span class="section"><a href="#d2-tsig-key-list-config">10.2.2. TSIG Key List</a></span></dt><dt><span class="section"><a href="#d2-forward-ddns-config">10.2.3. Forward DDNS</a></span></dt><dt><span class="section"><a href="#d2-reverse-ddns-config">10.2.4. Reverse DDNS</a></span></dt><dt><span class="section"><a href="#d2-exmaple-config">10.2.5. Example DHCP-DDNS Server Configuration</a></span></dt></dl></dd><dt><span class="section"><a href="#idp55495520">10.3. DHCP-DDNS Server Limitations</a></span></dt></dl></dd><dt><span class="chapter"><a href="#kea-lfc">11. The LFC process</a></span></dt><dd><dl><dt><span class="section"><a href="#kea-lfc-overview">11.1. Overview</a></span></dt><dt><span class="section"><a href="#kea-lfc-usage">11.2. Command Line Options</a></span></dt></dl></dd><dt><span class="chapter"><a href="#classify">12. Client Classification</a></span></dt><dd><dl><dt><span class="section"><a href="#idp49591728">12.1. Client Classification Overview</a></span></dt><dt><span class="section"><a href="#classification-using-vendor">12.2. Using Vendor Class Information In Classification</a></span></dt><dt><span class="section"><a href="#classification-using-expressions">12.3. Using Expressions In Classification</a></span></dt><dd><dl><dt><span class="section"><a href="#idp55587760">12.3.1. Substring</a></span></dt></dl></dd><dt><span class="section"><a href="#classification-configuring">12.4. Configuring Classes</a></span></dt><dt><span class="section"><a href="#classification-subnets">12.5. Configuring Subnets With Class Information</a></span></dt><dt><span class="section"><a href="#idp55504128">12.6. Using Classes</a></span></dt><dt><span class="section"><a href="#idp55506384">12.7. Classes and Hooks</a></span></dt></dl></dd><dt><span class="chapter"><a href="#hooks-libraries">13. Hooks Libraries</a></span></dt><dd><dl><dt><span class="section"><a href="#hooks-libraries-introduction">13.1. Introduction</a></span></dt><dt><span class="section"><a href="#idp52289920">13.2. Configuring Hooks Libraries</a></span></dt></dl></dd><dt><span class="chapter"><a href="#stats">14. Statistics</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54285232">14.1. Statistics Overview</a></span></dt><dt><span class="section"><a href="#stats-lifecycle">14.2. Statistics Lifecycle</a></span></dt><dt><span class="section"><a href="#command-stats">14.3. Commands for Manipulating Statistics</a></span></dt><dd><dl><dt><span class="section"><a href="#command-statistic-get">14.3.1. statistic-get command</a></span></dt><dt><span class="section"><a href="#command-statistic-reset">14.3.2. statistic-reset command</a></span></dt><dt><span class="section"><a href="#command-statistic-remove">14.3.3. statistic-remove command</a></span></dt><dt><span class="section"><a href="#command-statistic-get-all">14.3.4. statistic-get-all command</a></span></dt><dt><span class="section"><a href="#command-statistic-reset-all">14.3.5. statistic-reset-all command</a></span></dt><dt><span class="section"><a href="#command-statistic-remove-all">14.3.6. statistic-remove-all command</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#ctrl-channel">15. Management API</a></span></dt><dd><dl><dt><span class="section"><a href="#ctrl-channel-syntax">15.1. Data syntax</a></span></dt><dt><span class="section"><a href="#ctrl-channel-client">15.2. Using control channel</a></span></dt><dt><span class="section"><a href="#commands-common">15.3. Commands supported by both DHCPv4 and DHCPv6 servers</a></span></dt><dd><dl><dt><span class="section"><a href="#command-leases-reclaim">15.3.1. leases-reclaim command</a></span></dt><dt><span class="section"><a href="#command-list-commands">15.3.2. list-commands command</a></span></dt><dt><span class="section"><a href="#command-shutdown">15.3.3. shutdown command</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#libdhcp">16. libdhcp++ library</a></span></dt><dd><dl><dt><span class="section"><a href="#iface-detect">16.1. Interface detection and Socket handling</a></span></dt></dl></dd><dt><span class="chapter"><a href="#logging">17. Logging</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54587936">17.1. Logging Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp50497936">17.1.1. Loggers</a></span></dt><dt><span class="section"><a href="#idp54763552">17.1.2. Output Options</a></span></dt><dt><span class="section"><a href="#idp54783056">17.1.3. Example Logger Configurations</a></span></dt></dl></dd><dt><span class="section"><a href="#logging-message-format">17.2. Logging Message Format</a></span></dt><dt><span class="section"><a href="#idp52337216">17.3. Logging During Kea Startup</a></span></dt></dl></dd><dt><span class="chapter"><a href="#faq">18. Frequently Asked Questions</a></span></dt><dd><dl><dt><span class="section"><a href="#faq-generic">18.1. Generic Frequently Asked Questions</a></span></dt><dd><dl><dt><span class="section"><a href="#q1-generic">18.1.1. Where did the Kea name came from?</a></span></dt><dt><span class="section"><a href="#q2-generic">18.1.2. Feature X is not supported yet. When/if will it be available?</a></span></dt></dl></dd><dt><span class="section"><a href="#faq-dhcp4">18.2. Frequently Asked Questions about DHCPv4</a></span></dt><dd><dl><dt><span class="section"><a href="#idp51413776">18.2.1. I set up a firewall, but the Kea server still receives the traffic. Why?</a></span></dt></dl></dd><dt><span class="section"><a href="#faq-dhcp6">18.3. Frequently Asked Questions about DHCPv6</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54575072">18.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I checked with tcpdump (or other traffic
capture software) that the incoming traffic is reaching the box. What's wrong?</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#acknowledgments">19. Acknowledgments</a></span></dt></dl></div><div class="list-of-tables"><p><b>List of Tables</b></p><dl><dt>7.1. <a href="#dhcp4-std-options-list">List of standard DHCPv4 options</a></dt><dt>7.2. <a href="#dhcp4-std-options-list-part2">List of standard DHCPv4 options (continued)</a></dt><dt>7.3. <a href="#dhcp-types">List of standard DHCP option types</a></dt><dt>7.4. <a href="#fqdn-flag-table">Default FQDN Flag Behavior</a></dt><dt>7.5. <a href="#dhcp4-statistics">DHCPv4 Statistics</a></dt><dt>8.1. <a href="#dhcp6-std-options-list">List of standard DHCPv6 options</a></dt><dt>8.2. <a href="#dhcp6-exp-options-list">List of experimental DHCPv6 options</a></dt><dt>8.3. <a href="#dhcp6-fqdn-flag-table">Default FQDN Flag Behavior</a></dt><dt>8.4. <a href="#dhcp6-statistics">DHCPv6 Statistics</a></dt><dt>10.1. <a href="#idp55451472">Our example network</a></dt><dt>10.2. <a href="#idp55465872">Forward DDNS Domains Needed</a></dt><dt>10.3. <a href="#idp55480416">Reverse DDNS Domains Needed</a></dt><dt>12.1. <a href="#classification-values-list">List of Classification Values</a></dt><dt>12.2. <a href="#classification-expressions-list">List of Classification Expressions</a></dt></dl></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="intro"></a>Chapter 1. Introduction</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idp50568016">1.1. Supported Platforms</a></span></dt><dt><span class="section"><a href="#required-software">1.2. Required Software at Run-time</a></span></dt><dt><span class="section"><a href="#kea_software">1.3. Kea Software</a></span></dt></dl></div><p>
Kea is the next generation of DHCP software developed by ISC.
It supports both DHCPv4 and DHCPv6 protocols along with their
extensions, e.g. prefix delegation and dynamic updates to DNS.
</p><p>
Kea was initially developed as a part of the BIND 10 framework.
In early 2014, ISC made the decision to discontinue active
development of BIND 10 and continue development of Kea as
standalone DHCP software.
</p><p>
This guide covers Kea version 1.0.0.
</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp50568016"></a>1.1. Supported Platforms</h2></div></div></div><p>
Kea is officially supported on Red Hat Enterprise Linux,
CentOS, Fedora and FreeBSD systems. It is also likely to work on many
other platforms: builds have been tested on (in no particular order)
Debian GNU/Linux 6 and unstable, Ubuntu 9.10, NetBSD 5,
Solaris 10 and 11, FreeBSD 7 and 8, CentOS Linux 5.3,
MacOS 10.6 and 10.7, and OpenBSD 5.1. Non supported systems
(especially non-Linux) are likely to have issues with directly
connected DHCPv4 clients.
</p><p>There are currently no plans to port Kea to Windows platforms.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="required-software"></a>1.2. Required Software at Run-time</h2></div></div></div><p>
Running Kea uses various extra software which may
not be provided in the default installation of some operating systems,
nor in the standard package collections. You may
need to install this required software separately.
(For the build requirements, also see
<a class="xref" href="#build-requirements" title="3.3. Building Requirements">Section 3.3, “Building Requirements”</a>.)
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Kea supports two crypto libraries: Botan and OpenSSL. Only one of them
is required to be installed during compilation. Kea uses the Botan
crypto library for C++ (<a class="ulink" href="http://botan.randombit.net/" target="_top">http://botan.randombit.net/</a>),
version 1.8 or later. As an alternative to Botan, Kea can use the
OpenSSL crypto library (<a class="ulink" href="http://www.openssl.org/" target="_top">http://www.openssl.org/</a>).
It requires a version with SHA-2 support.
</li><li class="listitem">
Kea uses the log4cplus C++ logging library
(<a class="ulink" href="http://log4cplus.sourceforge.net/" target="_top">http://log4cplus.sourceforge.net/</a>).
It requires at least log4cplus version 1.0.3.
</li><li class="listitem">
In order to store lease information in a MySQL database, Kea requires MySQL
headers and libraries. This is an optional dependency in that Kea can be
built without MySQL support.
</li><li class="listitem">
In order to store lease information in a PostgreSQL database, Kea requires PostgreSQL
headers and libraries. This is an optional dependency in that Kea can be
built without PostgreSQL support.
</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kea_software"></a>1.3. Kea Software</h2></div></div></div><p>
Kea is modular. Part of this modularity is
accomplished using multiple cooperating processes which, together,
provide the server functionality.
The following software is included with Kea:
</p><p>
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>keactrl</strong></span> —
Tool to start, stop, reconfigure, and report status
for the Kea servers.
</li><li class="listitem">
<span class="command"><strong>kea-dhcp4</strong></span> —
DHCPv4 server process.
This process responds to DHCPv4 queries from clients.
</li><li class="listitem">
<span class="command"><strong>kea-dhcp6</strong></span> —
DHCPv6 server process.
This process responds to DHCPv6 queries from clients.
</li><li class="listitem">
<span class="command"><strong>kea-dhcp-ddns</strong></span> —
DHCP-DDNS process.
This process acts as an intermediary between the DHCP servers
and DNS server. It receives name update requests from the DHCP
servers and sends DNS Update messages to the DNS servers.
</li><li class="listitem">
<span class="command"><strong>kea-admin</strong></span> —
A tool useful for database backend maintenance (creating new
database, checking versions, upgrading etc.)
</li><li class="listitem">
<span class="command"><strong>kea-lfc</strong></span> —
This process removes redundant information from the files used
to provide persistent storage for the memfile data base backend.
The service is written to run as a stand alone process. While it
can be started externally it should be started by the Kea DHCP
servers.
</li><li class="listitem">
<span class="command"><strong>perfdhcp</strong></span> —
DHCP benchmarking tool which simulates multiple clients to
test both DHCPv4 and DHCPv6 servers performance.
</li></ul></div><p>
</p></div><p>
The tools and modules are covered in full detail in this guide.
In addition, manual pages are also provided in the default installation.
</p><p>
Kea also provides C++ libraries and programmer interfaces for
DHCP. These include detailed developer documentation and
code examples.
</p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="quickstart"></a>Chapter 2. Quick start</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#quick-start">2.1. Quick start guide for DHCPv4 and DHCPv6 services</a></span></dt><dt><span class="section"><a href="#quick-start-direct-run">2.2. Running Kea servers directly</a></span></dt></dl></div><p>
This quickly covers the standard steps for installing and deploying Kea.
For further details, full customizations, and troubleshooting, see the
respective chapters in the Kea guide.
</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="quick-start"></a>2.1. Quick start guide for DHCPv4 and DHCPv6 services</h2></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
Install required run-time and build dependencies. See <a class="xref" href="#build-requirements" title="3.3. Building Requirements">Section 3.3, “Building Requirements”</a> for details.
</li><li class="listitem"><p>
Download Kea source tarball from <a class="ulink" href="https://www.isc.org/downloads/" target="_top">ISC.org downloads page</a> or <a class="ulink" href="http://ftp.isc.org/isc/kea/" target="_top">ISC ftp server</a>.
</p></li><li class="listitem"><p>
Extract the tarball. For example:
</p><pre class="screen">$ <strong class="userinput"><code>tar xvzf kea-1.0.0.tar.gz</code></strong></pre><p>
</p></li><li class="listitem"><p>Go into the source directory and run the configure script:
</p><pre class="screen">$ <strong class="userinput"><code>cd kea-1.0.0</code></strong>
$ <strong class="userinput"><code>./configure [your extra parameters]</code></strong></pre><p>
</p></li><li class="listitem"><p>Build it:
</p><pre class="screen">$ <strong class="userinput"><code>make</code></strong></pre><p>
</p></li><li class="listitem"><p>Install it (by default the installation prefix is <code class="filename">/usr/local/</code>,
so you likely need root privileges for that step):
</p><pre class="screen"># <strong class="userinput"><code>make install</code></strong></pre><p>
</p></li><li class="listitem"><p>Edit the configuration file which by default is installed in
<code class="filename">[kea-install-dir]/etc/kea/kea.conf</code> and contains
configuration for all Kea services. Configuration choices for DHCPv4
and DHCPv6 services are described in <a class="xref" href="#dhcp4-configuration" title="7.2. DHCPv4 Server Configuration">Section 7.2, “DHCPv4 Server Configuration”</a> and <a class="xref" href="#dhcp6-configuration" title="8.2. DHCPv6 Server Configuration">Section 8.2, “DHCPv6 Server Configuration”</a>, respectively.</p></li><li class="listitem"><p>In order to start the DHCPv4 server in background, run the
following command (as root):
</p><pre class="screen"># <strong class="userinput"><code>keactrl start -s dhcp4</code></strong></pre><p>
Or run the following command to start DHCPv6 server instead:
</p><pre class="screen"># <strong class="userinput"><code>keactrl start -s dhcp6</code></strong></pre><p>
Note that it is also possible to start both servers simultaneously:
</p><pre class="screen">$ <strong class="userinput"><code>keactrl start</code></strong></pre><p>
</p></li><li class="listitem"><p>Verify that Kea server(s) are running:
</p><pre class="screen"># <strong class="userinput"><code>keactrl status</code></strong></pre><p>
If the server status is "inactive" may indicate a configuration
error. Please check a log file (by default located in
<code class="filename">[kea-install-dir]/var/kea/kea.log</code>) for the
details of the error.
</p></li><li class="listitem"><p>
If the server has been started successfully, test that it is
responding to DHCP queries and that the client
receives a configuration from the server; for example, use
the <a class="ulink" href="http://www.isc.org/downloads/DHCP/" target="_top">ISC DHCP client</a>.
</p></li><li class="listitem"><p>
Stop running server(s):
</p><pre class="screen"># <strong class="userinput"><code>keactrl stop</code></strong></pre><p>
</p></li></ol></div><p>
For more system specific installation procedures, you may want to visit
<a class="ulink" href="http://kea.isc.org/wiki/SystemSpecificNotes" target="_top">System specific notes</a>,
available on <a class="ulink" href="http://kea.isc.org/" target="_top">Kea homepage</a>.
</p><p>The details of <span class="command"><strong>keactrl</strong></span> script usage can be found
in <a class="xref" href="#keactrl" title="Chapter 6. Managing Kea with keactrl">Chapter 6, <i>Managing Kea with keactrl</i></a>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="quick-start-direct-run"></a>2.2. Running Kea servers directly</h2></div></div></div><p>Kea servers can be started directly (without a need to use
<span class="command"><strong>keactrl</strong></span>). To start DHCPv4 server run the following
command:
</p><pre class="screen"># <strong class="userinput"><code>kea-dhcp4 -c /path/to/your/kea4/config/file.json</code></strong></pre><p>
And, to start the DHCPv6 server run the following command:
</p><pre class="screen"># <strong class="userinput"><code>kea-dhcp6 -c /path/to/your/kea6/config/file.json</code></strong></pre><p>
</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="installation"></a>Chapter 3. Installation</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#packages">3.1. Packages</a></span></dt><dt><span class="section"><a href="#install-hierarchy">3.2. Install Hierarchy</a></span></dt><dt><span class="section"><a href="#build-requirements">3.3. Building Requirements</a></span></dt><dt><span class="section"><a href="#install">3.4. Installation from Source</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54877744">3.4.1. Download Tar File</a></span></dt><dt><span class="section"><a href="#idp54879728">3.4.2. Retrieve from Git</a></span></dt><dt><span class="section"><a href="#configure">3.4.3. Configure before the build</a></span></dt><dt><span class="section"><a href="#idp51819024">3.4.4. Build</a></span></dt><dt><span class="section"><a href="#idp51821792">3.4.5. Install</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp-config-backend">3.5. Selecting the Configuration Backend</a></span></dt><dt><span class="section"><a href="#dhcp-install-configure">3.6. DHCP Database Installation and Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp51839952">3.6.1. Building with MySQL Support</a></span></dt><dt><span class="section"><a href="#idp51846720">3.6.2. Building with PostgreSQL support</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="packages"></a>3.1. Packages</h2></div></div></div><p>
Some operating systems or software package vendors may provide
ready-to-use, pre-built software packages for Kea. Installing a
pre-built package means you do not need to install build-only
prerequisites and do not need to <span class="emphasis"><em>make</em></span> the software.
</p><p>
FreeBSD ports, NetBSD pkgsrc, and Debian <span class="emphasis"><em>testing</em></span>
package collections provide all the prerequisite packages.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="install-hierarchy"></a>3.2. Install Hierarchy</h2></div></div></div><p>
The following is the directory layout of the complete Kea installation
(all directories paths are relative to the installation directory):
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<code class="filename">etc/kea/</code> —
configuration files.
</li><li class="listitem">
<code class="filename">include/</code> —
C++ development header files.
</li><li class="listitem">
<code class="filename">lib/</code> —
libraries.
</li><li class="listitem">
<code class="filename">sbin/</code> —
server software and commands used by the system administrator.
</li><li class="listitem">
<code class="filename">share/kea/</code> —
configuration specifications and examples.
</li><li class="listitem">
<code class="filename">share/doc/kea/</code> —
this guide, other supplementary documentation, and examples.
</li><li class="listitem">
<code class="filename">share/man/</code> —
manual pages (online documentation).
</li><li class="listitem">
<code class="filename">var/kea/</code> —
server identification, lease databases, and log files.
</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="build-requirements"></a>3.3. Building Requirements</h2></div></div></div><p>
In addition to the run-time requirements (listed in <a class="xref" href="#required-software" title="1.2. Required Software at Run-time">Section 1.2, “Required Software at Run-time”</a>), building Kea from source code requires
various development include headers and program development tools.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Some operating systems have split their distribution packages into
a run-time and a development package. You will need to install
the development package versions, which include header files and
libraries, to build Kea from the source code.
</p></div><p>
Building from source code requires the following software installed
on the system:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Boost build-time headers
(<a class="ulink" href="http://www.boost.org/" target="_top">http://www.boost.org/</a>).
At least Boost version 1.35 is required.
When header-only Boost error code is not available or wanted, the
Boost system library is required too.
</p></li><li class="listitem"><p>
Botan (at least version 1.8) or OpenSSL.</p></li><li class="listitem"><p>
log4cplus (at least version 1.0.3)
development include headers.
</p></li><li class="listitem"><p>
A C++ compiler and
standard development headers.
Kea builds have been tested with GCC g++ 3.4.3, 4.1.2,
4.1.3, 4.2.1, 4.3.2, and 4.4.1; Clang++ 2.8; and Sun C++ 5.10.
</p></li><li class="listitem"><p>
The development tools "make".
</p></li></ul></div><p>
Visit the user-contributed wiki at <a class="ulink" href="http://kea.isc.org/wiki/SystemSpecificNotes" target="_top">http://kea.isc.org/wiki/SystemSpecificNotes</a>
for system-specific installation tips.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="install"></a>3.4. Installation from Source</h2></div></div></div><p>
Kea is open source software written in C++.
It is freely available in source code form from ISC as a
downloadable tar file or via Kea Git code revision control
service. (It may also be available in pre-compiled ready-to-use
packages from operating system vendors.)
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54877744"></a>3.4.1. Download Tar File</h3></div></div></div><p>
The Kea release tarballs may be downloaded from:
<a class="ulink" href="http://ftp.isc.org/isc/kea/" target="_top">http://ftp.isc.org/isc/kea/</a> (using FTP or HTTP).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54879728"></a>3.4.2. Retrieve from Git</h3></div></div></div><p>
Downloading this "bleeding edge" code is recommended only for
developers or advanced users. Using development code in a production
environment is not recommended.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
When building from source code retrieved via Git, additional
software will be required: automake (v1.11 or later),
libtoolize, and autoconf (2.59 or later).
These may need to be installed.
</p></div><p>
The latest development code (together with temporary experiments
and un-reviewed code) is available via the Kea code revision
control system. This is powered by Git and all the Kea
development is public.
The leading development is done in the <span class="quote">“<span class="quote">master</span>”</span>
branch.
</p><p>
The code can be checked out from
<code class="filename">git://git.kea.isc.org/kea</code>:
</p><pre class="screen">$ <strong class="userinput"><code>git clone git://git.kea.isc.org/kea</code></strong></pre><p>
</p><p>
The code checked out from the git repository doesn't include the
generated configure script, Makefile.in files, nor their
related build files.
They can be created by running <span class="command"><strong>autoreconf</strong></span>
with the <code class="option">--install</code> switch.
This will run <span class="command"><strong>autoconf</strong></span>,
<span class="command"><strong>aclocal</strong></span>,
<span class="command"><strong>libtoolize</strong></span>,
<span class="command"><strong>autoheader</strong></span>,
<span class="command"><strong>automake</strong></span>,
and related commands.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="configure"></a>3.4.3. Configure before the build</h3></div></div></div><p>
Kea uses the GNU Build System to discover build environment
details.
To generate the makefiles using the defaults, simply run:
</p><pre class="screen">$ <strong class="userinput"><code>./configure</code></strong></pre><p>
</p><p>
Run <span class="command"><strong>./configure</strong></span> with the <code class="option">--help</code>
switch to view the different options. Some commonly-used options are:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">--prefix</span></dt><dd>Define the installation location (the
default is <code class="filename">/usr/local</code>).
</dd><dt><span class="term">--with-boost-include</span></dt><dd>Define the path to find the Boost headers.
</dd><dt><span class="term">--with-boost-libs</span></dt><dd>Specify Boost libraries to link with (this option
exists only to provide a way to enforce such a list:
usually this should not be used).
</dd><dt><span class="term">--with-boost-lib-dir</span></dt><dd>Specify the path to Boost libraries to link with
(usually there should be no reason to specify this option).
</dd><dt><span class="term">--with-botan-config</span></dt><dd>Specify the path to the botan-config
script to build with Botan for the crypto code.
</dd><dt><span class="term">--with-gtest</span></dt><dd>Enable the building of the C++ Unit Tests using the
Google Test framework. Optionally this can define the
path to the gtest header files and library. (If the framework
is not already installed on your system, it can be downloaded
from <a class="ulink" href="https://code.google.com/p/googletest" target="_top">https://code.google.com/p/googletest</a>.)
</dd><dt><span class="term">--with-log4cplus</span></dt><dd>Define the path to find the Log4cplus headers
and libraries.
</dd><dt><span class="term">--with-openssl</span></dt><dd>Replace Botan by OpenSSL for the crypto library.
The default is to try to find a working Botan then
OpenSSL only if Botan is not found.
</dd><dt><span class="term">--without-werror</span></dt><dd>Disable the default use of the
<code class="option">-Werror</code> compiler flag so that
compiler warnings do not result in build failures.
</dd></dl></div><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
For additional instructions concerning the building and installation of
Kea for various databases, see <a class="xref" href="#dhcp-install-configure" title="3.6. DHCP Database Installation and Configuration">Section 3.6, “DHCP Database Installation and Configuration”</a>.
For additional instructions concerning the configuration backends, see
<a class="xref" href="#dhcp-config-backend" title="3.5. Selecting the Configuration Backend">Section 3.5, “Selecting the Configuration Backend”</a>.
</p></div><p>
</p><p>
For example, the following command configures Kea to find the
Boost headers in /usr/pkg/include, specifies that PostgreSQL
support should be enabled, and sets the installation location
to /opt/kea:
</p><pre class="screen">$ <strong class="userinput"><code>./configure \
--with-boost-include=/usr/pkg/include \
--with-dhcp-pgsql=/usr/local/bin/pg_config \
--prefix=/opt/kea</code></strong></pre><p>
</p><p>
If you have some problems with building Kea using the header-only
Boost error code or you'd like to use the Boost system library
(e.g., located in /usr/pkg/lib):
</p><pre class="screen">$ <strong class="userinput"><code>./configure \
--with-boost-libs=-lboost_system \
--with-boost-lib-dir=/usr/pkg/lib</code></strong></pre><p>
</p><p>
If the configure fails, it may be due to missing or old
dependencies.
</p><p>
<strong class="userinput"><code>./configure</code></strong> when it succeeds displays a report
with the building parameters. This report is saved into
<code class="filename">config.report</code> and embedded into executable
binaries, e.g., <strong class="userinput"><code>kea-dhcp4</code></strong>.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51819024"></a>3.4.4. Build</h3></div></div></div><p>
After the configure step is complete, build the executables
from the C++ code and prepare the Python scripts by running the command:
</p><pre class="screen">$ <strong class="userinput"><code>make</code></strong></pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51821792"></a>3.4.5. Install</h3></div></div></div><p>
To install the Kea executables, support files,
and documentation, issue the command:
</p><pre class="screen">$ <strong class="userinput"><code>make install</code></strong></pre><p>
</p><p>
Do not use any form of parallel or job server options
(such as GNU make's <span class="command"><strong>-j</strong></span> option) when
performing this step: doing so may cause errors.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The install step may require superuser privileges.</p></div><p>
If required, run <span class="command"><strong>ldconfig</strong></span> as root with
<code class="filename">/usr/local/lib</code> (or with ${prefix}/lib if
configured with --prefix) in
<code class="filename">/etc/ld.so.conf</code> (or the relevant linker
cache configuration file for your OS):
</p><pre class="screen">$ <strong class="userinput"><code>ldconfig</code></strong></pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
If you do not run <span class="command"><strong>ldconfig</strong></span> where it is
required, you may see errors like the following:
</p><pre class="screen">
program: error while loading shared libraries: libkea-something.so.1:
cannot open shared object file: No such file or directory
</pre><p>
</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp-config-backend"></a>3.5. Selecting the Configuration Backend</h2></div></div></div><p>Kea 0.9 has introduced configuration backends that are
switchable during the compilation phase. Only one backend, JSON,
is currently supported.
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">JSON</span></dt><dd>JSON is the new default configuration backend
that causes Kea to read JSON configuration files from
disk. It does not require any framework and thus is
considered more lightweight. It will allow dynamic
on-line reconfiguration, but will lack remote capabilities
(i.e. no RESTful API).</dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp-install-configure"></a>3.6. DHCP Database Installation and Configuration</h2></div></div></div><p>
Kea stores its leases in a lease database. The software has been written in
a way that makes it possible to choose which database product should be used to
store the lease information. At present, Kea supports three database backends: MySQL,
PostgreSQL and Memfile. To limit external dependencies, both MySQL and PostgreSQL
support are disabled by default and only Memfile
is available. Support for the optional external database backend must be explicitly included when
Kea is built. This section covers the building of Kea with MySQL and/or PostgreSQL
and the creation of the lease database.
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51839952"></a>3.6.1. Building with MySQL Support</h3></div></div></div><p>
Install MySQL according to the instructions for your system. The client development
libraries must be installed.
</p><p>
Build and install Kea as described in <a class="xref" href="#installation" title="Chapter 3. Installation">Chapter 3, <i>Installation</i></a>, with
the following modification. To enable the MySQL database code, at the
"configure" step (see <a class="xref" href="#configure" title="3.4.3. Configure before the build">Section 3.4.3, “Configure before the build”</a>), do:
</p><pre class="screen"><strong class="userinput"><code>./configure [other-options] --with-dhcp-mysql</code></strong></pre><p>
Or specify the location of the MySQL configuration program
"mysql_config" if MySQL was not installed in the default location:
</p><pre class="screen"><strong class="userinput"><code>./configure [other-options] --with-dhcp-mysql=<em class="replaceable"><code>path-to-mysql_config</code></em></code></strong></pre><p>
</p><p>
See <a class="xref" href="#mysql-database-create" title="4.3.2.1. First Time Creation of Kea Database">Section 4.3.2.1, “First Time Creation of Kea Database”</a> for details regarding
MySQL database configuration.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51846720"></a>3.6.2. Building with PostgreSQL support</h3></div></div></div><p>
Install PostgreSQL according to the instructions for your system. The client development
libraries must be installed. Client development libraries are often packaged as "libpq".
</p><p>
Build and install Kea as described in <a class="xref" href="#installation" title="Chapter 3. Installation">Chapter 3, <i>Installation</i></a>, with
the following modification. To enable the PostgreSQL database code, at the
"configure" step (see <a class="xref" href="#configure" title="3.4.3. Configure before the build">Section 3.4.3, “Configure before the build”</a>), do:
</p><pre class="screen"><strong class="userinput"><code>./configure [other-options] --with-dhcp-pgsql</code></strong></pre><p>
Or specify the location of the PostgreSQL configuration
program "pg_config" if PostgreSQL was not installed in
the default location:
</p><pre class="screen"><strong class="userinput"><code>./configure [other-options] --with-dhcp-pgsql=<em class="replaceable"><code>path-to-pg_config</code></em></code></strong></pre><p>
</p><p>
See <a class="xref" href="#pgsql-database-create" title="4.3.3.1. Manually Create the PostgreSQL Database and the Kea User">Section 4.3.3.1, “Manually Create the PostgreSQL Database and the Kea User”</a> for details regarding
PostgreSQL database configuration.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="admin"></a>Chapter 4. Kea Database Administration</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#kea-database-version">4.1. Databases and Database Version Numbers</a></span></dt><dt><span class="section"><a href="#kea-admin">4.2. The kea-admin Tool</a></span></dt><dt><span class="section"><a href="#idp54116336">4.3. Supported Databases</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54117072">4.3.1. memfile</a></span></dt><dt><span class="section"><a href="#idp53820304">4.3.2. MySQL</a></span></dt><dt><span class="section"><a href="#idp51946336">4.3.3. PostgreSQL</a></span></dt><dt><span class="section"><a href="#idp51986896">4.3.4. Limitations related to the use of the SQL databases</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kea-database-version"></a>4.1. Databases and Database Version Numbers</h2></div></div></div><p>
Kea stores leases in one of several supported databases.
As future versions of Kea are released, the structure of those
databases will change. For example, Kea currently only stores
lease information: in the future, additional data - such as host
reservation details - will also be stored.
</p><p>
A given version of Kea expects a particular structure in
the database. It ensures this by checking the version of the
database it is using. Separate version numbers are maintained for
backend databases, independent of the version of Kea itself. It
is possible that the backend database version will stay the same
through several Kea revisions. Likewise, it is possible that the
version of backend database may go up several revisions during a
Kea upgrade. Versions for each database are independent, so an
increment in the MySQL database version does not imply an increment
in that of PostgreSQL.
</p><p>
Backend versions are specified in
a <em class="replaceable"><code>major.minor</code></em> format. The minor
number is increased when there are backward compatible changes
introduced. For example, the addition of a new index. It is
desirable, but not mandatory to apply such a change; you
can run on older database version if you want to. (Although, in
the example given, running without the new index may be at the
expense of a performance penalty.) On the other hand, the major
number is increased when an incompatible change is introduced,
for example an extra column is added to a table. If you try to
run Kea software on a database that is too old (as signified by
mismatched backend major version number), Kea will refuse to run:
administrative action will be required to upgrade the database.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kea-admin"></a>4.2. The kea-admin Tool</h2></div></div></div><p>
To manage the databases, Kea provides the
<span class="command"><strong>kea-admin</strong></span> tool. It is able to initialize
a new database, check its version number, perform a
database upgrade, and dump lease data to a text file.
</p><p>
<span class="command"><strong>kea-admin</strong></span> takes two mandatory
parameters: <span class="command"><strong>command</strong></span> and
<span class="command"><strong>backend</strong></span>. Additional, non-mandatory options
may be specified. Currently supported commands are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>lease-init</strong></span> —
Initializes a new lease database. Useful during first
Kea installation. The database is initialized to the
latest version supported by the version of the software.
</li><li class="listitem">
<span class="command"><strong>lease-version</strong></span> —
Reports the lease database version number. This is
not necessarily equal to the Kea version number as
each backend has its own versioning scheme.
</li><li class="listitem">
<span class="command"><strong>lease-upgrade</strong></span> —
Conducts a lease database upgrade. This is useful when
upgrading Kea.
</li><li class="listitem">
<span class="command"><strong>lease-dump</strong></span> —
Dumps the contents of the lease database (for MySQL or PostgreSQL
backends) to CSV text file. The first line of the file contains
the column names. This is meant to be used as a diagnostic
tool that provides a portable, human-readable form of lease data.
</li></ul></div><p>
<span class="command"><strong>backend</strong></span> specifies the backend type. Currently
supported types are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>memfile</strong></span> — Lease information is
stored on disk in a text file.
</li><li class="listitem">
<span class="command"><strong>mysql</strong></span> —
Lease information is stored in a MySQL relational
database.
</li><li class="listitem">
<span class="command"><strong>pgsql</strong></span> —
Lease information is stored in a PostgreSQL relational
database.
</li></ul></div><p>
Additional parameters may be needed, depending on your setup
and specific operation: username, password and database name or
the directory where specific files are located. See appropriate
manual page for details (<span class="command"><strong>man 8 kea-admin</strong></span>).
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp54116336"></a>4.3. Supported Databases</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54117072"></a>4.3.1. memfile</h3></div></div></div><p>
There are no special initialization steps necessary
for the memfile backend. During the first run, both
<span class="command"><strong>kea-dhcp4</strong></span> and <span class="command"><strong>kea-dhcp6</strong></span>
will create an empty lease file if one is not
present. Necessary disk write permission is required.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="memfile-upgrade"></a>4.3.1.1. Upgrading Memfile Lease Files from an Earlier Version of Kea</h4></div></div></div><p>
There are no special steps required to upgrade memfile lease files
from an earlier version of Kea to a new version of Kea.
During startup the servers will check the schema version of the lease
files against their own. If there is a mismatch, the servers will
automatically launch the LFC process to convert the files to the
server's schema version. While this mechanism is primarily meant to
ease the process of upgrading to newer versions of Kea, it can also
be used for downgrading should the need arise. When upgrading, any
values not present in the original lease files will be assigned
appropriate default values. When downgrading, any data present in
the files but not in the server's schema will be dropped.
If you wish to convert the files manually, prior to starting the
servers you may do so by running the LFC process yourself.
See <a class="xref" href="#kea-lfc" title="Chapter 11. The LFC process">Chapter 11, <i>The LFC process</i></a> for more information.
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp53820304"></a>4.3.2. MySQL</h3></div></div></div><p>
The MySQL database must be properly set up if you want Kea to
store information in MySQL. This section can be safely ignored
if you chose to store the data in other backends.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mysql-database-create"></a>4.3.2.1. First Time Creation of Kea Database</h4></div></div></div><p>
If you are setting the MySQL database for the first time,
you need to create the database area within MySQL and set up
the MySQL user ID under which Kea will access the database.
This needs to be done manually: <span class="command"><strong>kea-admin</strong></span>
is not able to do this for you.
</p><p>
To create the database:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Log into MySQL as "root":
</p><pre class="screen">
$ <strong class="userinput"><code>mysql -u root -p</code></strong>
Enter password:
mysql>
</pre><p>
</p></li><li class="listitem"><p>
Create the MySQL database:
</p><pre class="screen">
mysql> <strong class="userinput"><code>CREATE DATABASE <em class="replaceable"><code>database-name</code></em>;</code></strong>
</pre><p>
(<em class="replaceable"><code>database-name</code></em> is the name
you have chosen for the database.)
</p></li><li class="listitem"><p>
Create the user under which Kea will access the database
(and give it a password), then grant it access to the
database tables:
</p><pre class="screen">
mysql> <strong class="userinput"><code>CREATE USER '<em class="replaceable"><code>user-name</code></em>'@'localhost' IDENTIFIED BY '<em class="replaceable"><code>password</code></em>';</code></strong>
mysql> <strong class="userinput"><code>GRANT ALL ON <em class="replaceable"><code>database-name</code></em>.* TO '<em class="replaceable"><code>user-name</code></em>'@'localhost';</code></strong>
</pre><p>
(<em class="replaceable"><code>user-name</code></em> and
<em class="replaceable"><code>password</code></em> are the user ID
and password you are using to allow Keas access to the
MySQL instance. All apostrophes in the command lines
above are required.)
</p></li><li class="listitem"><p>
At this point, you may elect to create the database
tables. (Alternatively, you can exit MySQL and create
the tables using the <span class="command"><strong>kea-admin</strong></span> tool,
as explained below.) To do this:
</p><pre class="screen">
mysql> <strong class="userinput"><code>CONNECT <em class="replaceable"><code>database-name</code></em>;</code></strong>
mysql> <strong class="userinput"><code>SOURCE <em class="replaceable"><code>path-to-kea</code></em>/share/kea/scripts/mysql/dhcpdb_create.mysql</code></strong>
</pre><p>
(<em class="replaceable"><code>path-to-kea</code></em> is the
location where you installed Kea.)
</p></li><li class="listitem"><p>
Exit MySQL:
</p><pre class="screen">
mysql> <strong class="userinput"><code>quit</code></strong>
Bye
$
</pre><p>
</p></li></ol></div><p>
</p><p>
If you elected not to create the tables in step 4, you can do
so now by running the <span class="command"><strong>kea-admin</strong></span> tool:
</p><pre class="screen">
$ <strong class="userinput"><code>kea-admin lease-init mysql -u <em class="replaceable"><code>database-user</code></em> -p <em class="replaceable"><code>database-password</code></em> -n <em class="replaceable"><code>database-name</code></em></code></strong>
</pre><p>
(Do not do this if you did create the tables in step 4.)
<span class="command"><strong>kea-admin</strong></span> implements rudimentary checks:
it will refuse to initialize a database that contains any
existing tables. If you want to start from scratch, you
must remove all data manually. (This process is a manual
operation on purpose to avoid possibly irretrievable mistakes
by <span class="command"><strong>kea-admin</strong></span>.)
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="mysql-upgrade"></a>4.3.2.2. Upgrading a MySQL Database from an Earlier Version of Kea</h4></div></div></div><p>
Sometimes a new Kea version may use newer database schema, so
there will be a need to upgrade the existing database. This can
be done using the <span class="command"><strong>kea-admin lease-upgrade</strong></span>
command.
</p><p>
To check the current version of the database, use the following command:
</p><pre class="screen">
$ <strong class="userinput"><code>kea-admin lease-version mysql -u <em class="replaceable"><code>database-user</code></em> -p <em class="replaceable"><code>database-password</code></em> -n <em class="replaceable"><code>database-name</code></em></code></strong>
</pre><p>
(See <a class="xref" href="#kea-database-version" title="4.1. Databases and Database Version Numbers">Section 4.1, “Databases and Database Version Numbers”</a> for a discussion
about versioning.) If the version does not match the minimum
required for the new version of Kea (as described in the
release notes), the database needs to be upgraded.
</p><p>
Before upgrading, please make sure that the database is
backed up. The upgrade process does not discard any data but,
depending on the nature of the changes, it may be impossible
to subsequently downgrade to an earlier version. To perform
an upgrade, issue the following command:
</p><pre class="screen">
$ <strong class="userinput"><code>kea-admin lease-upgrade mysql -u <em class="replaceable"><code>database-user</code></em> -p <em class="replaceable"><code>database-password</code></em> -n <em class="replaceable"><code>database-name</code></em></code></strong>
</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51946336"></a>4.3.3. PostgreSQL</h3></div></div></div><p>
A PostgreSQL database must be set up if you want Kea to store
lease and other information in PostgreSQL. This step can be
safely ignored if you are using other database backends.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="pgsql-database-create"></a>4.3.3.1. Manually Create the PostgreSQL Database and the Kea User</h4></div></div></div><p>
The first task is to create both the lease database and the
user under which the servers will access it. A number of steps
are required:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Log into PostgreSQL as "root":
</p><pre class="screen">
$ <strong class="userinput"><code>sudo -u postgres psql postgres</code></strong>
Enter password:
postgres=#
</pre><p>
</p></li><li class="listitem"><p>
Create the database:
</p><pre class="screen">
postgres=#<strong class="userinput"><code> CREATE DATABASE <em class="replaceable"><code>database-name</code></em>;</code></strong>
CREATE DATABASE
postgres=#
</pre><p>
(<em class="replaceable"><code>database-name</code></em> is the name
you have chosen for the database.)
</p></li><li class="listitem"><p>
Create the user under which Kea will access the database
(and give it a password), then grant it access to the
database:
</p><pre class="screen">
postgres=#<strong class="userinput"><code> CREATE USER <em class="replaceable"><code>user-name</code></em> WITH PASSWORD '<em class="replaceable"><code>password</code></em>';</code></strong>
CREATE ROLE
postgres=#
postgres=#<strong class="userinput"><code> GRANT ALL PRIVILEGES ON DATABASE <em class="replaceable"><code>database-name</code></em> TO <em class="replaceable"><code>user-name</code></em>;</code></strong>
GRANT
postgres=#
</pre><p>
</p></li><li class="listitem"><p>
Exit PostgreSQL:
</p><pre class="screen">
postgres=# <strong class="userinput"><code>\q</code></strong>
Bye
$
</pre><p>
</p></li><li class="listitem"><p>
At this point you are ready to create the database tables.
This can be done using the <span class="command"><strong>kea-admin</strong></span> tool
as explained in the next section (recommended), or manually.
To create the tables manually enter the following command.
Note that PostgreSQL will prompt you to enter the new user's
password you specified in Step 3. When the command completes
you will be returned to the shell prompt. You should see output
similar to following:
</p><pre class="screen">
$ <strong class="userinput"><code>psql -d <em class="replaceable"><code>database-name</code></em> -U <em class="replaceable"><code>user-name</code></em> -f <em class="replaceable"><code>path-to-kea</code></em>/share/kea/scripts/pgsql/dhcpdb_create.pgsql</code></strong>
Password for user <em class="replaceable"><code>user-name</code></em>:
CREATE TABLE
CREATE INDEX
CREATE INDEX
CREATE TABLE
CREATE INDEX
CREATE TABLE
START TRANSACTION
INSERT 0 1
INSERT 0 1
INSERT 0 1
COMMIT
CREATE TABLE
START TRANSACTION
INSERT 0 1
COMMIT
$
</pre><p>
(<em class="replaceable"><code>path-to-kea</code></em> is the location
where you installed Kea.)
</p><p>
If instead you encounter an error like:
</p><pre class="screen">
psql: FATAL: no pg_hba.conf entry for host "[local]", user "<em class="replaceable"><code>user-name</code></em>", database "<em class="replaceable"><code>database-name</code></em>", SSL off
</pre><p>
... you will need to alter the PostgreSQL configuration.
Kea uses password authentication when connecting to
the database and must have the appropriate entries
added to PostgreSQL's pg_hba.conf file. This file is
normally located in the primary data directory for your
PostgreSQL server. The precise path may vary but the
default location for PostgreSQL 9.3 on Centos 6.5 is:
<code class="filename">/var/lib/pgsql/9.3/data/pg_hba.conf</code>.
</p><p>
Assuming Kea is running on the same host as PostgreSQL,
adding lines similar to following should be sufficient to
provide password-authenticated access to Kea's database:
</p><pre class="screen">
local <em class="replaceable"><code>database-name</code></em> <em class="replaceable"><code>user-name</code></em> password
host <em class="replaceable"><code>database-name</code></em> <em class="replaceable"><code>user-name</code></em> 127.0.0.1/32 password
host <em class="replaceable"><code>database-name</code></em> <em class="replaceable"><code>user-name</code></em> ::1/128 password
</pre><p>
</p><p>
These edits are primarily intended as a starting point
not a definitive reference on PostgreSQL administration or
database security. Please consult your PostgreSQL user
manual before making these changes as they may expose
other databases that you run. It may be necessary to
restart PostgreSQL in order for these changes to take effect.
</p></li></ol></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp51977440"></a>4.3.3.2. Initialize the PostgreSQL Database Using kea-admin</h4></div></div></div><p>
If you elected not to create the tables manually, you can do
so now by running the <span class="command"><strong>kea-admin</strong></span> tool:
</p><pre class="screen">
$ <strong class="userinput"><code>kea-admin lease-init pgsql -u <em class="replaceable"><code>database-user</code></em> -p <em class="replaceable"><code>database-password</code></em> -n <em class="replaceable"><code>database-name</code></em></code></strong>
</pre><p>
Do not do this if you already created the tables in manually.
<span class="command"><strong>kea-admin</strong></span> implements rudimentary checks:
it will refuse to initialize a database that contains any
existing tables. If you want to start from scratch, you
must remove all data manually. (This process is a manual
operation on purpose to avoid possibly irretrievable mistakes
by <span class="command"><strong>kea-admin</strong></span>.)
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="pgsql-upgrade"></a>4.3.3.3. Upgrading a PostgreSQL Database from an Earlier Version of Kea</h4></div></div></div><p>
Currently, PostgreSQL only supports Kea schema version 1.0 so no upgrades
are available. As upgrades become available, <span class="command"><strong>kea-admin</strong></span>
will support them.
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51986896"></a>4.3.4. Limitations related to the use of the SQL databases</h3></div></div></div><p>
The lease expiration time is stored in the SQL database for each lease
as a timestamp value. Kea developers observed that MySQL database doesn't
accept timestamps beyond 2147483647 seconds (maximum signed 32-bit number)
from the beginning of the epoch. At the same time, some versions of PostgreSQL
do accept greater values but the value is altered when it is read back.
For this reason the lease database backends put the restriction for the
maximum timestamp to be stored in the database, which is equal to the
maximum signed 32-bit number. This effectively means that the current
Kea version can't store the leases which expiration time is later than
2147483647 seconds since the beginning of the epoch (around year 2038).
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="kea-config"></a>Chapter 5. Kea configuration</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#json-backend">5.1. JSON configuration backend</a></span></dt><dd><dl><dt><span class="section"><a href="#json-format">5.1.1. JSON syntax</a></span></dt><dt><span class="section"><a href="#idp53045488">5.1.2. Simplified Notation</a></span></dt></dl></dd></dl></div><p>Kea is designed to allow different methods by which it can be
configured, each method being implemented by a component known as a
configuration backend. At present, only one such backend is
available, that allowing configuration by means of a JSON file.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="json-backend"></a>5.1. JSON configuration backend</h2></div></div></div><p>JSON is the default configuration backend.
It assumes that the servers are started from the command line
(either directly or using a script, e.g. <code class="filename">keactrl</code>).
The JSON backend uses certain signals to influence Kea. The
configuration file is specified upon startup using the -c parameter.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="json-format"></a>5.1.1. JSON syntax</h3></div></div></div><p>Configuration files for DHCPv4, DHCPv6 and DDNS modules are defined
in an extended JSON format. Basic JSON is defined in <a class="ulink" href="http://tools.ietf.org/html/rfc4627" target="_top">RFC 4627</a>. Kea components
use a slightly modified JSON, in that they allow shell-style
comments in the file: lines with the hash (#) character in the first column
are comment lines and are ignored.</p><p>The configuration file consists of a single object (often colloquially
called a map) started with a curly bracket. It comprises the "Dhcp4", "Dhcp6",
"DhcpDdns" and/or "Logging" objects. It is possible to define additional
elements, but they will be ignored. For example, it is possible to define
Dhcp4, Dhcp6 and Logging elements in a single configuration file that can
be used to start both the DHCPv4 and DHCPv6 components. When starting,
the DHCPv4 component will use Dhcp4 object to configure itself and the
Logging object to configure logging parameters; it will ignore the Dhcp6
object.</p><p>For example, a very simple configuration for both DHCPv4 and DHCPv6
could look like this:
</p><pre class="screen">
# The whole configuration starts here.
{
# DHCPv4 specific configuration starts here.
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth0" ],
"dhcp-socket-type": "raw"
},
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"subnet4": [{
"pools": [ { "pool": "192.0.2.1-192.0.2.200" } ],
"subnet": "192.0.2.0/24"
}],
...
},
# DHCPv4 specific configuration ends here.
# DHCPv6 specific configuration starts here.
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eth1" ]
},
"preferred-lifetime": 3000,
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"subnet6": [{
"pools": [ { "pool": "2001:db8::/80" } ],
"subnet": "2001:db8::/64"
}],
...
},
# DHCPv6 specific configuration ends here.
# Logger parameters (that could be shared among several components) start here.
# This section is used by both the DHCPv4 and DHCPv6 servers.
"Logging": {
"loggers": [{
"name": "*",
"severity": "DEBUG"
}],
...
}
# Logger parameters end here.
# The whole configuration structure ends here.
}
</pre><p>
</p><p>More examples are available in the installed
<code class="filename">share/doc/kea/examples</code> directory.</p><p>To avoid repetition of mostly similar structures, examples in the
rest of this guide will showcase only the subset of parameters appropriate for a given
context. For example, when discussing the IPv6 subnets configuration in
DHCPv6, only subnet6 parameters will be mentioned. It is implied that
the remaining elements (the global map that holds Dhcp6, Logging and possibly
DhcpDdns) are present, but they are omitted for clarity. Usually, locations
where extra parameters may appear are denoted with an ellipsis.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp53045488"></a>5.1.2. Simplified Notation</h3></div></div></div><p>It is sometimes convenient to refer to a specific element in the
configuration hierarchy. Each hierarchy level is separated by a slash.
If there is an array, a specific instance within that array is referenced by
a number in square brackets (with numbering starting at zero). For example, in the above configuration the
valid-lifetime in the Dhcp6 component can be referred to as
Dhcp6/valid-lifetime and the pool in the first subnet defined in the DHCPv6
configuration as Dhcp6/subnet6[0]/pool.</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="keactrl"></a>Chapter 6. Managing Kea with keactrl</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#keactrl-overview">6.1. Overview</a></span></dt><dt><span class="section"><a href="#keactrl-usage">6.2. Command Line Options</a></span></dt><dt><span class="section"><a href="#keactrl-config-file">6.3. The keactrl Configuration File</a></span></dt><dt><span class="section"><a href="#keactrl-commands">6.4. Commands</a></span></dt><dt><span class="section"><a href="#keactrl-overriding-servers">6.5. Overriding the Server Selection</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="keactrl-overview"></a>6.1. Overview</h2></div></div></div><p>keactrl is a shell script which controls the startup, shutdown
and reconfiguration of the Kea servers (<span class="command"><strong>kea-dhcp4</strong></span>,
<span class="command"><strong>kea-dhcp6</strong></span> and <span class="command"><strong>kea-dhcp-ddns</strong></span>). It
also provides the means for checking the current status of the servers
and determining the configuration files in use.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="keactrl-usage"></a>6.2. Command Line Options</h2></div></div></div><p><span class="command"><strong>keactrl</strong></span> is run as follows:
</p><pre class="screen">
keactrl <command> [-c keactrl-config-file] [-s server[,server,..]]
</pre><p>
</p><p>
<span class="command"><strong><command></strong></span> is the one of the commands
described in <a class="xref" href="#keactrl-commands" title="6.4. Commands">Section 6.4, “Commands”</a>.
</p><p>
The optional <span class="command"><strong>-c keactrl-config-file</strong></span> switch
allows specification of an alternate <span class="command"><strong>keactrl</strong></span>
configuration file. (<span class="command"><strong>--ctrl-config</strong></span> is a synonym for
<span class="command"><strong>-c</strong></span>.) In the absence of <span class="command"><strong>-c</strong></span>,
<span class="command"><strong>keactrl</strong></span> will use the default configuration
file <code class="filename">[kea-install-dir]/etc/kea/keactrl.conf</code>.
</p><p>
The optional <span class="command"><strong>-s server[,server ...]</strong></span> switch selects
the servers to which the command is issued.
(<span class="command"><strong>--server</strong></span> is a synonym for <span class="command"><strong>-s</strong></span>.)
If absent, the command is sent to all servers enabled in the keactrl
configuration file.
If multiple servers are specified, they
should be separated by commas with no intervening spaces.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="keactrl-config-file"></a>6.3. The keactrl Configuration File</h2></div></div></div><p>
Depending on requirements, not all of the available servers need
be run. The keactrl configuration file sets which servers are
enabled and which are disabled. The default configuration
file is <code class="filename">[kea-install-dir]/etc/kea/keactrl.conf</code>,
but this can be overridden on a per-command basis using the
<span class="command"><strong>-c</strong></span> switch.
</p><p>
The contents of <code class="filename">keactrl.conf</code> are:
</p><pre class="screen">
# This is a configuration file for keactrl script which controls
# the startup, shutdown, reconfiguration and gathering the status
# of the Kea servers.
# prefix holds the location where the Kea is installed.
prefix=/usr/local
# Location of Kea configuration file.
kea_config_file=${prefix}/etc/kea/kea.conf
# Location of Kea binaries.
exec_prefix=${prefix}
dhcp4_srv=${exec_prefix}/sbin/kea/kea-dhcp4
dhcp6_srv=${exec_prefix}/sbin/kea/kea-dhcp6
dhcp_ddns_srv=${exec_prefix}/sbin/kea/kea-dhcp-ddns
# Start DHCPv4 server?
dhcp4=yes
# Start DHCPv6 server?
dhcp6=yes
# Start DHCP DDNS server?
dhcp_ddns=yes
# Be verbose?
kea_verbose=no
</pre><p>
</p><p>
The <em class="parameter"><code>dhcp4</code></em>, <em class="parameter"><code>dhcp6</code></em> and
<em class="parameter"><code>dhcp_ddns</code></em> parameters set to "yes" configure
<span class="command"><strong>keactrl</strong></span> to manage (start, reconfigure) all servers,
i.e. <span class="command"><strong>kea-dhcp4</strong></span>, <span class="command"><strong>kea-dhcp6</strong></span> and
<span class="command"><strong>kea-dhcp-ddns</strong></span>. When any of these parameters is set to
"no" the <span class="command"><strong>keactrl</strong></span> will ignore
the corresponding server when starting or reconfiguring Kea.
</p><p>
By default, Kea servers managed by <span class="command"><strong>keactrl</strong></span> are
located in <code class="filename">[kea-install-dir]/sbin</code>. This
should work for most installations. If the default
location needs to be altered for any reason, the paths
specified with the <em class="parameter"><code>dhcp4_srv</code></em>,
<em class="parameter"><code>dhcp6_srv</code></em> and <em class="parameter"><code>dhcp_ddns_srv</code></em>
parameters should be modified.
</p><p>
The <em class="parameter"><code>kea_verbose</code></em> parameter specifies the verbosity
of the servers being started. When <em class="parameter"><code>kea_verbose</code></em>
is set to "yes" the logging level of the server is set to DEBUG.
Otherwise, the default logging level is used.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
The verbosity for the server is set when it is started. Once
started, the verbosity can be only changed by stopping the server and
starting it again with the new value of the
<em class="parameter"><code>kea_verbose</code></em> parameter.
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="keactrl-commands"></a>6.4. Commands</h2></div></div></div><p>The following commands are supported by <span class="command"><strong>keactrl</strong></span>
to perform specific operations on the Kea servers:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>start</strong></span> - starts selected servers.
</li><li class="listitem">
<span class="command"><strong>stop</strong></span> - stops all running servers.
</li><li class="listitem">
<span class="command"><strong>reload</strong></span> - triggers reconfiguration of the
selected servers by sending the SIGHUP signal to them.
</li><li class="listitem">
<span class="command"><strong>status</strong></span> - returns the status of the servers (active
or inactive) and the names of the configuration files in use.
</li></ul></div><p>
</p><p>Typical output from <span class="command"><strong>keactrl</strong></span> when starting
the servers looks similar to the following:
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl start</code></strong>
INFO/keactrl: Starting kea-dhcp4 -c /usr/local/etc/kea/kea.conf -d
INFO/keactrl: Starting kea-dhcp6 -c /usr/local/etc/kea/kea.conf -d
INFO/keactrl: Starting kea-dhcp-ddns -c /usr/local/etc/kea/kea.conf -d
</pre><p>
</p><p>Kea's servers create PID files upon startup. These files are used
by keactrl to determine whether or not a given server is running. If
one or more servers are running when the start command is issued, the
output will look similar to the following:
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl start</code></strong>
INFO/keactrl: kea-dhcp4 appears to be running, see: PID 10918, PID file: /usr/local/var/kea/kea.kea-dhcp4.pid.
INFO/keactrl: kea-dhcp6 appears to be running, see: PID 10924, PID file: /usr/local/var/kea/kea.kea-dhcp6.pid.
INFO/keactrl: kea-dhcp-ddns appears to be running, see: PID 10930, PID file: /usr/local/var/kea/kea.kea-dhcp-ddns.pid.
</pre><p>
During normal shutdowns these PID files are deleted. They may, however,
be left over as remnants following a system crash. It is possible,
though highly unlikely, that upon system restart the PIDs they contain
actually refer to processes unrelated to Kea. This condition will cause
keactrl to decide that the servers are running, when in fact they are
not. In such a case the PID files as listed in the keactrl output
must be manually deleted.
</p><p>The following command stops all servers:
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl stop</code></strong>
INFO/keactrl: Stopping kea-dhcp4...
INFO/keactrl: Stopping kea-dhcp6...
INFO/keactrl: Stopping kea-dhcp-ddns...
</pre><p>
Note that the <span class="command"><strong>stop</strong></span> will attempt to stop all servers
regardless of whether they are "enabled" in the <code class="filename">keactrl.conf</code>.
If any of the servers are not running, an informational message
is displayed as in the <span class="command"><strong>stop</strong></span> command output below.
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl stop</code></strong>
INFO/keactrl: kea-dhcp4 isn't running.
INFO/keactrl: kea-dhcp6 isn't running.
INFO/keactrl: kea-dhcp-ddns isn't running.
</pre><p>
</p><p>
As already mentioned, the reconfiguration of each Kea server is
triggered by the SIGHUP signal. The <span class="command"><strong>reload</strong></span>
command sends the SIGHUP signal to the servers that are enabled in
the <span class="command"><strong>keactrl</strong></span> configuration file and are
currently running. When a server receives the SIGHUP signal it
re-reads its configuration file and, if the new configuration is
valid, uses the new configuration. A reload is executed as follows:
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl reload</code></strong>
INFO/keactrl: Reloading kea-dhcp4...
INFO/keactrl: Reloading kea-dhcp6...
INFO/keactrl: Reloading kea-dhcp-ddns...
</pre><p>
If any of the servers are not running, an informational message
is displayed as in the <span class="command"><strong>reload</strong></span> command output below.
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl stop</code></strong>
INFO/keactrl: kea-dhcp4 isn't running.
INFO/keactrl: kea-dhcp6 isn't running.
INFO/keactrl: kea-dhcp-ddns isn't running.
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Currently <span class="command"><strong>keactrl</strong></span> does not report configuration
failures when the server is started or reconfigured. To check if
the server's configuration succeeded the Kea log must be examined
for errors. By default, this is written to the syslog file.
</p></div><p>
Sometimes it is useful to check which servers are running. The
<span class="command"><strong>status</strong></span> reports this, typical output looking like:
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl status</code></strong>
DHCPv4 server: active
DHCPv6 server: inactive
DHCP DDNS: active
Kea configuration file: /usr/local/etc/kea/kea.conf
keactrl configuration file: /usr/local/etc/kea/keactrl.conf
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="keactrl-overriding-servers"></a>6.5. Overriding the Server Selection</h2></div></div></div><p>
The optional <span class="command"><strong>-s</strong></span> switch allows
the selection of the servers to which <span class="command"><strong>keactrl</strong></span>
command is issued. For example, the following
instructs <span class="command"><strong>keactrl</strong></span> to stop the
<span class="command"><strong>kea-dhcp4</strong></span> and <span class="command"><strong>kea-dhcp6</strong></span> servers
and leave the <span class="command"><strong>kea-dhcp-ddns</strong></span> server running:
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl stop -s dhcp4,dhcp6</code></strong>
</pre><p>
</p><p>
Similarly, the following
will only start the <span class="command"><strong>kea-dhcp4</strong></span> and
<span class="command"><strong>kea-dhcp-ddns</strong></span> servers and not
<span class="command"><strong>kea-dhcp6</strong></span>.
</p><pre class="screen">
<strong class="userinput"><code>$ keactrl start -s dhcp4,dhcp_ddns</code></strong>
</pre><p>
</p><p>
Note that the behavior of the <span class="command"><strong>-s</strong></span> switch
with the <span class="command"><strong>start</strong></span> and <span class="command"><strong>reload</strong></span> commands
is different to its behavior with the <span class="command"><strong>stop</strong></span> command.
On <span class="command"><strong>start</strong></span> and <span class="command"><strong>reload</strong></span>,
<span class="command"><strong>keactrl</strong></span> will check if the servers given as
parameters to the <span class="command"><strong>-s</strong></span> switch are
enabled in the <span class="command"><strong>keactrl</strong></span> configuration file:
if not, the server will be ignored. For <span class="command"><strong>stop</strong></span> however,
this check is not made: the command is applied to all listed servers,
regardless of whether they have been enabled in the file.
</p><p>
The following keywords can be used with the <span class="command"><strong>-s</strong></span>
command line option:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>dhcp4</strong></span> for <span class="command"><strong>kea-dhcp4.</strong></span>
</li><li class="listitem">
<span class="command"><strong>dhcp6</strong></span> for <span class="command"><strong>kea-dhcp6.</strong></span>
</li><li class="listitem">
<span class="command"><strong>dhcp_ddns</strong></span> for <span class="command"><strong>kea-dhcp-ddns.</strong></span>
</li><li class="listitem">
<span class="command"><strong>all</strong></span> for all servers (default).
</li></ul></div><p>
</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="dhcp4"></a>Chapter 7. The DHCPv4 Server</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#dhcp4-start-stop">7.1. Starting and Stopping the DHCPv4 Server</a></span></dt><dt><span class="section"><a href="#dhcp4-configuration">7.2. DHCPv4 Server Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54262112">7.2.1. Introduction</a></span></dt><dt><span class="section"><a href="#idp54498048">7.2.2. Lease Storage</a></span></dt><dt><span class="section"><a href="#idp54960688">7.2.3. Hosts Storage</a></span></dt><dt><span class="section"><a href="#dhcp4-interface-configuration">7.2.4. Interface configuration</a></span></dt><dt><span class="section"><a href="#dhcpinform-unicast-issues">7.2.5. Issues with unicast responses to DHCPINFORM</a></span></dt><dt><span class="section"><a href="#ipv4-subnet-id">7.2.6. IPv4 Subnet Identifier</a></span></dt><dt><span class="section"><a href="#dhcp4-address-config">7.2.7. Configuration of IPv4 Address Pools</a></span></dt><dt><span class="section"><a href="#dhcp4-std-options">7.2.8. Standard DHCPv4 options</a></span></dt><dt><span class="section"><a href="#dhcp4-custom-options">7.2.9. Custom DHCPv4 options</a></span></dt><dt><span class="section"><a href="#dhcp4-vendor-opts">7.2.10. DHCPv4 Vendor Specific Options</a></span></dt><dt><span class="section"><a href="#dhcp4-option-spaces">7.2.11. Nested DHCPv4 Options (Custom Option Spaces)</a></span></dt><dt><span class="section"><a href="#dhcp4-option-data-defaults">7.2.12. Unspecified parameters for DHCPv4 option configuration</a></span></dt><dt><span class="section"><a href="#dhcp4-stateless-configuration">7.2.13. Stateless Configuration of DHCPv4 clients</a></span></dt><dt><span class="section"><a href="#dhcp4-client-classifier">7.2.14. Client Classification in DHCPv4</a></span></dt><dt><span class="section"><a href="#dhcp4-ddns-config">7.2.15. Configuring DHCPv4 for DDNS</a></span></dt><dt><span class="section"><a href="#dhcp4-next-server">7.2.16. Next Server (siaddr)</a></span></dt><dt><span class="section"><a href="#dhcp4-echo-client-id">7.2.17. Echoing Client-ID (RFC 6842)</a></span></dt><dt><span class="section"><a href="#dhcp4-match-client-id">7.2.18. Using Client Identifier and Hardware Address</a></span></dt></dl></dd><dt><span class="section"><a href="#host-reservation-v4">7.3. Host reservation in DHCPv4</a></span></dt><dd><dl><dt><span class="section"><a href="#reservation4-types">7.3.1. Address reservation types</a></span></dt><dt><span class="section"><a href="#reservation4-conflict">7.3.2. Conflicts in DHCPv4 reservations</a></span></dt><dt><span class="section"><a href="#reservation4-hostname">7.3.3. Reserving a hostname</a></span></dt><dt><span class="section"><a href="#reservation4-options">7.3.4. Reserving specific options</a></span></dt><dt><span class="section"><a href="#reservation4-mode">7.3.5. Fine Tuning IPv4 Host Reservation</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp4-serverid">7.4. Server Identifier in DHCPv4</a></span></dt><dt><span class="section"><a href="#dhcp4-subnet-selection">7.5. How the DHCPv4 Server Selects a Subnet for the Client</a></span></dt><dd><dl><dt><span class="section"><a href="#dhcp4-relay-override">7.5.1. Using a Specific Relay Agent for a Subnet</a></span></dt><dt><span class="section"><a href="#dhcp4-srv-example-client-class-relay">7.5.2. Segregating IPv4 Clients in a Cable Network</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp4-decline">7.6. Duplicate Addresses (DHCPDECLINE support)</a></span></dt><dt><span class="section"><a href="#dhcp4-stats">7.7. Statistics in DHCPv4 server</a></span></dt><dt><span class="section"><a href="#dhcp4-ctrl-channel">7.8. Management API for the DHCPv4 server</a></span></dt><dt><span class="section"><a href="#dhcp4-std">7.9. Supported DHCP Standards</a></span></dt><dt><span class="section"><a href="#dhcp4-limit">7.10. DHCPv4 Server Limitations</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-start-stop"></a>7.1. Starting and Stopping the DHCPv4 Server</h2></div></div></div><p>
It is recommended that the Kea DHCPv4 server be started and stopped
using <span class="command"><strong>keactrl</strong></span> (described in <a class="xref" href="#keactrl" title="Chapter 6. Managing Kea with keactrl">Chapter 6, <i>Managing Kea with keactrl</i></a>).
However, it is also possible to run the server directly: it accepts
the following command-line switches:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>-c <em class="replaceable"><code>file</code></em></strong></span> -
specifies the configuration file. This is the only mandatory
switch.</li><li class="listitem">
<span class="command"><strong>-d</strong></span> - specifies whether the server
logging should be switched to debug/verbose mode. In verbose mode,
the logging severity and debuglevel specified in the configuration
file are ignored and "debug" severity and the maximum debuglevel
(99) are assumed. The flag is convenient, for temporarily
switching the server into maximum verbosity, e.g. when
debugging.</li><li class="listitem">
<span class="command"><strong>-p <em class="replaceable"><code>port</code></em></strong></span> -
specifies UDP port the server will listen on. This is only
useful during testing, as the DHCPv4 server listening on
ports other than default DHCPv4 ports will not be able to
handle regular DHCPv4 queries.</li><li class="listitem">
<span class="command"><strong>-v</strong></span> - prints out Kea version and exits.
</li><li class="listitem">
<span class="command"><strong>-V</strong></span> - prints out Kea extended version with
additional parameters and exits.
</li><li class="listitem">
<span class="command"><strong>-W</strong></span> - prints out Kea configuration report
and exits.
</li></ul></div><p>
The <span class="command"><strong>-V</strong></span> command returns the versions of the
external libraries dynamically linked.
</p><p>
The <span class="command"><strong>-W</strong></span> command describes the environment used
to build Kea. This command displays a copy of the
<code class="filename">config.report</code> file produced by
<strong class="userinput"><code>./configure</code></strong> that is embedded in the
executable binary.
</p><p>
The <code class="filename">config.report</code> may also be accessed more
directly. The following command may be used to extract this
information. The binary <strong class="userinput"><code>path</code></strong> may be found
in the install directory or in the <code class="filename">.libs</code>
subdirectory in the source tree. For example
<code class="filename">kea/src/bin/dhcp4/.libs/kea-dhcp4</code>.
</p><pre class="screen">
strings <strong class="userinput"><code>path</code></strong>/kea-dhcp4 | sed -n 's/;;;; //p'
</pre><p>
</p><p>
When running in a console, the server can be shut down by
pressing ctrl-c. It detects the key combination and shuts
down gracefully.
</p><p>
On start-up, the server will detect available network interfaces
and will attempt to open UDP sockets on all interfaces
mentioned in the configuration file.
</p><p>
Since the DHCPv4 server opens privileged ports, it requires root
access. Make sure you run this daemon as root.
</p><p>
During startup the server will attempt to create a PID file of the
form: [localstatedir]/[conf name].kea-dhcp4.pid
where:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>localstatedir</strong></span>: The value as passed into the
build configure script. It defaults to "/usr/local/var". Note
that this value may be overridden at run time by setting the environment
variable KEA_PIDFILE_DIR. This is intended primarily for testing purposes.
</li><li class="listitem"><span class="command"><strong>conf name</strong></span>: The configuration file name
used to start the server, minus all preceding path and file extension.
For example, given a pathname of "/usr/local/etc/kea/myconf.txt", the
portion used would be "myconf".
</li></ul></div><p>
If the file already exists and contains the PID of a live process,
the server will issue a DHCP4_ALREADY_RUNNING log message and exit. It
is possible, though unlikely, that the file is a remnant of a system crash
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-configuration"></a>7.2. DHCPv4 Server Configuration</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54262112"></a>7.2.1. Introduction</h3></div></div></div><p>
This section explains how to configure the DHCPv4 server using the
Kea configuration backend. (Kea configuration using any other
backends is outside of scope of this document.) Before DHCPv4
is started, its configuration file has to be created. The
basic configuration is as follows:
</p><pre class="screen">
{
# DHCPv4 configuration starts in this line
"Dhcp4": {
# First we set up global values
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
# Next we setup the interfaces to be used by the server.
"interfaces-config": {
"interfaces": [ "eth0" ]
},
# And we specify the type of lease database
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/var/kea/dhcp4.leases"
},
# Finally, we list the subnets from which we will be leasing addresses.
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{ "pool": "192.0.2.1 - 192.0.2.200" }
]
}
]
# DHCPv4 configuration ends with this line
}
} </pre><p>
</p><p>The following paragraphs provide a brief overview of the parameters in
the above example and
their format. Subsequent sections of this chapter go into much greater detail
for these and other parameters.</p><p>The lines starting with a hash (#) are comments and are ignored by
the server; they do not impact its
operation in any way.</p><p>The configuration starts in the first line with the initial
opening curly bracket (or brace). Each configuration consists of
one or more objects. In this specific example, we have only one
object called Dhcp4. This is a simplified configuration, as usually
there will be additional objects, like <span class="command"><strong>Logging</strong></span> or
<span class="command"><strong>DhcpDns</strong></span>, but we omit them now for clarity. The Dhcp4
configuration starts with the <span class="command"><strong>"Dhcp4": {</strong></span> line
and ends with the corresponding closing brace (in the above example,
the brace after the last comment). Everything defined between those
lines is considered to be the Dhcp4 configuration.</p><p>In the general case, the order in which those parameters appear does not
matter. There are two caveats here though. The first one is to remember that
the configuration file must be well formed JSON. That means that the parameters
for any given scope must be separated by a comma and there must not be a comma
after the last parameter. When reordering a configuration file, keep in mind that
moving a parameter to or from the last position in a given scope may also require
moving the comma. The second caveat is that it is uncommon — although
legal JSON — to
repeat the same parameter multiple times. If that happens, the last occurrence of a
given parameter in a given scope is used while all previous instances are
ignored. This is unlikely to cause any confusion as there are no real life
reasons to keep multiple copies of the same parameter in your configuration
file.</p><p>Moving onto the DHCPv4 configuration elements, the very first few elements
define some global parameters. <span class="command"><strong>valid-lifetime</strong></span> defines for how long the addresses (leases) given out by the
server are valid. If nothing changes, a client that got an address is allowed to
use it for 4000 seconds. (Note that integer numbers are specified as is,
without any quotes around them.) <span class="command"><strong>renew-timer</strong></span> and
<span class="command"><strong>rebind-timer</strong></span> are values that
define T1 and T2 timers that govern when the client will begin the renewal and
rebind procedures. Note that <span class="command"><strong>renew-timer</strong></span> and
<span class="command"><strong>rebind-timer</strong></span> are optional. If they are not specified the
client will select values for T1 and T2 timers according to the
<a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>.</p><p>The <span class="command"><strong>interfaces-config</strong></span> map specifies the server
configuration concerning the network interfaces, on which the server should
listen to the DHCP messages. The <span class="command"><strong>interfaces</strong></span> parameter
specifies a list of network interfaces on which the server should listen.
Lists are opened and closed with square brackets, with elements separated
by commas. Had we wanted to listen on two interfaces, the
<span class="command"><strong>interfaces-config</strong></span> would look like this:
</p><pre class="screen">
"interfaces-config": {
"interfaces": [ "eth0", "eth1" ]
},
</pre><p>
</p><p>The next couple of lines define the lease database, the place where the server
stores its lease information. This particular example tells the server to use
<span class="command"><strong>memfile</strong></span>, which is the simplest (and fastest) database
backend. It uses an in-memory database and stores leases on disk in a CSV
file. This is a very simple configuration. Usually, lease database configuration
is more extensive and contains additional parameters. Note that
<span class="command"><strong>lease-database</strong></span>
is an object and opens up a new scope, using an opening brace.
Its parameters (just one in this example -- <span class="command"><strong>type</strong></span>)
follow. Had there been more than one, they would be separated by commas. This
scope is closed with a closing brace. As more parameters follow, a trailing
comma is present.</p><p>Finally, we need to define a list of IPv4 subnets. This is the
most important DHCPv4 configuration structure as the server uses that
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
specified with the <span class="command"><strong>subnet4</strong></span> parameter. It is a list,
so it starts and ends with square brackets. Each subnet definition in
the list has several attributes associated with it, so it is a structure
and is opened and closed with braces. At a minimum, a subnet definition
has to have at least two parameters: <span class="command"><strong>subnet</strong></span> (that
defines the whole subnet) and <span class="command"><strong>pools</strong></span> (which is a list of
dynamically allocated pools that are governed by the DHCP server).</p><p>The example contains a single subnet. Had more than one been defined,
additional elements
in the <span class="command"><strong>subnet4</strong></span> parameter would be specified and
separated by commas. For example, to define three subnets, the following
syntax would be used:
</p><pre class="screen">
"subnet4": [
{
"pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
"subnet": "192.0.2.0/24"
},
{
"pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
"subnet": "192.0.3.0/24"
},
{
"pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
"subnet": "192.0.4.0/24"
}
]
</pre><p>
</p><p>After all parameters are specified, we have two contexts open:
global and Dhcp4, hence we need two closing curly brackets to close them.
In a real life configuration file there most likely would be additional
components defined such as Logging or DhcpDdns, so the closing brace would
be followed by a comma and another object definition.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54498048"></a>7.2.2. Lease Storage</h3></div></div></div><p>All leases issued by the server are stored in the lease database.
Currently there are three database backends available:
memfile (which is the default backend), MySQL and PostgreSQL.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54499408"></a>7.2.2.1. Memfile, Basic Storage for Leases</h4></div></div></div><p>The server is able to store lease data in different repositories. Larger
deployments may elect to store leases in a database. <a class="xref" href="#database-configuration4" title="7.2.2.2. Lease Database Configuration">Section 7.2.2.2, “Lease Database Configuration”</a> describes this option. In typical
smaller deployments though, the server will use a CSV file rather than a database to
store lease information. As well as requiring less administration, an
advantage of using a file for storage is that it
eliminates a dependency on third-party database software.</p><p>The configuration of the file backend (Memfile) is controlled through
the Dhcp4/lease-database parameters. The <span class="command"><strong>type</strong></span> parameter
is mandatory and it specifies which storage for leases the server should use.
The value of <strong class="userinput"><code>"memfile"</code></strong> indicates that the file should
be used as the storage. The following list presents the remaining, not mandatory
parameters, which can be used to configure the Memfile backend.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>persist</strong></span>: controls whether the new leases and
updates to existing leases are written to the file. It is strongly
recommended that the value of this parameter is set to
<strong class="userinput"><code>true</code></strong> at all times, during the server's normal
operation. Not writing leases to disk will mean that if a server is restarted
(e.g. after a power failure), it will not know what addresses have been
assigned. As a result, it may hand out addresses to new clients that are
already in use. The value of <strong class="userinput"><code>false</code></strong> is mostly useful
for performance testing purposes. The default value of the
<span class="command"><strong>persist</strong></span> parameter is <strong class="userinput"><code>true</code></strong>,
which enables writing lease updates
to the lease file.
</li><li class="listitem"><span class="command"><strong>name</strong></span>: specifies an absolute location of the lease
file in which new leases and lease updates will be recorded. The default value
for this parameter is <strong class="userinput"><code>"[kea-install-dir]/var/kea/kea-leases4.csv"
</code></strong>.</li><li class="listitem"><span class="command"><strong>lfc-interval</strong></span>: specifies the interval in seconds, at
which the server (Memfile backend) will perform a lease file cleanup (LFC),
which removes the redundant (historical) information from the lease file
and effectively reduces the lease file size. The cleanup process is described
in more detailed fashion further in this section. The default value of the
<span class="command"><strong>lfc-interval</strong></span> is <strong class="userinput"><code>0</code></strong>, which disables
the LFC.</li></ul></div><p>
</p><p>The example configuration of the Memfile backend is presented below:
</p><pre class="screen">
"Dhcp4": {
"lease-database": {
<strong class="userinput"><code>"type": "memfile"</code></strong>,
<strong class="userinput"><code>"persist": true</code></strong>,
<strong class="userinput"><code>"name": "/tmp/kea-leases4.csv",</code></strong>
<strong class="userinput"><code>"lfc-interval": 1800</code></strong>
}
}
</pre><p>
This configuration selects the <code class="filename">/tmp/kea-leases4.csv</code> as
the storage for lease information and enables persistence (writing lease updates
to this file). It also configures the backend perform the periodic cleanup
of the lease files, executed every 30 minutes.
</p><p>It is important to know how the lease file contents are organized
to understand why the periodic lease file cleanup is needed. Every time when
the server updates a lease or creates a new lease for the client, the new
lease information must be recorded in the lease file. For performance reasons,
the server does not supersede the existing client's lease, as it would require
the lookup of the specific lease entry, but simply appends the new lease
information at the end of the lease file. The previous lease entries for the
client are not removed. When the server loads leases from the lease file, e.g.
at the server startup, it assumes that the latest lease entry for the client
is the valid one. The previous entries are discarded. This means that the
server can re-construct the accurate information about the leases even though
there may be many lease entries for each client. However, storing many entries
for each client results in bloated lease file and impairs the performance of
the server's startup and reconfiguration, as it needs to process larger number
of lease entries.
</p><p>The lease file cleanup removes all previous entries for each client and
leaves only the latest ones. The interval at which the cleanup is performed
is configurable, and it should be selected according to the frequency of lease
renewals initiated by the clients. The more frequent renewals are, the lesser
value of the <span class="command"><strong>lfc-interval</strong></span> should be. Note however, that the
LFC takes time and thus it is possible (although unlikely) that new cleanup
is started while the previous cleanup instance is still running, if the
<span class="command"><strong>lfc-interval</strong></span> is too short. The server would recover from
this by skipping the new cleanup when it detects that the previous cleanup
is still in progress. But, this implies that the actual cleanups will be
triggered more rarely than configured. Moreover, triggering a new cleanup
adds an overhead to the server, which will not be able to respond to new
requests for a short period of time when the new cleanup process is spawned.
Therefore, it is recommended that the <span class="command"><strong>lfc-interval</strong></span> value
is selected in a way that would allow for completing the cleanup before the
new cleanup is triggered.
</p><p>The LFC is performed by a separate process (in background) to avoid
performance impact on the server process. In order to avoid the conflicts
between the two processes both using the same lease files, the LFC process
operates on the copy of the original lease file, rather than on the lease
file used by the server to record lease updates. There are also other files
being created as a side effect of the lease file cleanup. The detailed
description of the LFC is located on the Kea wiki:
<a class="ulink" href="http://kea.isc.org/wiki/LFCDesign" target="_top">http://kea.isc.org/wiki/LFCDesign</a>.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="database-configuration4"></a>7.2.2.2. Lease Database Configuration</h4></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Lease database access information must be configured for the DHCPv4 server,
even if it has already been configured for the DHCPv6 server. The servers
store their information independently, so each server can use a separate
database or both servers can use the same database.</p></div><p>Lease database configuration is controlled through the Dhcp4/lease-database
parameters. The type of the database must be set to "memfile", "mysql" or "postgresql",
e.g.
</p><pre class="screen">
"Dhcp4": { "lease-database": { <strong class="userinput"><code>"type": "mysql"</code></strong>, ... }, ... }
</pre><p>
Next, the name of the database to hold the leases must be set: this is the
name used when the lease database was created (see <a class="xref" href="#mysql-database-create" title="4.3.2.1. First Time Creation of Kea Database">Section 4.3.2.1, “First Time Creation of Kea Database”</a>
or <a class="xref" href="#pgsql-database-create" title="4.3.3.1. Manually Create the PostgreSQL Database and the Kea User">Section 4.3.3.1, “Manually Create the PostgreSQL Database and the Kea User”</a>).
</p><pre class="screen">
"Dhcp4": { "lease-database": { <strong class="userinput"><code>"name": "<em class="replaceable"><code>database-name</code></em>" </code></strong>, ... }, ... }
</pre><p>
If the database is located on a different system to the DHCPv4 server, the
database host name must also be specified (although it should be noted that this
configuration may have a severe impact on server performance):
</p><pre class="screen">
"Dhcp4": { "lease-database": { <strong class="userinput"><code>"host": <em class="replaceable"><code>remote-host-name</code></em></code></strong>, ... }, ... }
</pre><p>
The usual state of affairs will be to have the database on the same machine as
the DHCPv4 server. In this case, set the value to the empty string:
</p><pre class="screen">
"Dhcp4": { "lease-database": { <strong class="userinput"><code>"host" : ""</code></strong>, ... }, ... }
</pre><p>
</p><p>Finally, the credentials of the account under which the server will
access the database should be set:
</p><pre class="screen">
"Dhcp4": { "lease-database": { <strong class="userinput"><code>"user": "<em class="replaceable"><code>user-name</code></em>"</code></strong>,
<strong class="userinput"><code>"password": "<em class="replaceable"><code>password</code></em>"</code></strong>,
... },
... }
</pre><p>
If there is no password to the account, set the password to the empty string
"". (This is also the default.)</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54960688"></a>7.2.3. Hosts Storage</h3></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This feature did not undergo the regular system level
testing conducted by ISC. As such, please treat it as
experimental.</p></div><p>Kea is also able to store information about host reservations in the
database. Hosts database configuration uses the same syntax as lease
database. In fact, Kea server opens independent connections for each
purpose, be it lease or hosts information. This gives the solution most
flexibility. Kea can be used to keep leases and host reservations
separately, but can also point to the same database. Currently the only
supported hosts database type is MySQL.</p><p>Please note that usage of hosts storage is optional. User can define
all host reservations in the configuration file. That is the recommended way
if the number of reservations is small. However, with the number of
reservations growing it's more convenient to use host storage. Please note
that both storages (configuration file and MySQL) can be used together. If
hosts are defined in both places, the definitions from configuration file
are checked first and external storage is checked later, if
necessary.</p><p>All hosts leases issued by the server are stored in the hosts
database. Currently there is only one available backend: MySQL. Other host
backends will become available in future Kea versions.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="hosts-database-configuration4"></a>7.2.3.1. IPv4 Hosts Database Configuration</h4></div></div></div><p>Hosts database configuration is controlled through the Dhcp4/hosts-database
parameters. If enabled, the type of the database must be set to "mysql". Other
hosts backends may be added in later Kea versions.
</p><pre class="screen">
"Dhcp4": { "hosts-database": { <strong class="userinput"><code>"type": "mysql"</code></strong>, ... }, ... }
</pre><p>
Next, the name of the database to hold the leases must be set: this is the
name used when the lease database was created (see <a class="xref" href="#mysql-database-create" title="4.3.2.1. First Time Creation of Kea Database">Section 4.3.2.1, “First Time Creation of Kea Database”</a>).
</p><pre class="screen">
"Dhcp4": { "hosts-database": { <strong class="userinput"><code>"name": "<em class="replaceable"><code>database-name</code></em>" </code></strong>, ... }, ... }
</pre><p>
If the database is located on a different system to the DHCPv4 server, the
database host name must also be specified (although it should be noted that this
configuration may have a severe impact on server performance):
</p><pre class="screen">
"Dhcp4": { "hosts-database": { <strong class="userinput"><code>"host": <em class="replaceable"><code>remote-host-name</code></em></code></strong>, ... }, ... }
</pre><p>
The usual state of affairs will be to have the database on the same machine as
the DHCPv4 server. In this case, set the value to the empty string:
</p><pre class="screen">
"Dhcp4": { "hosts-database": { <strong class="userinput"><code>"host" : ""</code></strong>, ... }, ... }
</pre><p>
</p><p>Finally, the credentials of the account under which the server will
access the database should be set:
</p><pre class="screen">
"Dhcp4": { "hosts-database": { <strong class="userinput"><code>"user": "<em class="replaceable"><code>user-name</code></em>"</code></strong>,
<strong class="userinput"><code>"password": "<em class="replaceable"><code>password</code></em>"</code></strong>,
... },
... }
</pre><p>
If there is no password to the account, set the password to the empty string
"". (This is also the default.)</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-interface-configuration"></a>7.2.4. Interface configuration</h3></div></div></div><p>The DHCPv4 server has to be configured to listen on specific network
interfaces. The simplest network interface configuration tells the server to
listen on all available interfaces:
</p><pre class="screen">
"Dhcp4": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"*"</code></strong> ]
}
...
},
</pre><p>
The asterisk plays the role of a wildcard and means "listen on all interfaces".
However, it is usually a good idea to explicitly specify interface names:
</p><pre class="screen">
"Dhcp4": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1", "eth3"</code></strong> ]
},
...
}
</pre><p>
</p><p>It is possible to use wildcard interface name (asterisk) concurrently
with explicit interface names:
</p><pre class="screen">
"Dhcp4": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1", "eth3", "*"</code></strong> ]
},
...
}
</pre><p>
It is anticipated that this form of usage will only be used when it is desired to
temporarily override a list of interface names and listen on all interfaces.
</p><p>Some deployments of the DHCP servers require that the servers listen
on the interfaces with multiple IPv4 addresses configured. In these situations,
the address to use can be selected by appending an IPv4 address to the interface
name in the following manner:
</p><pre class="screen">
"Dhcp4": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1/10.0.0.1", "eth3/192.0.2.3"</code></strong> ]
},
...
}
</pre><p>
</p><p>If it is desired that the server listens on multiple IPv4 addresses assigned
to the same interface, multiple addresses can be specified for this interface
as in the example below:
</p><pre class="screen">
"Dhcp4": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1/10.0.0.1", "eth1/10.0.0.2"</code></strong> ]
},
...
}
</pre><p>
</p><p>Alternatively, if the server should listen on all addresses for the particular
interface, an interface name without any address should be specified.</p><p>Kea supports responding to directly connected clients which don't have
an address configured on the interface yet. This requires that the server
injects the hardware address of the destination into the data link layer
of the packet being sent to the client. The DHCPv4 server utilizes the
raw sockets to achieve this, and builds the entire IP/UDP stack for the
outgoing packets. The down side of raw socket use, however, is that incoming
and outgoing packets bypass the firewalls (e.g. iptables). It is also
troublesome to handle traffic on multiple IPv4 addresses assigned to the
same interface, as raw sockets are bound to the interface and advanced
packet filtering techniques (e.g. using the BPF) have to be used to
receive unicast traffic on the desired addresses assigned to the interface,
rather than capturing whole traffic reaching the interface to which the raw
socket is bound. Therefore, in the deployments where the server doesn't
have to provision the directly connected clients and only receives the
unicast packets from the relay agents, it is desired to configure the
DHCP server to utilize the IP/UDP datagram sockets, instead of raw sockets.
The following configuration demonstrates how this can be achieved:
</p><pre class="screen">
"Dhcp4": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1", "eth3"</code></strong> ],
"dhcp-socket-type": "udp"
},
...
}
</pre><p>
The <span class="command"><strong>dhcp-socket-type</strong></span> specifies that the IP/UDP sockets will
be opened on all interfaces on which the server listens, i.e. "eth1" and
"eth3" in our case. If the <span class="command"><strong>dhcp-socket-type</strong></span> is set to
<strong class="userinput"><code>raw</code></strong>, it configures the server to use raw sockets
instead. If the <span class="command"><strong>dhcp-socket-type</strong></span> value is not specified, the
default value <strong class="userinput"><code>raw</code></strong> is used.
</p><p>Using UDP sockets automatically disables the reception of broadcast
packets from directly connected clients. This effectively means that the
UDP sockets can be used for relayed traffic only. When using the raw sockets,
both the traffic from the directly connected clients and the relayed traffic
will be handled. Caution should be taken when configuring the server to open
multiple raw sockets on the interface with several IPv4 addresses assigned.
If the directly connected client sends the message to the broadcast address
all sockets on this link will receive this message and multiple responses
will be sent to the client. Hence, the configuration with multiple IPv4
addresses assigned to the interface should not be used when the directly
connected clients are operating on that link. To use a single address on
such interface, the "interface-name/address" notation should be used.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Specifying the value <strong class="userinput"><code>raw</code></strong> as the socket type,
doesn't guarantee that the raw sockets will be used! The use of raw sockets
to handle the traffic from the directly connected clients is currently
supported on Linux and BSD systems only. If the raw sockets are not
supported on the particular OS, the server will issue a warning and
fall back to use the IP/UDP sockets.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcpinform-unicast-issues"></a>7.2.5. Issues with unicast responses to DHCPINFORM</h3></div></div></div><p>The use of UDP sockets has certain benefits in deployments
where the server receives only relayed traffic. These benefits are
mentioned in the <a class="xref" href="#dhcp4-interface-configuration" title="7.2.4. Interface configuration">Section 7.2.4, “Interface configuration”</a>. From
the administrator's perspective it is often desired to be able to
configure the system's firewall to filter out the unwanted traffic, and
the use of UDP sockets facilitates it. However, the administrator must
also be aware of the implications related to filtering certain types
of traffic as it may impair the DHCP server's operation.
</p><p>In this section we are focusing on the case when the server
receives the DHCPINFORM message from the client via a relay. According
to the <a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>,
the server should unicast the DHCPACK response to the address carried in
the 'ciaddr' field. When the UDP socket is in use, the DHCP server
relies on the low level functions of an operating system to build the
data link, IP and UDP layers of the outgoing message. Typically, the
OS will first use ARP to obtain the client's link layer address to be
inserted into the frame's header, if the address is not cached from
a previous transaction that the client had with the server.
When the ARP exchange is successful, the DHCP message can be unicast
to the client, using the obtained address.
</p><p>Some system administrators block ARP messages in their network,
which causes issues for the server when it responds to the
DHCPINFORM messages, because the server is unable to send the
DHCPACK if the preceding ARP communication fails. Since the OS is
entirely responsible for the ARP communication and then sending
the DHCP packet over the wire, the DHCP server has no means to
determine that the ARP exchange failed and the DHCP response message
was dropped. Thus, the server does not log any error messages when
the outgoing DHCP response is dropped. At the same time, all hooks
pertaining to the packet sending operation will be called, even
though the message never reaches its destination.
</p><p>Note that the issue described in this section is not observed
when the raw sockets are in use, because, in this case, the DHCP server
builds all the layers of the outgoing message on its own and does not
use ARP. Instead, it inserts the value carried in the 'chaddr' field
of the DHCPINFORM message into the link layer.
</p><p>Server administrators willing to support DHCPINFORM
messages via relays should not block ARP traffic in their
networks or should use raw sockets instead of UDP sockets.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="ipv4-subnet-id"></a>7.2.6. IPv4 Subnet Identifier</h3></div></div></div><p>
The subnet identifier is a unique number associated with a particular subnet.
In principle, it is used to associate clients' leases with their respective subnets.
When a subnet identifier is not specified for a subnet being configured, it will
be automatically assigned by the configuration mechanism. The identifiers
are assigned from 1 and are monotonically increased for each subsequent
subnet: 1, 2, 3 ....
</p><p>
If there are multiple subnets configured with auto-generated identifiers and
one of them is removed, the subnet identifiers may be renumbered. For example:
if there are four subnets and the third is removed the last subnet will be assigned
the identifier that the third subnet had before removal. As a result, the leases
stored in the lease database for subnet 3 are now associated with
subnet 4, something that may have unexpected consequences. It is planned
to implement a mechanism to preserve auto-generated subnet ids in a
future version of Kea. However, the only remedy for this issue
at present is to
manually specify a unique identifier for each subnet.
</p><p>
The following configuration will assign the specified subnet
identifier to the newly configured subnet:
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
<strong class="userinput"><code>"id": 1024</code></strong>,
...
}
]
}
</pre><p>
This identifier will not change for this subnet unless the "id" parameter is
removed or set to 0. The value of 0 forces auto-generation of the subnet
identifier.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-address-config"></a>7.2.7. Configuration of IPv4 Address Pools</h3></div></div></div><p>
The essential role of DHCPv4 server is address assignment. The server has to
be configured with at least one subnet and one pool of dynamic addresses to
be managed. For example, assume that the server is connected to a network
segment that uses the 192.0.2.0/24 prefix. The Administrator of that network
has decided that addresses from range 192.0.2.10 to 192.0.2.20 are going to
be managed by the Dhcp4 server. Such a configuration can be achieved in the
following way:
</p><pre class="screen">
"Dhcp4": {
<strong class="userinput"><code>"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{ "pool": "192.0.2.10 - 192.0.2.20" }
],
...
}
]</code></strong>
}</pre><p>
Note that subnet is defined as a simple string, but the <span class="command"><strong>pools</strong></span> parameter is
actually a list of pools: for this reason, the pools definition is enclosed
in square brackets, even though only one range of addresses is
specified in this example.</p><p>Each pool is a structure that contains the parameters
that describe a single pool. Currently there is only one parameter,
<span class="command"><strong>pool</strong></span>, which gives the range of addresses
in the pool. Additional parameters will be added in future
releases of Kea.</p><p>It is possible to define more than one pool in a subnet: continuing
the previous example, further assume that 192.0.2.64/26 should be also be
managed by the server. It could be written as 192.0.2.64 to
192.0.2.127. Alternatively, it can be expressed more simply as
192.0.2.64/26. Both formats are supported by Dhcp4 and can be mixed in the
pool list. For example, one could define the following pools:
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
<strong class="userinput"><code>"pools": [
{ "pool": "192.0.2.10-192.0.2.20" },
{ "pool": "192.0.2.64/26" }
]</code></strong>,
...
}
],
...
}
</pre><p>
The number of pools is not limited, but for performance reasons it is recommended to
use as few as possible. White space in pool definitions is ignored, so
spaces before and after the hyphen are optional. They can be used to improve readability.
</p><p>
The server may be configured to serve more than one subnet:
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
...
},
{
"subnet": "192.0.3.0/24",
"pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
...
},
{
"subnet": "192.0.4.0/24",
"pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
...
}
]
}
</pre><p>
</p><p>
When configuring a DHCPv4 server using prefix/length notation, please pay
attention to the boundary values. When specifying that the server can use
a given pool, it will also be able to allocate the first (typically network
address) and the last (typically broadcast address) address from that pool.
In the aforementioned example of pool 192.0.3.0/24, both 192.0.3.0 and
192.0.3.255 addresses may be assigned as well. This may be invalid in some
network configurations. If you want to avoid this, please use the "min-max" notation.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-std-options"></a>7.2.8. Standard DHCPv4 options</h3></div></div></div><p>
One of the major features of the DHCPv4 server is to provide configuration
options to clients. Most of the options are sent by the server, only if the
client explicitly requests them using the Parameter Request List option.
Those that do not require being requested using the Parameter Request List
option are commonly used options, e.g. "Domain Server", and options which
require special behavior, e.g. "Client FQDN" is returned to the client
if the client has included this option in its message to the server.
</p><p>
The <a class="xref" href="#dhcp4-std-options-list" title="Table 7.1. List of standard DHCPv4 options">Table 7.1, “List of standard DHCPv4 options”</a> comprises the list of the
standard DHCPv4 options, whose values can be configured using the
configuration structures described in this section. This table excludes
the options which require special processing and thus cannot be configured
with some fixed values. The last column of this table specifies which
options can be sent by the server even when they are not requested in
the Parameter Request list option, and which are sent only when
explicitly requested. These options are marked with the values
'true' and 'false' respectively.
</p><p>
The following example shows how to configure the addresses of DNS
servers, which is one of the most frequently used options. Options
specified in this way are considered global and apply to all
configured subnets.
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"</code></strong>
},
...
]
}
</pre><p>
</p><p>
The <span class="command"><strong>name</strong></span> parameter specifies the
option name. For a list of currently supported names, see
<a class="xref" href="#dhcp4-std-options-list" title="Table 7.1. List of standard DHCPv4 options">Table 7.1, “List of standard DHCPv4 options”</a> below.
The <span class="command"><strong>code</strong></span> parameter specifies the option code, which must match one of the
values from that list. The next line specifies the option space, which must always
be set to "dhcp4" as these are standard DHCPv4 options. For
other option spaces, including custom option spaces, see <a class="xref" href="#dhcp4-option-spaces" title="7.2.11. Nested DHCPv4 Options (Custom Option Spaces)">Section 7.2.11, “Nested DHCPv4 Options (Custom Option Spaces)”</a>. The next line specifies the format in
which the data will be entered: use of CSV (comma
separated values) is recommended. The sixth line gives the actual value to
be sent to clients. Data is specified as normal text, with
values separated by commas if more than one value is
allowed.
</p><p>
Options can also be configured as hexadecimal values. If
<span class="command"><strong>csv-format</strong></span> is
set to false, option data must be specified as a hexadecimal string. The
following commands configure the domain-name-servers option for all
subnets with the following addresses: 192.0.3.1 and 192.0.3.2.
Note that <span class="command"><strong>csv-format</strong></span> is set to false.
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": false,
"data": "C0 00 03 01 C0 00 03 02"</code></strong>
},
...
],
...
}</pre><p>
</p><p>
Most of the parameters in the "option-data" structure are optional and
can be omitted in some circumstances as discussed in the
<a class="xref" href="#dhcp4-option-data-defaults" title="7.2.12. Unspecified parameters for DHCPv4 option configuration">Section 7.2.12, “Unspecified parameters for DHCPv4 option configuration”</a>.
</p><p>
It is possible to specify or override options on a per-subnet basis. If
clients connected to most of your subnets are expected to get the
same values of a given option, you should use global options: you
can then override specific values for a small number of subnets.
On the other hand, if you use different values in each subnet,
it does not make sense to specify global option values
(Dhcp4/option-data), rather you should set only subnet-specific values
(Dhcp4/subnet[X]/option-data[Y]).
</p><p>
The following commands override the global
DNS servers option for a particular subnet, setting a single DNS
server with address 192.0.2.3.
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
<strong class="userinput"><code>"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.3"
},
...
]</code></strong>,
...
},
...
],
...
}
</pre><p>
</p><p>
The currently supported standard DHCPv4 options are
listed in <a class="xref" href="#dhcp4-std-options-list" title="Table 7.1. List of standard DHCPv4 options">Table 7.1, “List of standard DHCPv4 options”</a>
and <a class="xref" href="#dhcp4-std-options-list-part2" title="Table 7.2. List of standard DHCPv4 options (continued)">Table 7.2, “List of standard DHCPv4 options (continued)”</a>.
The "Name" and "Code"
are the values that should be used as a name in the option-data
structures. "Type" designates the format of the data: the meanings of
the various types is given in <a class="xref" href="#dhcp-types" title="Table 7.3. List of standard DHCP option types">Table 7.3, “List of standard DHCP option types”</a>.
</p><p>
Some options are designated as arrays, which means that more than one
value is allowed in such an option. For example the option time-servers
allows the specification of more than one IPv4 address, so allowing
clients to obtain the addresses of multiple NTP servers.
</p><p>
The <a class="xref" href="#dhcp4-custom-options" title="7.2.9. Custom DHCPv4 options">Section 7.2.9, “Custom DHCPv4 options”</a> describes the configuration
syntax to create custom option definitions (formats). It is generally not
allowed to create custom definitions for standard options, even if the
definition being created matches the actual option format defined in the
RFCs. There is an exception from this rule for standard options for which
Kea does not provide a definition yet. In order to use such options,
a server administrator must create a definition as described in
<a class="xref" href="#dhcp4-custom-options" title="7.2.9. Custom DHCPv4 options">Section 7.2.9, “Custom DHCPv4 options”</a> in the 'dhcp4' option space. This
definition should match the option format described in the relevant
RFC but the configuration mechanism will allow any option format as it has
no means to validate the format at the moment.
</p><p>
</p><div class="table"><a name="dhcp4-std-options-list"></a><p class="title"><b>Table 7.1. List of standard DHCPv4 options</b></p><div class="table-contents"><table summary="List of standard DHCPv4 options" border="1"><colgroup><col class="name"><col align="center" class="code"><col align="center" class="type"><col align="center" class="array"><col align="center" class="always-returned"></colgroup><thead><tr><th>Name</th><th align="center">Code</th><th align="center">Type</th><th align="center">Array?</th><th align="center">Returned if not requested?</th></tr></thead><tbody><tr><td>time-offset</td><td align="center">2</td><td align="center">int32</td><td align="center">false</td><td align="center">false</td></tr><tr><td>routers</td><td align="center">3</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">true</td></tr><tr><td>time-servers</td><td align="center">4</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>name-servers</td><td align="center">5</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>domain-name-servers</td><td align="center">6</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">true</td></tr><tr><td>log-servers</td><td align="center">7</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>cookie-servers</td><td align="center">8</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>lpr-servers</td><td align="center">9</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>impress-servers</td><td align="center">10</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>resource-location-servers</td><td align="center">11</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>boot-size</td><td align="center">13</td><td align="center">uint16</td><td align="center">false</td><td align="center">false</td></tr><tr><td>merit-dump</td><td align="center">14</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>domain-name</td><td align="center">15</td><td align="center">fqdn</td><td align="center">false</td><td align="center">true</td></tr><tr><td>swap-server</td><td align="center">16</td><td align="center">ipv4-address</td><td align="center">false</td><td align="center">false</td></tr><tr><td>root-path</td><td align="center">17</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>extensions-path</td><td align="center">18</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>ip-forwarding</td><td align="center">19</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>non-local-source-routing</td><td align="center">20</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>policy-filter</td><td align="center">21</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>max-dgram-reassembly</td><td align="center">22</td><td align="center">uint16</td><td align="center">false</td><td align="center">false</td></tr><tr><td>default-ip-ttl</td><td align="center">23</td><td align="center">uint8</td><td align="center">false</td><td align="center">false</td></tr><tr><td>path-mtu-aging-timeout</td><td align="center">24</td><td align="center">uint32</td><td align="center">false</td><td align="center">false</td></tr><tr><td>path-mtu-plateau-table</td><td align="center">25</td><td align="center">uint16</td><td align="center">true</td><td align="center">false</td></tr><tr><td>interface-mtu</td><td align="center">26</td><td align="center">uint16</td><td align="center">false</td><td align="center">false</td></tr><tr><td>all-subnets-local</td><td align="center">27</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>broadcast-address</td><td align="center">28</td><td align="center">ipv4-address</td><td align="center">false</td><td align="center">false</td></tr><tr><td>perform-mask-discovery</td><td align="center">29</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>mask-supplier</td><td align="center">30</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>router-discovery</td><td align="center">31</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>router-solicitation-address</td><td align="center">32</td><td align="center">ipv4-address</td><td align="center">false</td><td align="center">false</td></tr><tr><td>static-routes</td><td align="center">33</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>trailer-encapsulation</td><td align="center">34</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>arp-cache-timeout</td><td align="center">35</td><td align="center">uint32</td><td align="center">false</td><td align="center">false</td></tr><tr><td>ieee802-3-encapsulation</td><td align="center">36</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr><tr><td>default-tcp-ttl</td><td align="center">37</td><td align="center">uint8</td><td align="center">false</td><td align="center">false</td></tr><tr><td>tcp-keepalive-interval</td><td align="center">38</td><td align="center">uint32</td><td align="center">false</td><td align="center">false</td></tr><tr><td>tcp-keepalive-garbage</td><td align="center">39</td><td align="center">boolean</td><td align="center">false</td><td align="center">false</td></tr></tbody></table></div></div><p><br class="table-break">
</p><p>
</p><div class="table"><a name="dhcp4-std-options-list-part2"></a><p class="title"><b>Table 7.2. List of standard DHCPv4 options (continued)</b></p><div class="table-contents"><table summary="List of standard DHCPv4 options (continued)" border="1"><colgroup><col class="name"><col align="center" class="code"><col align="center" class="type"><col align="center" class="array"><col align="center" class="always-returned"></colgroup><thead><tr><th>Name</th><th align="center">Code</th><th align="center">Type</th><th align="center">Array?</th><th align="center">Returned if not requested?</th></tr></thead><tbody><tr><td>nis-domain</td><td align="center">40</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>nis-servers</td><td align="center">41</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>ntp-servers</td><td align="center">42</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>vendor-encapsulated-options</td><td align="center">43</td><td align="center">empty</td><td align="center">false</td><td align="center">false</td></tr><tr><td>netbios-name-servers</td><td align="center">44</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>netbios-dd-server</td><td align="center">45</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>netbios-node-type</td><td align="center">46</td><td align="center">uint8</td><td align="center">false</td><td align="center">false</td></tr><tr><td>netbios-scope</td><td align="center">47</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>font-servers</td><td align="center">48</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>x-display-manager</td><td align="center">49</td><td align="center">ipv4-address</td><td align="center">true</td><td align="center">false</td></tr><tr><td>dhcp-option-overload</td><td align="center">52</td><td align="center">uint8</td><td align="center">false</td><td align="center">false</td></tr><tr><td>dhcp-message</td><td align="center">56</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>dhcp-max-message-size</td><td align="center">57</td><td align="center">uint16</td><td align="center">false</td><td align="center">false</td></tr><tr><td>vendor-class-identifier</td><td align="center">60</td><td align="center">binary</td><td align="center">false</td><td align="center">false</td></tr><tr><td>nwip-domain-name</td><td align="center">62</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>nwip-suboptions</td><td align="center">63</td><td align="center">binary</td><td align="center">false</td><td align="center">false</td></tr><tr><td>tftp-server-name</td><td align="center">66</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>boot-file-name</td><td align="center">67</td><td align="center">string</td><td align="center">false</td><td align="center">false</td></tr><tr><td>user-class</td><td align="center">77</td><td align="center">binary</td><td align="center">false</td><td align="center">false</td></tr><tr><td>client-system</td><td align="center">93</td><td align="center">uint16</td><td align="center">true</td><td align="center">false</td></tr><tr><td>client-ndi</td><td align="center">94</td><td align="center">record (uint8, uint8, uint8)</td><td align="center">false</td><td align="center">false</td></tr><tr><td>uuid-guid</td><td align="center">97</td><td align="center">record (uint8, binary)</td><td align="center">false</td><td align="center">false</td></tr><tr><td>subnet-selection</td><td align="center">118</td><td align="center">ipv4-address</td><td align="center">false</td><td align="center">false</td></tr><tr><td>domain-search</td><td align="center">119</td><td align="center">binary</td><td align="center">false</td><td align="center">false</td></tr><tr><td>vivco-suboptions</td><td align="center">124</td><td align="center">binary</td><td align="center">false</td><td align="center">false</td></tr><tr><td>vivso-suboptions</td><td align="center">125</td><td align="center">binary</td><td align="center">false</td><td align="center">false</td></tr></tbody></table></div></div><p><br class="table-break">
</p><p>
</p><div class="table"><a name="dhcp-types"></a><p class="title"><b>Table 7.3. List of standard DHCP option types</b></p><div class="table-contents"><table summary="List of standard DHCP option types" border="1"><colgroup><col class="name"><col class="meaning"></colgroup><thead><tr><th>Name</th><th>Meaning</th></tr></thead><tbody><tr><td>binary</td><td>An arbitrary string of bytes, specified as a set of hexadecimal digits.</td></tr><tr><td>boolean</td><td>Boolean value with allowed values true or false</td></tr><tr><td>empty</td><td>No value, data is carried in suboptions</td></tr><tr><td>fqdn</td><td>Fully qualified domain name (e.g. www.example.com)</td></tr><tr><td>ipv4-address</td><td>IPv4 address in the usual dotted-decimal notation (e.g. 192.0.2.1)</td></tr><tr><td>ipv6-address</td><td>IPv6 address in the usual colon notation (e.g. 2001:db8::1)</td></tr><tr><td>record</td><td>Structured data that may comprise any types (except "record" and "empty")</td></tr><tr><td>string</td><td>Any text</td></tr><tr><td>uint8</td><td>8 bit unsigned integer with allowed values 0 to 255</td></tr><tr><td>uint16</td><td>16 bit unsigned integer with allowed values 0 to 65535</td></tr><tr><td>uint32</td><td>32 bit unsigned integer with allowed values 0 to 4294967295</td></tr></tbody></table></div></div><p><br class="table-break">
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-custom-options"></a>7.2.9. Custom DHCPv4 options</h3></div></div></div><p>Kea supports custom (non-standard) DHCPv4 options. Assume
that we want to define a new DHCPv4 option called "foo" which
will have code 222 and will convey a single unsigned 32 bit
integer value. We can define such an option by using the
following entry in the configuration file:
</p><pre class="screen">
"Dhcp4": {
"option-def": [
{
<strong class="userinput"><code>"name": "foo",
"code": 222,
"type": "uint32",
"array": false,
"record-types": "",
"space": "dhcp4",
"encapsulate": ""</code></strong>
}, ...
],
...
}
</pre><p>
The <span class="command"><strong>false</strong></span> value of the <span class="command"><strong>array</strong></span>
parameter determines that the option does NOT comprise an array of
"uint32" values but rather a single value. Two other parameters have been
left blank: <span class="command"><strong>record-types</strong></span> and
<span class="command"><strong>encapsulate</strong></span>. The former specifies the comma separated
list of option data fields if the option comprises a record of data
fields. This should be non-empty if the <span class="command"><strong>type</strong></span> is set to
"record". Otherwise it must be left blank. The latter parameter specifies
the name of the option space being encapsulated by the particular
option. If the particular option does not encapsulate any option space it
should be left blank. Note that the above set of comments define the
format of the new option and do not set its values.
</p><p>The <span class="command"><strong>name</strong></span>, <span class="command"><strong>code</strong></span> and
<span class="command"><strong>type</strong></span> parameters are required, all others are
optional. The <span class="command"><strong>array</strong></span> default value is
<span class="command"><strong>false</strong></span>. The <span class="command"><strong>record-types</strong></span>
and <span class="command"><strong>encapsulate</strong></span> default values are blank
(i.e. ""). The default <span class="command"><strong>space</strong></span> is "dhcp4".
</p><p>Once the new option format is defined, its value is set
in the same way as for a standard option. For example the following
commands set a global value that applies to all subnets.
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "foo",
"code": 222,
"space": "dhcp4",
"csv-format": true,
"data": "12345"</code></strong>
}, ...
],
...
}
</pre><p>
</p><p>New options can take more complex forms than simple use of
primitives (uint8, string, ipv4-address etc): it is possible to
define an option comprising a number of existing primitives.
Assume we want to define a new option that will consist of
an IPv4 address, followed by an unsigned 16 bit integer, followed by
a boolean value, followed by a text string. Such an option could
be defined in the following way:
</p><pre class="screen">
"Dhcp4": {
"option-def": [
{
<strong class="userinput"><code>"name": "bar",
"code": 223,
"space": "dhcp4",
"type": "record",
"array": false,
"record-types": "ipv4-address, uint16, boolean, string",
"encapsulate": ""</code></strong>
}, ...
],
...
}
</pre><p>
The <span class="command"><strong>type</strong></span> is set to "record" to indicate that the option contains
multiple values of different types. These types are given as a comma-separated
list in the <span class="command"><strong>record-types</strong></span> field and should be those listed in <a class="xref" href="#dhcp-types" title="Table 7.3. List of standard DHCP option types">Table 7.3, “List of standard DHCP option types”</a>.
</p><p>
The values of the option are set as follows:
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "bar",
"space": "dhcp4",
"code": 223,
"csv-format": true,
"data": "192.0.2.100, 123, true, Hello World"</code></strong>
}
],
...
}</pre><p>
<span class="command"><strong>csv-format</strong></span> is set to <span class="command"><strong>true</strong></span> to indicate
that the <span class="command"><strong>data</strong></span> field comprises a command-separated list
of values. The values in the <span class="command"><strong>data</strong></span> must correspond to
the types set in the <span class="command"><strong>record-types</strong></span> field of the option
definition.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>In the general case, boolean values are specified as <span class="command"><strong>true</strong></span> or
<span class="command"><strong>false</strong></span>, without quotes. Some specific boolean parameters may
accept also <span class="command"><strong>"true"</strong></span>, <span class="command"><strong>"false"</strong></span>,
<span class="command"><strong>0</strong></span>, <span class="command"><strong>1</strong></span>, <span class="command"><strong>"0"</strong></span> and
<span class="command"><strong>"1"</strong></span>. Future Kea versions will accept all those values
for all boolean parameters.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-vendor-opts"></a>7.2.10. DHCPv4 Vendor Specific Options</h3></div></div></div><p>
Currently there are two option spaces defined for the DHCPv4 daemon:
"dhcp4" (for the top level DHCPv4 options) and
"vendor-encapsulated-options-space", which is empty by default but
options can be defined in it. Those options will be carried in the
Vendor Specific Information option (code 43). The following examples
show how to define an option "foo", with code 1, that consists of an
IPv4 address, an unsigned 16 bit integer and a string. The "foo"
option is conveyed in a Vendor Specific Information option.
</p><p>
The first step is to define the format of the option:
</p><pre class="screen">
"Dhcp4": {
"option-def": [
{
<strong class="userinput"><code>"name": "foo",
"code": 1,
"space": "vendor-encapsulated-options-space",
"type": "record",
"array": false,
"record-types": "ipv4-address, uint16, string",
"encapsulate": ""</code></strong>
}
],
...
}</pre><p>
(Note that the option space is set to "vendor-encapsulated-options-space".)
Once the option format is defined, the next step is to define actual values
for that option:
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "foo",
"space": "vendor-encapsulated-options-space",
"code": 1,
"csv-format": true,
"data": "192.0.2.3, 123, Hello World"</code></strong>
}
],
...
}</pre><p>
We also include the Vendor Specific Information option, the option
that conveys our sub-option "foo". This is required, else the option
will not be included in messages sent to the client.
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "vendor-encapsulated-options"</code></strong>
}
],
...
}</pre><p>
Alternatively, the option can be specified using its code.
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"code": 43</code></strong>
}
],
...
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-option-spaces"></a>7.2.11. Nested DHCPv4 Options (Custom Option Spaces)</h3></div></div></div><p>It is sometimes useful to define completely new option
space. This is the case when user creates new option in the
standard option space ("dhcp4") and wants this option
to convey sub-options. Since they are in a separate space,
sub-option codes will have a separate numbering scheme and may
overlap with the codes of standard options.
</p><p>Note that creation of a new option space when defining
sub-options for a standard option is not required, because it is
created by default if the standard option is meant to convey any
sub-options (see <a class="xref" href="#dhcp4-vendor-opts" title="7.2.10. DHCPv4 Vendor Specific Options">Section 7.2.10, “DHCPv4 Vendor Specific Options”</a>).
</p><p>
Assume that we want to have a DHCPv4 option called "container" with
code 222 that conveys two sub-options with codes 1 and 2.
First we need to define the new sub-options:
</p><pre class="screen">
"Dhcp4": {
"option-def": [
{
<strong class="userinput"><code>"name": "subopt1",
"code": 1,
"space": "isc",
"type": "ipv4-address",
"record-types": "",
"array": false,
"encapsulate ""
},
{
"name": "subopt2",
"code": 2,
"space": "isc",
"type": "string",
"record-types": "",
"array": false,
"encapsulate": ""</code></strong>
}
],
...
}</pre><p>
Note that we have defined the options to belong to a new option space
(in this case, "isc").
</p><p>
The next step is to define a regular DHCPv4 option with our desired
code and specify that it should include options from the new option space:
</p><pre class="screen">
"Dhcp4": {
"option-def": [
...,
{
<strong class="userinput"><code>"name": "container",
"code": 222,
"space": "dhcp4",
"type": "empty",
"array": false,
"record-types": "",
"encapsulate": "isc"</code></strong>
}
],
...
}</pre><p>
The name of the option space in which the sub-options are defined
is set in the "encapsulate" field. The "type" field is set to "empty"
to indicate that this option does not carry any data other than
sub-options.
</p><p>
Finally, we can set values for the new options:
</p><pre class="screen">
"Dhcp4": {
"option-data": [
{
<strong class="userinput"><code>"name": "subopt1",
"code": 1,
"space": "isc",
"data": "192.0.2.3"</code></strong>
},
}
<strong class="userinput"><code>"name": "subopt2",
"code": 2,
"space": "isc",
"data": "Hello world"</code></strong>
},
{
<strong class="userinput"><code>"name": "container",
"code": 222,
"space": "dhcp4"</code></strong>
}
],
...
}
</pre><p>
</p><p>Note that it is possible to create an option which carries some data
in addition to the sub-options defined in the encapsulated option space. For example,
if the "container" option from the previous example was required to carry an uint16
value as well as the sub-options, the "type" value would have to be set to "uint16" in
the option definition. (Such an option would then have the following
data structure: DHCP header, uint16 value, sub-options.) The value specified
with the "data" parameter — which should be a valid integer enclosed in quotes,
e.g. "123" — would then be assigned to the uint16 field in the "container" option.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-option-data-defaults"></a>7.2.12. Unspecified parameters for DHCPv4 option configuration</h3></div></div></div><p>In many cases it is not required to specify all parameters for
an option configuration and the default values may be used. However, it is
important to understand the implications of not specifying some of them
as it may result in configuration errors. The list below explains
the behavior of the server when a particular parameter is not explicitly
specified:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>name</strong></span> - the server requires an option name or
option code to identify an option. If this parameter is unspecified, the
option code must be specified.
</li><li class="listitem"><span class="command"><strong>code</strong></span> - the server requires an option name or
option code to identify an option. This parameter may be left unspecified if
the <span class="command"><strong>name</strong></span> parameter is specified. However, this also
requires that the particular option has its definition (it is either a
standard option or an administrator created a definition for the option
using an 'option-def' structure), as the option definition associates an
option with a particular name. It is possible to configure an option
for which there is no definition (unspecified option format).
Configuration of such options requires the use of option code.
</li><li class="listitem"><span class="command"><strong>space</strong></span> - if the option space is unspecified it
will default to 'dhcp4' which is an option space holding DHCPv4 standard
options.
</li><li class="listitem"><span class="command"><strong>data</strong></span> - if the option data is unspecified it
defaults to an empty value. The empty value is mostly used for the
options which have no payload (boolean options), but it is legal to specify
empty values for some options which carry variable length data and which
spec allows for the length of 0. For such options, the data parameter
may be omitted in the configuration.</li><li class="listitem"><span class="command"><strong>csv-format</strong></span> - if this value is not specified
and the definition for the particular option exists, the server will assume
that the option data is specified as a list of comma separated values to be
assigned to individual fields of the DHCP option. If the definition
does not exist for this option, the server will assume that the data
parameter contains the option payload in the binary format (represented
as a string of hexadecimal digits). Note that not specifying this
parameter doesn't imply that it defaults to a fixed value, but
the configuration data interpretation also depends on the presence
of the option definition. An administrator must be aware if the
definition for the particular option exists when this parameter
is not specified. It is generally recommended to not specify this
parameter only for the options for which the definition exists, e.g.
standard options. Setting <span class="command"><strong>csv-format</strong></span> to an explicit
value will cause the server to strictly check the format of the option
data specified.
</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-stateless-configuration"></a>7.2.13. Stateless Configuration of DHCPv4 clients</h3></div></div></div><p>The DHCPv4 server supports the stateless client configuration whereby the
client has an IP address configured (e.g. using manual configuration) and only
contacts the server to obtain other configuration parameters, e.g. DNS servers' addresses.
In order to obtain the stateless configuration parameters the client sends the
DHCPINFORM message to the server with the "ciaddr" set to the address that the
client is currently using. The server unicasts the DHCPACK message to the
client that includes the stateless configuration ("yiaddr" not set).
</p><p>The server will respond to the DHCPINFORM when the client is associated
with the particular subnet defined in the server's configuration. The example
subnet configuration will look like this:
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24"
"option-data": [ {
"name": "domain-name-servers",
"code": 6,
"data": "192.0.2.200,192.0.2.201",
"csv-format": true,
"space": "dhcp4"
} ]
}
]
}</pre><p>
</p><p>This subnet specifies the single option which will be included in
the DHCPACK message to the client in response to DHCPINFORM. Note that
the subnet definition does not require the address pool configuration
if it will be used solely for the stateless configuration.
</p><p>This server will associate the subnet with the client if one of
the following conditions is met:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">The DHCPINFORM is relayed and the giaddr matches the
configured subnet.</li><li class="listitem">The DHCPINFORM is unicast from the client and the ciaddr
matches the configured subnet.</li><li class="listitem">The DHCPINFORM is unicast from the client, the ciaddr is
not set but the source address of the IP packet matches the
configured subnet.</li><li class="listitem">The DHCPINFORM is not relayed and the IP address on the
interface on which the message is received matches the configured
subnet.</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-client-classifier"></a>7.2.14. Client Classification in DHCPv4</h3></div></div></div><p>
The DHCPv4 server includes support for client classification. At the
current time the capabilities of the classification process are limited
but it is expected they will be expanded in the future. For a deeper
discussion of the classification process see <a class="xref" href="#classify" title="Chapter 12. Client Classification">Chapter 12, <i>Client Classification</i></a>.
</p><p>
In certain cases it is useful to differentiate between different types of
clients and treat them accordingly. It is envisaged that client
classification will be used for changing the behavior of almost any part of
the DHCP message processing, including the assignment of leases from different
pools, the assignment of different options (or different values of the same
options) etc. In the current release of the software however, there are
only three mechanisms that take advantage of client classification:
subnet selection, assignment of different options, and, for cable modems, there
are specific options for use with the TFTP server address and the boot file field.
</p><p>
Kea can be instructed to limit access to given subnets based on class information.
This is particularly useful for cases where two types of devices share the
same link and are expected to be served from two different subnets. The
primary use case for such a scenario is cable networks. There are two
classes of devices: the cable modem itself, which should be handed a lease
from subnet A and all other devices behind the modem that should get a lease
from subnet B. That segregation is essential to prevent overly curious
users from playing with their cable modems. For details on how to set up
class restrictions on subnets, see <a class="xref" href="#classification-subnets" title="12.5. Configuring Subnets With Class Information">Section 12.5, “Configuring Subnets With Class Information”</a>.
</p><p>
The process of doing classification is conducted in three steps. The first step
is to assess an incoming packet and assign it to zero or more classes. The
second step is to choose a subnet, possibly based on the class information.
The third step is to assign options again possibly based on the class
information.
</p><p>
There are two methods of doing classification. The first is automatic and relies
on examining the values in the vendor class options. Information from these
options is extracted and a class name is constructed from it and added to
the class list for the packet. The second allows you to specify an expression
that is evaluated for each packet. If the result is true the packet is
a member of the class.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Care should be taken with client classification as it is easy for
clients that do not meet class criteria to be denied any service altogether.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp55897344"></a>7.2.14.1. Using Vendor Class Information in Classification</h4></div></div></div><p>
The server checks whether an incoming packet includes the vendor class identifier
option (60). If it does, the content of that option is prepended with
"VENDOR_CLASS_" then it is interpreted as a class. For example,
modern cable modems will send this option with value "docsis3.0"
and as a result the packet will belong to class "VENDOR_CLASS_docsis3.0".
</p><p>
For clients that belong to the VENDOR_CLASS_docsis3.0 class, the siaddr
field is set to the value of next-server (if specified in a subnet). If
there is a boot-file-name option specified, its value is also set in the
file field in the DHCPv4 packet. For eRouter1.0 class, the siaddr is
always set to 0.0.0.0. That capability is expected to be moved to
an external hook library that will be dedicated to cable modems.
</p><p>
This example shows a configuration using an automatically generated
"VENDOR_CLASS_" class. The Administrator of the network has
decided that addresses from range 192.0.2.10 to 192.0.2.20 are
going to be managed by the Dhcp4 server and only clients belonging to the
docsis3.0 client class are allowed to use that pool.
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
<strong class="userinput"><code>"client-class": "VENDOR_CLASS_docsis3.0"</code></strong>
}
],
...
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp55901984"></a>7.2.14.2. Defining and Using Custom Classes</h4></div></div></div><p>
The following example shows how to configure a class using an expression
and a subnet making use of that class. This configuration defines the
class named "Client_foo".
It is comprised of all clients who's client ids (option 61) start with the
string "foo". Members of this class will be given addresses from
192.0.2.10 to 192.0.2.20 and 192.0.2.1 and 192.0.2.2 as their domain name
servers. For a deeper discussion of the classification process see
<a class="xref" href="#classify" title="Chapter 12. Client Classification">Chapter 12, <i>Client Classification</i></a>.
</p><pre class="screen">
"Dhcp4": {
"client-classes": [
{<strong class="userinput"><code>
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]</code></strong>
},
...
],
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
<strong class="userinput"><code>"client-class": "Client_foo"</code></strong>
},
...
],
...
}</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-ddns-config"></a>7.2.15. Configuring DHCPv4 for DDNS</h3></div></div></div><p>
As mentioned earlier, kea-dhcp4 can be configured to generate requests to the
DHCP-DDNS server (referred to here as "D2" ) to update DNS entries. These requests are known as
NameChangeRequests or NCRs. Each NCR contains the following information:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Whether it is a request to add (update) or remove DNS entries
</p></li><li class="listitem"><p>
Whether the change requests forward DNS updates (A records), reverse
DNS updates (PTR records), or both.
</p></li><li class="listitem"><p>
The FQDN, lease address, and DHCID
</p></li></ol></div><p>
The parameters for controlling the generation of NCRs for submission to D2
are contained in the <span class="command"><strong>dhcp-ddns</strong></span> section of the kea-dhcp4 server
configuration. The mandatory parameters for the DHCP DDNS configuration
are <span class="command"><strong>enable-updates</strong></span> which is unconditionally
required, and <span class="command"><strong>qualifying-suffix</strong></span> which has no
default value and is required when <span class="command"><strong>enable-updates</strong></span>
is set to <span class="command"><strong>true</strong></span>.
The two (disabled and enabled) minimal DHCP DDNS configurations are:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"enable-updates": false</code></strong>
},
...
}
</pre><p>
and for example:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"enable-updates": true,
"qualifying-suffix": "example."</code></strong>
},
...
}
</pre><p>
The default values for the "dhcp-ddns" section are as follows:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>"server-ip": "127.0.0.1"</strong></span>
</li><li class="listitem">
<span class="command"><strong>"server-port": 53001</strong></span>
</li><li class="listitem">
<span class="command"><strong>"sender-ip": ""</strong></span>
</li><li class="listitem">
<span class="command"><strong>"sender-port": 0</strong></span>
</li><li class="listitem">
<span class="command"><strong>"max-queue-size": 1024</strong></span>
</li><li class="listitem">
<span class="command"><strong>"ncr-protocol": "UDP"</strong></span>
</li><li class="listitem">
<span class="command"><strong>"ncr-format": "JSON"</strong></span>
</li><li class="listitem">
<span class="command"><strong>"override-no-update": false</strong></span>
</li><li class="listitem">
<span class="command"><strong>"override-client-update": false</strong></span>
</li><li class="listitem">
<span class="command"><strong>"replace-client-name": false</strong></span>
</li><li class="listitem">
<span class="command"><strong>"generated-prefix": "myhost"</strong></span>
</li></ul></div><p>
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dhcpv4-d2-io-config"></a>7.2.15.1. DHCP-DDNS Server Connectivity</h4></div></div></div><p>
In order for NCRs to reach the D2 server, kea-dhcp4 must be able
to communicate with it. kea-dhcp4 uses the following configuration
parameters to control how it communications with D2:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>enable-updates</strong></span> - determines whether or not kea-dhcp4 will
generate NCRs. By default, this value is false hence DDNS updates are
disabled. To enable DDNS updates set this value to true:
</li><li class="listitem">
<span class="command"><strong>server-ip</strong></span> - IP address on which D2 listens for requests. The default is
the local loopback interface at address 127.0.0.1. You may specify
either an IPv4 or IPv6 address.
</li><li class="listitem">
<span class="command"><strong>server-port</strong></span> - port on which D2 listens for requests. The default value
is 53001.
</li><li class="listitem">
<span class="command"><strong>sender-ip</strong></span> - IP address which kea-dhcp4 should use to send requests to D2.
The default value is blank which instructs kea-dhcp4 to select a suitable
address.
</li><li class="listitem">
<span class="command"><strong>sender-port</strong></span> - port which kea-dhcp4 should use to send requests to D2. The
default value of 0 instructs kea-dhcp4 to select a suitable port.
</li><li class="listitem">
<span class="command"><strong>max-queue-size</strong></span> - maximum number of requests allowed to queue waiting to
be sent to D2. This value guards against requests accumulating
uncontrollably if they are being generated faster than they can be
delivered. If the number of requests queued for transmission reaches
this value, DDNS updating will be turned off until the queue backlog has
been sufficiently reduced. The intention is to allow the kea-dhcp4 server to
continue lease operations without running the risk that its memory usage
grows without limit. The default value is 1024.
</li><li class="listitem">
<span class="command"><strong>ncr-protocol</strong></span> - socket protocol use when sending requests to D2. Currently
only UDP is supported. TCP may be available in an upcoming release.
</li><li class="listitem">
<span class="command"><strong>ncr-format</strong></span> - packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be available
in future releases.
</li></ul></div><p>
By default, kea-dhcp-ddns is assumed to be running on the same machine as kea-dhcp4, and
all of the default values mentioned above should be sufficient.
If, however, D2 has been configured to listen on a different address or
port, these values must be altered accordingly. For example, if D2 has been
configured to listen on 192.168.1.10 port 900, the following configuration
would be required:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"server-ip": "192.168.1.10",
"server-port": 900</code></strong>,
...
},
...
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dhcpv4-d2-rules-config"></a>7.2.15.2. When Does the kea-dhcp4 Server Generate DDNS Requests?</h4></div></div></div><p>kea-dhcp4 follows the behavior prescribed for DHCP servers in
<a class="ulink" href="http://tools.ietf.org/html/rfc4702" target="_top">RFC 4702</a>.
It is important to keep in mind that kea-dhcp4 provides the initial decision
making of when and what to update and forwards that information to D2 in
the form of NCRs. Carrying out the actual DNS updates and dealing with
such things as conflict resolution are within the purview of D2 itself (<a class="xref" href="#dhcp-ddns-server" title="Chapter 10. The DHCP-DDNS Server">Chapter 10, <i>The DHCP-DDNS Server</i></a>).
This section describes when kea-dhcp4 will generate NCRs and the
configuration parameters that can be used to influence this decision.
It assumes that the "enable-updates" parameter is true.
</p><p>
In general, kea-dhcp4 will generate DDNS update requests when:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
A new lease is granted in response to a DHCP REQUEST
</p></li><li class="listitem"><p>
An existing lease is renewed but the FQDN associated with it has
changed.
</p></li><li class="listitem"><p>
An existing lease is released in response to a DHCP RELEASE
</p></li></ol></div><p>
In the second case, lease renewal, two DDNS requests will be issued: one
request to remove entries for the previous FQDN and a second request to
add entries for the new FQDN. In the last case, a lease release, a
single DDNS request to remove its entries will be made. The decision
making involved when granting a new lease (the first case) is more
involved and is discussed next.
</p><p>
When a new lease is granted, kea-dhcp4 will generate a DDNS
update request if the DHCP REQUEST contains either the FQDN option
(code 81) or the Host Name option (code 12). If both are present,
the server will use the FQDN option. By default kea-dhcp4
will respect the FQDN N and S flags specified by the client as shown
in the following table:
</p><div class="table"><a name="fqdn-flag-table"></a><p class="title"><b>Table 7.4. Default FQDN Flag Behavior</b></p><div class="table-contents"><table summary="Default FQDN Flag Behavior" border="1"><colgroup><col align="left" class="cflags"><col align="left" class="meaning"><col align="left" class="response"><col align="left" class="sflags"></colgroup><thead><tr><th align="left">Client Flags:N-S</th><th align="left">Client Intent</th><th align="left">Server Response</th><th align="left">Server Flags:N-S-O</th></tr></thead><tbody><tr><td align="left">0-0</td><td align="left">
Client wants to do forward updates, server should do reverse updates
</td><td align="left">Server generates reverse-only request</td><td align="left">1-0-0</td></tr><tr><td align="left">0-1</td><td align="left">Server should do both forward and reverse updates</td><td align="left">Server generates request to update both directions</td><td align="left">0-1-0</td></tr><tr><td align="left">1-0</td><td align="left">Client wants no updates done</td><td align="left">Server does not generate a request</td><td align="left">1-0-0</td></tr></tbody></table></div></div><br class="table-break"><p>
The first row in the table above represents "client delegation". Here
the DHCP client states that it intends to do the forward DNS updates and
the server should do the reverse updates. By default, kea-dhcp4 will honor
the client's wishes and generate a DDNS request to the DHCP-DDNS server to update only
reverse DNS data. The parameter <span class="command"><strong>override-client-update</strong></span> can be used
to instruct the server to override client delegation requests. When
this parameter is true, kea-dhcp4 will disregard requests for client
delegation and generate a DDNS request to update both forward and
reverse DNS data. In this case, the N-S-O flags in the server's
response to the client will be 0-1-1 respectively.
</p><p>
(Note that the flag combination N=1, S=1 is prohibited according to
<a class="ulink" href="http://tools.ietf.org/html/rfc4702" target="_top">RFC 4702</a>. If such a combination is received from the client, the packet
will be dropped by kea-dhcp4.)
</p><p>
To override client delegation, set the following values in your configuration
file:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"override-client-update": true</code></strong>,
...
},
...
}
</pre><p>
The third row in the table above describes the case in which the client
requests that no DNS updates be done. The parameter, <span class="command"><strong>override-no-update</strong></span>,
can be used to instruct the server to disregard the client's wishes. When
this parameter is true, kea-dhcp4 will generate a DDNS update request to kea-dhcp-ddns
even if the client requests that no updates be done. The N-S-O flags in the
server's response to the client will be 0-1-1.
</p><p>
To override client delegation, the following values should be set in your configuration:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"override-no-update": true</code></strong>,
...
},
...
}
</pre><p>
kea-dhcp4 will always generate DDNS update requests if the client request
only contains the Host Name option. In addition it will include an FQDN
option in the response to the client with the FQDN N-S-O flags set to
0-1-0 respectively. The domain name portion of the FQDN option will be
the name submitted to D2 in the DDNS update request.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dhcpv4-fqdn-name-generation"></a>7.2.15.3. kea-dhcp4 name generation for DDNS update requests</h4></div></div></div><p>Each NameChangeRequest must of course include the fully qualified domain
name whose DNS entries are to be affected. kea-dhcp4 can be configured to
supply a portion or all of that name based upon what it receives from
the client in the DHCP REQUEST.</p><p>
The rules for determining the FQDN option are as follows:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
If configured to do, so ignore the DHCPREQUEST contents and generate a
FQDN using a configurable prefix and suffix.
</p></li><li class="listitem"><p>
If the DHCPREQUEST contains the client FQDN option, the candidate
name is taken from there, otherwise it is taken from the Host Name option.
The candidate name may then be modified:
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>
If the candidate name is a fully qualified domain name, use it.
</p></li><li class="listitem"><p>
If the candidate name is a partial (i.e. unqualified) name then
add a configurable suffix to the name and use the result as the FQDN.
</p></li><li class="listitem"><p>
If the candidate name is a empty, generate a FQDN using a
configurable prefix and suffix.
</p></li></ol></div><p>
</p></li></ol></div><p>
To instruct kea-dhcp4 to always generate the FQDN for a client, set the
parameter <span class="command"><strong>replace-client-name</strong></span> to true as follows:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"replace-client-name": true</code></strong>,
...
},
...
}
</pre><p>
The prefix used in the generation of a FQDN is specified by the
<span class="command"><strong>generated-prefix</strong></span> parameter. The default value is "myhost". To alter
its value simply set it to the desired string:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"generated-prefix": "another.host"</code></strong>,
...
},
...
}
</pre><p>
The suffix used when generating a FQDN or when qualifying a
partial name is specified by
the <span class="command"><strong>qualifying-suffix</strong></span> parameter. This
parameter has no default value, thus it is mandatory when
DDNS updates are enabled.
To set its value simply set it to the desired string:
</p><pre class="screen">
"Dhcp4": {
"dhcp-ddns": {
<strong class="userinput"><code>"qualifying-suffix": "foo.example.org"</code></strong>,
...
},
...
}
</pre></div><p>
When generating a name, kea-dhcp4 will construct name of the format:
</p><p>
[generated-prefix]-[address-text].[qualifying-suffix].
</p><p>
where address-text is simply the lease IP address converted to a
hyphenated string. For example, if the lease address is 172.16.1.10,
the qualifying suffix "example.com", and the default value is used for
<span class="command"><strong>generated-prefix</strong></span>, the generated FQDN would be:
</p><p>
myhost-172-16-1-10.example.com.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-next-server"></a>7.2.16. Next Server (siaddr)</h3></div></div></div><p>In some cases, clients want to obtain configuration from the TFTP server.
Although there is a dedicated option for it, some devices may use the siaddr field
in the DHCPv4 packet for that purpose. That specific field can be configured
using <span class="command"><strong>next-server</strong></span> directive. It is possible to define it in the global scope or
for a given subnet only. If both are defined, the subnet value takes precedence.
The value in subnet can be set to 0.0.0.0, which means that <span class="command"><strong>next-server</strong></span> should
not be sent. It may also be set to an empty string, which means the same as if
it was not defined at all, i.e. use the global value.
</p><pre class="screen">
"Dhcp4": {
<strong class="userinput"><code>"next-server": "192.0.2.123"</code></strong>,
...,
"subnet4": [
{
<strong class="userinput"><code>"next-server": "192.0.2.234"</code></strong>,
...
}
]
}
</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-echo-client-id"></a>7.2.17. Echoing Client-ID (RFC 6842)</h3></div></div></div><p>The original DHCPv4 specification
(<a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>)
states that the DHCPv4
server must not send back client-id options when responding to
clients. However, in some cases that confused clients that did
not have MAC address or client-id; see
<a class="ulink" href="http://tools.ietf.org/html/rfc6842" target="_top">RFC 6842</a>.
for details. That
behavior has changed with the publication of
<a class="ulink" href="http://tools.ietf.org/html/rfc6842" target="_top">RFC 6842</a>.
which updated
<a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>.
That update now states that the server must
send client-id if the client sent it. That is the default behaviour
that Kea offers. However, in some cases older devices that do
not support
<a class="ulink" href="http://tools.ietf.org/html/rfc6842" target="_top">RFC 6842</a>.
may refuse to accept responses that include the
client-id option. To enable backward compatibility, an optional
configuration parameter has been introduced. To configure it,
use the following configuration statement:</p><pre class="screen">
"Dhcp4": {
<strong class="userinput"><code>"echo-client-id": false</code></strong>,
...
}
</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-match-client-id"></a>7.2.18. Using Client Identifier and Hardware Address</h3></div></div></div><p>DHCP server must be able to identify the client (distinguish it from
other clients) from which it receives the message. There are many reasons
why this identification is required and the most important ones are listed
below.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">When the client contacts the server to allocate a new
lease, the server must store the client identification information in
the lease database as a search key.</li><li class="listitem">When the client is trying to renew or release the existing
lease, the server must be able to find the existing lease entry in the
database for this client, using the client identification information as a
search key.</li><li class="listitem">Some configurations use static reservations for the IP
addresses and other configuration information. The server's administrator
uses client identification information to create these static assignments.
</li><li class="listitem">In the dual stack networks there is often a need to
correlate the lease information stored in DHCPv4 and DHCPv6 server for
a particular host. Using common identification information by the DHCPv4
and DHCPv6 client allows the network administrator to achieve this
correlation and better administer the network.</li></ul></div><p>
</p><p>DHCPv4 makes use of two distinct identifiers which are placed
by the client in the queries sent to the server and copied by the server
to its responses to the client: 'chaddr' and 'client identifier'. The
former was introduced as a part of the BOOTP specification and it is also
used by DHCP to carry the hardware address of the interface used to send
the query to the server (MAC address for the Ethernet). The latter is
carried in the Client-identifier option, introduced in the
<a class="ulink" href="http://tools.ietf.org/html/rfc2132" target="_top">RFC 2132</a>.
</p><p>The <a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>
indicates that the server may use both of these identifiers to identify
the client but the 'client identifier', if present, takes precedence
over 'chaddr'. One of the reasons for this is that 'client identifier'
is independent from the hardware used by the client to communicate with
the server. For example, if the client obtained the lease using one
network card and then the network card is moved to another host, the
server will wrongly identify this host is the one which has obtained
the lease. Moreover, the
<a class="ulink" href="https://tools.ietf.org/html/rfc4361" target="_top">RFC 4361</a> gives
the recommendation to use DUID
(see <a class="ulink" href="https://tools.ietf.org/html/rfc3315" target="_top">DHCPv6 specification</a>)
carried as 'client identifier' when dual stack networks are in use,
to provide consistent identification information of the client, regardless
of the protocol type it is using. Kea adheres to these specifications and
the 'client identifier' by default takes precedence over the value carried
in 'chaddr' field when the server searches, creates, updates or removes
the client's lease.
</p><p>When the server receives a DHCPDISCOVER or DHCPREQUEST message from the
client, it will try to find out if the client already has a lease in the
database and will hand out the existing lease rather than allocate
a new one. Each lease in the lease database is associated with the
'client identifier' and/or 'chaddr'. The server will first use the
'client identifier' (if present) to search the lease. If the lease is
found, the server will treat this lease as belonging to the client
even if the current 'chaddr' and the 'chaddr' associated with
the lease do not match. This facilitates the scenario when the network card
on the client system has been replaced and thus the new MAC address
appears in the messages sent by the DHCP client. If the server fails
to find the lease using the 'client identifier' it will perform another lookup
using the 'chaddr'. If this lookup returns no result, the client is
considered as not having a lease and the new lease will be created.
</p><p>A common problem reported by network operators is that bogus
client implementations do not use stable client identifiers such as
generating a new 'client identifier' each time the client connects
to the network. Another well known case is when the client changes its
'client identifier' during the multi-stage boot process (PXE). In such
cases, the MAC address of the client's interface remains stable and
using 'chaddr' field to identify the client guarantees that the
particular system is considered to be the same client, even though its
'client identifier' changes.
</p><p>To address this problem, Kea includes a configuration option
which enables client identification using 'chaddr' only by instructing
the server to disregard server to "ignore" the 'client identifier' during
lease lookups and allocations for a particular subnet. Consider the following
simplified server configuration:</p><pre class="screen">
"Dhcp4": {
...
<strong class="userinput"><code>"match-client-id": true,</code></strong>
...
"subnet4": [
{
"subnet": "192.0.10.0/24",
"pools": [ { "pool": "192.0.2.23-192.0.2.87" } ],
<strong class="userinput"><code>"match-client-id": false</code></strong>
},
{
"subnet": "10.0.0.0/8",
"pools": [ { "pool": "10.0.0.23-10.0.2.99" } ],
}
]
}
</pre><p>The <span class="command"><strong>match-client-id</strong></span> is a boolean value which
controls this behavior. The default value of <strong class="userinput"><code>true</code></strong>
indicates that the server will use the 'client identifier' for lease
lookups and 'chaddr' if the first lookup returns no results. The
<span class="command"><strong>false</strong></span> means that the server will only
use the 'chaddr' to search for client's lease. Whether the DHCID for
DNS updates is generated from the 'client identifier' or 'chaddr' is
controlled through the same parameter accordingly.</p><p>The <span class="command"><strong>match-client-id</strong></span> parameter may appear
both in the global configuration scope and/or under any subnet
declaration. In the example shown above, the effective value of the
<span class="command"><strong>match-client-id</strong></span> will be <strong class="userinput"><code>false</code></strong>
for the subnet 192.0.10.0/24, because the subnet specific setting
of the parameter overrides the global value of the parameter. The
effective value of the <span class="command"><strong>match-client-id</strong></span> for the subnet
10.0.0.0/8 will be set to <strong class="userinput"><code>true</code></strong> because the
subnet declaration lacks this parameter and the global setting is
by default used for this subnet. In fact, the global entry for this
parameter could be omitted in this case, because
<strong class="userinput"><code>true</code></strong> is the default value.
</p><p>It is important to explain what happens when the client obtains
its lease for one setting of the <span class="command"><strong>match-client-id</strong></span>
and then renews when the setting has been changed. Let's first consider
the case when the client obtains the lease when the
<span class="command"><strong>match-client-id</strong></span> is set to <strong class="userinput"><code>true</code></strong>.
The server will store the lease information including 'client identifier'
(if supplied) and 'chaddr' in the lease database. When the setting is
changed and the client renews the lease the server will determine that
it should use the 'chaddr' to search for the existing lease. If the
client hasn't changed its MAC address the server should successfully
find the existing lease. The 'client identifier' associated with the
returned lease is ignored and the client is allowed to use this lease.
When the lease is renewed only the 'chaddr' is recorded for this
lease according to the new server setting.
</p><p>In the second case the client has the lease with only a 'chaddr'
value recorded. When the setting is changed to
<span class="command"><strong>match-client-id</strong></span> set to <strong class="userinput"><code>true</code></strong>
the server will first try to use the 'client identifier' to find the
existing client's lease. This will return no results because the
'client identifier' was not recorded for this lease. The server will
then use the 'chaddr' and the lease will be found. If the lease appears
to have no 'client identifier' recorded, the server will assume that
this lease belongs to the client and that it was created with the previous
setting of the <span class="command"><strong>match-client-id</strong></span>.
However, if the lease contains 'client identifier' which is different
from the 'client identifier' used by the client the lease will be
assumed to belong to another client and the new lease will be
allocated.
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="host-reservation-v4"></a>7.3. Host reservation in DHCPv4</h2></div></div></div><p>There are many cases where it is useful to provide a configuration on
a per host basis. The most obvious one is to reserve specific, static
address for exclusive use by a given client (host) ‐ returning client will
receive the same address from the server every time, and other clients will
generally not receive that address. Note that there may be cases when the
new reservation has been made for the client for the address being currently
in use by another client. We call this situation a "conflict". The conflicts
get resolved automatically over time as described in the subsequent sections.
Once conflict is resolved, the client will keep receiving the reserved
configuration when it renews.</p><p>Another example when the host reservations are applicable is when a host
that has specific requirements, e.g. a printer that needs additional DHCP options.
Yet another possible use case is to define unique names for hosts. Although not all
of the presented use cases are implemented yet, Kea software will support them in the
near future.</p><p>Hosts reservations are defined as parameters for each subnet. Each host
has to be identified by its hardware/MAC address. There is an optional
<span class="command"><strong>reservations</strong></span> array in the <span class="command"><strong>Subnet4</strong></span>
element. Each element in that array is a structure, that holds information
about reservations for a single host. In particular, such a structure has
to have an identifier that uniquely identifies a host. In DHCPv4 context, such an
identifier is a hardware or MAC address. In most cases, also an address
will be specified. It is possible to specify a hostname. Additional
capabilities are planned.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>In Kea 1.0.0 it is only possible to create host reservations
using client's hardware address. Host reservations by client identifier
(or DUID) are not supported in this version of Kea. This capability will
be implemented in Kea 1.1.0. Currently, the configuration parsing code
will accept the "duid" parameter in the reservation configuration, but
the server will misinterpret its value. Therefore, this parameter MUST
NOT be used until the client identifier based host reservations are
properly implemented and documented.</p></div><p>The following example shows how to reserve addresses for specific
hosts:
</p><pre class="screen">
"subnet4": [
{
"pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
"subnet": "192.0.2.0/24",
"interface": "eth0",
<strong class="userinput"><code>"reservations": [
{
"hw-address": "1a:1b:1c:1d:1e:1f",
"ip-address": "192.0.2.202"
},
{
"hw-address": "0a:0b:0c:0d:0e:0f",
"ip-address": "192.0.2.100",
"hostname": "alice-laptop"
}
]</code></strong>
}
]
</pre><p>
The first entry reserves the 192.0.2.202 address for the client that uses
MAC address of 1a:1b:1c:1d:1e:1f. The second entry reserves the address
192.0.2.100 and the hostname of alice-laptop for client using MAC
address 0a:0b:0c:0d:0e:0f. Note that if you plan to do DNS updates, it
is strongly recommended for the hostnames to be unique.
</p><p>Making a reservation for a mobile host that may visit multiple subnets
requires a separate host definition in each subnet it is expected to visit.
It is not allowed to define multiple host definitions with the same hardware
address in a single subnet. It is a valid configuration, if such definitions
are specified in different subnets, though.
</p><p>Adding host reservation incurs a performance penalty. In principle,
when the server that does not support host reservation responds to a query,
it needs to check whether there is a lease for a given address being
considered for allocation or renewal. The server that also supports host
reservation, has to perform additional checks: not only if the address is
currently used (if there is a lease for it), but also whether the address
could be used by someone else (if there is a reservation for it). That
additional check incurs performance penalty.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation4-types"></a>7.3.1. Address reservation types</h3></div></div></div><p>In a typical scenario there is an IPv4 subnet defined,
e.g. 192.0.2.0/24, with certain part of it dedicated for dynamic allocation
by the DHCPv4 server. That dynamic part is referred to as a dynamic pool or
simply a pool. In principle, the host reservation can reserve any address
that belongs to the subnet. The reservations that specify addresses that
belong to configured pools are called <span class="command"><strong>in-pool reservations</strong></span>.
In contrast, those that do not belong to dynamic pools are called
<span class="command"><strong>out-of-pool reservations</strong></span>. There is no formal difference
in the reservation syntax. As of 0.9.1, both reservation types are
handled uniformly. However, upcoming releases may offer improved performance
if there are only out-of-pool reservations as the server will be able
to skip reservation checks when dealing with existing leases. Therefore,
system administrators are encouraged to use out-of-pool reservations, if
possible.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation4-conflict"></a>7.3.2. Conflicts in DHCPv4 reservations</h3></div></div></div><p>As the reservations and lease information are stored separately,
conflicts may arise. Consider the following series of events. The server
has configured the dynamic pool of addresses from the range of 192.0.2.10 to
192.0.2.20. The Host A requests an address and gets 19.0.2.10. Now the system
administrator decides to reserve the address for the Host B. He decides to
reserve 192.0.2.10 for that purpose. In general, reserving an address that
is currently assigned to someone else is not recommended, but there are
valid use cases where such an operation is warranted.</p><p>The server now has a conflict to resolve. Let's analyze the
situation here. If the Host B boots up and requests an address, the server is
not able to assign the reserved address 192.0.2.10 for the Host B. A naive
approach would to be immediately remove the existing lease for the Host A
and create a new one for the Host B. That would not solve the problem,
though, because as soon as the Host B gets the address, it will detect
that the address is already in use by the Host A and would send
the DHCPDECLINE message. Therefore, in this situation, the server has
to temporarily assign a different address (not matching what has been
reserved) to the Host B.</p><p>When the Host A renews its address, the server will discover that
the address being renewed is now reserved for another host - the Host
B. Therefore the server will inform the Host A that it is no longer
allowed to use it by sending DHCPNAK message. The server will not remove the
lease, though, as there's small chance that the DHCPNAK may be lost if the
network is lossy. If that happens, the client will not receive any
responses, so it will retransmit its DHCPREQUEST packet. Once the
DHCPNAK is received by the Host A, it will then revert to the server
discovery and will eventually get a different address. Besides
allocating a new lease, the server will also remove the old one. As
a result, the address 192.0.2.10 will be no longer used. When Host B
tries to renew its temporarily assigned address, the server will detect
that it has a valid lease, but there is a reservation for a different
address. The server will send DHCPNAK to inform Host B that its address
is no longer usable, but will keep its lease (again, the DHCPNAK may be
lost, so the server will keep it, until the client returns for a new
address). The Host B will revert to the server discovery phase and will
eventually send a DHCPREQUEST message. This time the server will find
out that there is a reservation for that host and the reserved address
192.0.2.10 is not used, so it will be granted. It will also remove the
lease for the temporarily assigned address that the Host B previously
obtained.</p><p>This recovery will succeed, even if other hosts will attempt to get
the reserved address. Had the Host C requested address 192.0.2.10 after
the reservation was made, the server will either offer a different
address (when responding to DHCPDISCOVER) or would send DHCPNAK
(when responding to DHCPREQUEST).</p><p>This recovery mechanism allows the server to fully recover from a
case where reservations conflict with the existing leases. This procedure
takes time and will roughly take as long as renew-timer value specified.
The best way to avoid such recovery is to not define new reservations that
conflict with existing leases. Another recommendation is to use
out-of-pool reservations. If the reserved address does not belong to a
pool, there is no way that other clients could get this address (note that
having multiple reservations for the same address is not allowed).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation4-hostname"></a>7.3.3. Reserving a hostname</h3></div></div></div><p>When the reservation for the client includes the <span class="command"><strong>hostname
</strong></span>, the server will assign this hostname to the client and send
it back in the Client FQDN or Hostname option, depending on which of them
the client has sent to the server. The reserved hostname always takes
precedence over the hostname supplied by the client or the autogenerated
(from the IPv4 address) hostname.</p><p>The server qualifies the reserved hostname with the value
of the <span class="command"><strong>qualifying-suffix</strong></span> parameter. For example, the
following subnet configuration:
</p><pre class="screen">
{
"subnet4": [ {
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"hostname": "alice-laptop"
}
]
}],
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example.isc.org."
}
}
</pre><p>
will result in assigning the "alice-laptop.example.isc.org." hostname to the
client using the MAC address "aa:bb:cc:dd:ee:ff". If the <span class="command"><strong>qualifying-suffix
</strong></span> is not specified, the default (empty) value will be used, and
in this case the value specified as a <span class="command"><strong>hostname</strong></span> will
be treated as fully qualified name. Thus, by leaving the
<span class="command"><strong>qualifying-suffix</strong></span> empty it is possible to qualify
hostnames for the different clients with different domain names:
</p><pre class="screen">
{
"subnet4": [ {
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"hostname": "alice-laptop.isc.org."
},
{
"hw-address": "12:34:56:78:99:AA",
"hostname": "mark-desktop.example.org."
}
]
}],
"dhcp-ddns": {
"enable-updates": true,
}
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation4-options"></a>7.3.4. Reserving specific options</h3></div></div></div><p>Currently it is not possible to specify options in host
reservation. Such a feature will be added in the upcoming Kea
releases.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation4-mode"></a>7.3.5. Fine Tuning IPv4 Host Reservation</h3></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><span class="command"><strong>reservation-mode</strong></span> configuration parameter in DHCPv4
server is accepted, but not used in the Kea 0.9.1 beta. Full implementation
will be available in the upcoming releases.</p></div><p>Host reservation capability introduces additional restrictions for the
allocation engine during lease selection and renewal. In particular, three
major checks are necessary. First, when selecting a new lease, it is not
sufficient for a candidate lease to be not used by another DHCP client. It
also must not be reserved for another client. Second, when renewing a lease,
additional check must be performed whether the address being renewed is not
reserved for another client. Finally, when a host renews an address, the server
has to check whether there's a reservation for this host, so the existing
(dynamically allocated) address should be revoked and the reserved one be
used instead.
</p><p>Some of those checks may be unnecessary in certain deployments. Not
performing them may improve performance. The Kea server provides the
<span class="command"><strong>reservation-mode</strong></span> configuration parameter to select the
types of reservations allowed for the particular subnet. Each reservation
type has different constraints for the checks to be performed by the
server when allocating or renewing a lease for the client.
Allowed values are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> <span class="command"><strong>all</strong></span> - enables all host reservation
types. This is the default value. This setting is the safest and the most
flexible. It allows in-pool and out-of-pool reservations. As all checks
are conducted, it is also the slowest.
</li><li class="listitem"> <span class="command"><strong>out-of-pool</strong></span> - allows only out of
pool host reservations. With this setting in place, the server may assume
that all host reservations are for addresses that do not belong to the
dynamic pool. Therefore it can skip the reservation checks when dealing
with in-pool addresses, thus improving performance. Do not use this mode
if any of your reservations use in-pool address. Caution is advised when
using this setting. Kea 0.9.1 does not sanity check the reservations against
<span class="command"><strong>reservation-mode</strong></span>. Misconfiguration may cause problems.
</li><li class="listitem">
<span class="command"><strong>disabled</strong></span> - host reservation support is disabled. As there
are no reservations, the server will skip all checks. Any reservations defined
will be completely ignored. As the checks are skipped, the server may
operate faster in this mode.
</li></ul></div><p>
</p><p>
An example configuration that disables reservation looks like follows:
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
<strong class="userinput"><code>"reservation-mode": "disabled"</code></strong>,
...
}
]
}
</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-serverid"></a>7.4. Server Identifier in DHCPv4</h2></div></div></div><p>
The DHCPv4 protocol uses a "server identifier" to allow clients
to discriminate between several servers present on the same link: this
value is an IPv4 address of the server. The server chooses the IPv4 address
of the interface on which the message from the client (or relay) has been
received. A single server instance will use multiple server identifiers
if it is receiving queries on multiple interfaces.
</p><p>
Currently there is no mechanism to override the default server identifiers
by an administrator. In the future, the configuration mechanism will be used
to specify the custom server identifier.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-subnet-selection"></a>7.5. How the DHCPv4 Server Selects a Subnet for the Client</h2></div></div></div><p>
The DHCPv4 server differentiates between the directly connected clients,
clients trying to renew leases and clients sending their messages through
relays. For the directly connected clients the server will check the
configuration for the interface on which the message has been received, and
if the server configuration doesn't match any configured subnet the
message is discarded.</p><p>Assuming that the server's interface is configured with the
IPv4 address 192.0.2.3, the server will only process messages received through
this interface from a directly connected client if there is a subnet
configured to which this IPv4 address belongs, e.g. 192.0.2.0/24.
The server will use this subnet to assign IPv4 address for the client.
</p><p>
The rule above does not apply when the client unicasts its message, i.e.
is trying to renew its lease. Such a message is accepted through any
interface. The renewing client sets ciaddr to the currently used IPv4
address. The server uses this address to select the subnet for the client
(in particular, to extend the lease using this address).
</p><p>
If the message is relayed it is accepted through any interface. The giaddr
set by the relay agent is used to select the subnet for the client.
</p><p>
It is also possible to specify a relay IPv4 address for a given subnet. It
can be used to match incoming packets into a subnet in uncommon configurations,
e.g. shared subnets. See <a class="xref" href="#dhcp4-relay-override" title="7.5.1. Using a Specific Relay Agent for a Subnet">Section 7.5.1, “Using a Specific Relay Agent for a Subnet”</a> for details.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The subnet selection mechanism described in this section is based
on the assumption that client classification is not used. The classification
mechanism alters the way in which a subnet is selected for the client,
depending on the classes to which the client belongs.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-relay-override"></a>7.5.1. Using a Specific Relay Agent for a Subnet</h3></div></div></div><p>
The relay has to have an interface connected to the link on which
the clients are being configured. Typically the relay has an IPv4
address configured on that interface that belongs to the subnet from which
the server will assign addresses. In the typical case, the
server is able to use the IPv4 address inserted by the relay (in the giaddr
field of the DHCPv4 packet) to select the appropriate subnet.
</p><p>
However, that is not always the case. In certain uncommon —
valid — deployments, the relay address may not match the subnet. This
usually means that there is more than one subnet allocated for a given
link. The two most common examples where this is the case are long lasting
network renumbering (where both old and new address space is still being
used) and a cable network. In a cable network both cable modems and the
devices behind them are physically connected to the same link, yet
they use distinct addressing. In such a case, the DHCPv4 server needs
additional information (the IPv4 address of the relay) to properly select
an appropriate subnet.
</p><p>
The following example assumes that there is a subnet 192.0.2.0/24
that is accessible via a relay that uses 10.0.0.1 as its IPv4 address.
The server will be able to select this subnet for any incoming packets
that came from a relay that has an address in 192.0.2.0/24 subnet.
It will also select that subnet for a relay with address 10.0.0.1.
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
<strong class="userinput"><code>"relay": {
"ip-address": "10.0.0.1"
}</code></strong>,
...
}
],
...
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp4-srv-example-client-class-relay"></a>7.5.2. Segregating IPv4 Clients in a Cable Network</h3></div></div></div><p>
In certain cases, it is useful to mix relay address information,
introduced in <a class="xref" href="#dhcp4-relay-override" title="7.5.1. Using a Specific Relay Agent for a Subnet">Section 7.5.1, “Using a Specific Relay Agent for a Subnet”</a> with client
classification, explained in <a class="xref" href="#classify" title="Chapter 12. Client Classification">Chapter 12, <i>Client Classification</i></a>.
One specific example is cable network, where typically modems
get addresses from a different subnet than all devices connected
behind them.
</p><p>
Let's assume that there is one CMTS (Cable Modem Termination System)
with one CM MAC (a physical link that modems are connected to).
We want the modems to get addresses from the 10.1.1.0/24 subnet, while
everything connected behind modems should get addresses from another
subnet (192.0.2.0/24). The CMTS that acts as a relay uses address
10.1.1.1. The following configuration can serve that configuration:
</p><pre class="screen">
"Dhcp4": {
"subnet4": [
{
"subnet": "10.1.1.0/24",
"pools": [ { "pool": "10.1.1.2 - 10.1.1.20" } ],
<strong class="userinput"><code>"client-class" "docsis3.0",
"relay": {
"ip-address": "10.1.1.1"
}</code></strong>
},
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
<strong class="userinput"><code>"relay": {
"ip-address": "10.1.1.1"
}</code></strong>
}
],
...
}
</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-decline"></a>7.6. Duplicate Addresses (DHCPDECLINE support)</h2></div></div></div><p>The DHCPv4 server is configured with a certain pool of addresses
that it is expected to hand out to the DHCPv4 clients. It is
assumed that the server is authoritative and has complete jurisdiction
over those addresses. However, due to various reasons, such as
misconfiguration or a faulty client implementation that retains its
address beyond the valid lifetime, there may be devices connected that use
those addresses without the server's approval or knowledge.</p><p>Such an
unwelcome event can be detected by legitimate clients (using ARP or ICMP
Echo Request mechanisms) and reported to the DHCPv4 server using a DHCPDECLINE
message. The server will do a sanity check (if the client declining an
address really was supposed to use it), and then will conduct a clean up
operation. Any DNS entries related to that address will be removed, the
fact will be logged and hooks will be triggered. After that is done, the
address will be marked as declined (which indicates that it is used by an
unknown entity and thus not available for assignment to anyone) and a
probation time will be set on it. Unless otherwise configured, the
probation period lasts 24 hours. After that period, the server will
recover the lease, i.e. put it back into the available state. The address will
be available for assignment again. It should be noted that if the
underlying issue of a misconfigured device is not resolved, the duplicate
address scenario will repeat. On the other hand, it provides an
opportunity to recover from such an event automatically, without any
sysadmin intervention.</p><p>To configure the decline probation period to a value different
than the default, the following syntax can be used:
</p><pre class="screen">
"Dhcp4": {
<strong class="userinput"><code>"decline-probation-period": 3600</code></strong>,
"subnet4": [ ... ],
...
}
</pre><p>
The parameter is expressed in seconds, so the example above will instruct
the server to recycle declined leases after an hour.</p><p>There are several statistics and hook points associated with the
Decline handling procedure. The lease4_decline hook is triggered after the
incoming DHCPDECLINE message has been sanitized and the server is about to
decline the lease. The declined-addresses statistic is increased after the
hook returns (both global and subnet specific variants).</p><p>Once the probation time elapses, the declined lease is recovered
using the standard expired lease reclamation procedure, with several
additional steps. In particular, both declined-addresses statistics
(global and subnet specific) are decreased. At the same time,
reclaimed-declined-addresses statistics (again in two variants, global and
subnet specific) are increased.</p><p>Note about statistics: The server does not decrease
assigned-addresses statistics when a DHCPDECLINE is received and processed
successfully. While technically a declined address is no longer assigned,
the primary usage of the assigned-addresses statistic is to monitor pool
utilization. Most people would forget to include declined-addresses in the
calculation, and simply do assigned-addresses/total-addresses. This would
have a bias towards under-representing pool utilization. As this has a
potential for major issues, we decided not to decrease assigned addresses
immediately after receiving DHCPDECLINE, but to do it later when we
recover the address back to the available pool.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-stats"></a>7.7. Statistics in DHCPv4 server</h2></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This section describes DHCPv4-specific statistics. For a general
overview and usage of statistics, see <a class="xref" href="#stats" title="Chapter 14. Statistics">Chapter 14, <i>Statistics</i></a>.</p></div><p>
The DHCPv4 server supports the following statistics:
</p><div class="table"><a name="dhcp4-statistics"></a><p class="title"><b>Table 7.5. DHCPv4 Statistics</b></p><div class="table-contents"><table summary="DHCPv4 Statistics" border="1"><colgroup><col align="center" class="statistic"><col align="center" class="type"><col align="left" class="description"></colgroup><thead><tr><th align="center">Statistic</th><th align="center">Data Type</th><th align="left">Description</th></tr></thead><tbody><tr><td align="center">pkt4-received</td><td align="center">integer</td><td align="left">
Number of DHCPv4 packets received. This includes all packets: valid,
bogus, corrupted, rejected etc. This statistic is expected to grow
rapidly.
</td></tr><tr><td align="center">pkt4-discover-received</td><td align="center">integer</td><td align="left">
Number of DHCPDISCOVER packets received. This statistic is expected to grow.
Its increase means that clients that just booted started their configuration process
and their initial packets reached your server.
</td></tr><tr><td align="center">pkt4-offer-received</td><td align="center">integer</td><td align="left">
Number of DHCPOFFER packets received. This statistic
is expected to remain zero at all times, as DHCPOFFER packets are sent
by the server and the server is never expected to receive them. Non-zero
value indicates an error. One likely cause would be a misbehaving relay
agent that incorrectly forwards DHCPOFFER messages towards the server,
rather back to the clients.
</td></tr><tr><td align="center">pkt4-request-received</td><td align="center">integer</td><td align="left">
Number of DHCPREQUEST packets received. This statistic
is expected to grow. Its increase means that clients that just booted
received server's response (DHCPOFFER), accepted it and now requesting
an address (DHCPREQUEST).
</td></tr><tr><td align="center">pkt4-ack-received</td><td align="center">integer</td><td align="left">
Number of DHCPACK packets received. This statistic
is expected to remain zero at all times, as DHCPACK packets are sent
by the server and the server is never expected to receive them. Non-zero
value indicates an error. One likely cause would be a misbehaving relay
agent that incorrectly forwards DHCPACK messages towards the server,
rather back to the clients.
</td></tr><tr><td align="center">pkt4-nak-received</td><td align="center">integer</td><td align="left">
Number of DHCPNAK packets received. This statistic
is expected to remain zero at all times, as DHCPNAK packets are sent
by the server and the server is never expected to receive them. Non-zero
value indicates an error. One likely cause would be a misbehaving relay
agent that incorrectly forwards DHCPNAK messages towards the server,
rather back to the clients.
</td></tr><tr><td align="center">pkt4-release-received</td><td align="center">integer</td><td align="left">
Number of DHCPRELEASE packets received. This statistic
is expected to grow. Its increase means that clients that had an address
are shutting down or stop using their addresses.
</td></tr><tr><td align="center">pkt4-decline-received</td><td align="center">integer</td><td align="left">
Number of DHCPDECLINE packets received. This statistic
is expected to remain close to zero. Its increase means that a client
that leased an address, but discovered that the address is currently
used by an unknown device in your network.
</td></tr><tr><td align="center">pkt4-inform-received</td><td align="center">integer</td><td align="left">
Number of DHCPINFORM packets received. This statistic
is expected to grow. Its increase means that there are clients that
either do not need an address or already have an address and are
interested only in getting additional configuration parameters.
</td></tr><tr><td align="center">pkt4-unknown-received</td><td align="center">integer</td><td align="left">
Number of packets received of an unknown type. Non-zero
value of this statistic indicates that the server received a packet
that it wasn't able to recognize: either with unsupported type
or possibly malformed (without message type option).
</td></tr><tr><td align="center">pkt4-sent</td><td align="center">integer</td><td align="left">
Number of DHCPv4 packets sent. This statistic is expected to grow
every time the server transmits a packet. In general, it should
roughly match pkt4-received, as most incoming packets cause
server to respond. There are exceptions (e.g. DHCPRELEASE), so
do not worry, if it is lesser than pkt4-received.
</td></tr><tr><td align="center">pkt4-offer-sent</td><td align="center">integer</td><td align="left">
Number of DHCPOFFER packets sent. This statistic is expected to
grow in most cases after a DHCPDISCOVER is processed. There are
certain uncommon, but valid cases where incoming DHCPDISCOVER is
dropped, but in general this statistic is expected to be close to
pkt4-discover-received.
</td></tr><tr><td align="center">pkt4-ack-sent</td><td align="center">integer</td><td align="left">
Number of DHCPACK packets sent. This statistic is expected to
grow in most cases after a DHCPREQUEST is processed. There are
certain cases where DHCPNAK is sent instead. In general, the sum of
pkt4-ack-sent and pkt4-nak-sent should be close to
pkt4-request-received.
</td></tr><tr><td align="center">pkt4-nak-sent</td><td align="center">integer</td><td align="left">
Number of DHCPNAK packets sent. This statistic is expected to
grow when the server choses to not honor the address requested by a
client. In general, the sum of pkt4-ack-sent and pkt4-nak-sent
should be close to pkt4-request-received.
</td></tr><tr><td align="center">pkt4-parse-failed</td><td align="center">integer</td><td align="left">
Number of incoming packets that could not be parsed. Non-zero value of
this statistic indicates that the server received malformed or truncated packet.
This may indicate problems in your network, faulty clients or server code bug.
</td></tr><tr><td align="center">pkt4-receive-drop</td><td align="center">integer</td><td align="left">
Number of incoming packets that were dropped.
Exact reason for dropping packets is logged, but the most common
reasons may be: an unacceptable packet type, direct responses are
forbidden, or the server-id sent by the client does not match
the server's server-id.
</td></tr><tr><td align="center">subnet[id].total-addresses</td><td align="center">integer</td><td align="left">The total number of addresses available for the DHCPv4
management. In other words, this is the sum of all addresses in
all configured pools. This statistic changes only during
configuration changes. Note it does not take into account any
addresses that may be reserved due to host reservation. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately. This statistic is
reset during reconfiguration event.</td></tr><tr><td align="center">subnet[id].assigned-addresses</td><td align="center">integer</td><td align="left">This statistic shows the number of assigned addresses in a
given subnet. This statistic increases every time a new lease is
allocated (as a result of receiving a DHCPREQUEST message) and is
decreased every time a lease is released (a DHCPRELEASE message is
received) or expires. The <span class="emphasis"><em>id</em></span> is the subnet-id
of a given subnet. This statistic is exposed for each subnet
separately. This statistic is reset during reconfiguration event.
</td></tr><tr><td align="center">declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv4 addresses that are
currently declined. This statistic counts the number of leases
currently unavailable. Once a lease is recovered, this
statistic will be decreased. Ideally, this statistic should be
zero. If this statistic is non-zero (or worse increasing),
a network administrator should investigate if there is
a misbehaving device in his network. This is a global statistic
that covers all subnets.
</td></tr><tr><td align="center">subnet[id].declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv4 addresses that are
currently declined in a given subnet. This statistic counts the
number of leases currently unavailable. Once a lease is
recovered, this statistic will be decreased. Ideally, this
statistic should be zero. If this statistic is
non-zero (or worse increasing), a network administrator should
investigate if there is a misbehaving device in his network. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately.
</td></tr><tr><td align="center">reclaimed-declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv4 addresses that were
declined, but have now been recovered. Unlike
declined-addresses, this statistic never decreases. It can be used
as a long term indicator of how many actual valid Declines were
processed and recovered from. This is a global statistic that
covers all subnets.
</td></tr><tr><td align="center">subnet[id].reclaimed-declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv4 addresses that were
declined, but have now been recovered. Unlike
declined-addresses, this statistic never decreases. It can be used
as a long term indicator of how many actual valid Declines were
processed and recovered from. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately.
</td></tr></tbody></table></div></div><br class="table-break"></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-ctrl-channel"></a>7.8. Management API for the DHCPv4 server</h2></div></div></div><p>
Management API has been introduced in Kea 0.9.2-beta. It allows issuing specific
management commands, like statistics retrieval, reconfiguration or shutdown.
For more details, see <a class="xref" href="#ctrl-channel" title="Chapter 15. Management API">Chapter 15, <i>Management API</i></a>. Currently the only
supported communication channel type is UNIX stream socket. By default there
are no sockets open. To instruct Kea to open a socket, the following entry
in the configuration file can be used:
</p><pre class="screen">
"Dhcp4": {
"control-socket": {
"socket-type": "unix",
"socket-name": <strong class="userinput"><code>"/path/to/the/unix/socket"</code></strong>
},
"subnet4": [
...
],
...
}
</pre><p>
</p><p>
The length of the path specified by the <span class="command"><strong>socket-name</strong></span>
parameter is restricted by the maximum length for the unix socket name
on your operating system, i.e. the size of the <span class="command"><strong>sun_path</strong></span>
field in the <span class="command"><strong>sockaddr_un</strong></span> structure, decreased by 1.
This value varies on different operating systems between 91 and 107
characters. The typical values are 107 on Linux and 103 on FreeBSD.
</p><p>
Communication over control channel is conducted using JSON structures.
See the Control Channel section in the Kea Developer's Guide for more details.
</p><p>DHCPv4 server supports <span class="command"><strong>statistic-get</strong></span>,
<span class="command"><strong>statistic-reset</strong></span>, <span class="command"><strong>statistic-remove</strong></span>,
<span class="command"><strong>statistic-get-all</strong></span>, <span class="command"><strong>statistic-reset-all</strong></span>
and <span class="command"><strong>statistic-remove-all</strong></span>, specified in
<a class="xref" href="#command-stats" title="14.3. Commands for Manipulating Statistics">Section 14.3, “Commands for Manipulating Statistics”</a>. It also supports
<span class="command"><strong>list-commands</strong></span> and <span class="command"><strong>shutdown</strong></span>,
specified in <a class="xref" href="#command-list-commands" title="15.3.2. list-commands command">Section 15.3.2, “list-commands command”</a> and
<a class="xref" href="#command-shutdown" title="15.3.3. shutdown command">Section 15.3.3, “shutdown command”</a>, respectively.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-std"></a>7.9. Supported DHCP Standards</h2></div></div></div><p>The following standards are currently supported:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="emphasis"><em>Dynamic Host Configuration Protocol</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>:
Supported messages are DHCPDISCOVER (1), DHCPOFFER (2),
DHCPREQUEST (3), DHCPRELEASE (7), DHCPINFORM (8), DHCPACK (5), and
DHCPNAK(6).</li><li class="listitem"><span class="emphasis"><em>DHCP Options and BOOTP Vendor Extensions</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc2132" target="_top">RFC 2132</a>:
Supported options are: PAD (0),
END(255), Message Type(53), DHCP Server Identifier (54),
Domain Name (15), DNS Servers (6), IP Address Lease Time
(51), Subnet mask (1), and Routers (3).</li><li class="listitem"><span class="emphasis"><em>DHCP Relay Agent Information Option</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc3046" target="_top">RFC 3046</a>:
Relay Agent Information option is supported.</li><li class="listitem"><span class="emphasis"><em>Vendor-Identifying Vendor Options for
Dynamic Host Configuration Protocol version 4</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc3925" target="_top">RFC 3925</a>:
Vendor-Identifying Vendor Class and Vendor-Identifying Vendor-Specific
Information options are supported.</li><li class="listitem"><span class="emphasis"><em>Client Identifier Option in DHCP Server Replies</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc6842" target="_top">RFC 6842</a>:
Server by default sends back client-id option. That capability may be
disabled. See <a class="xref" href="#dhcp4-echo-client-id" title="7.2.17. Echoing Client-ID (RFC 6842)">Section 7.2.17, “Echoing Client-ID (RFC 6842)”</a> for details.
</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp4-limit"></a>7.10. DHCPv4 Server Limitations</h2></div></div></div><p>These are the current limitations of the DHCPv4 server
software. Most of them are reflections of the current stage of
development and should be treated as <span class="quote">“<span class="quote">not implemented
yet</span>”</span>, rather than actual limitations. However, some of them
are implications of the design choices made. Those are clearly
marked as such.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Removal of a subnet during server reconfiguration may cause renumbering
of auto-generated subnet identifiers, as described in section
<a class="xref" href="#ipv4-subnet-id" title="7.2.6. IPv4 Subnet Identifier">Section 7.2.6, “IPv4 Subnet Identifier”</a>.
</li><li class="listitem">Host reservation (static addresses) is not supported yet.</li><li class="listitem">Full featured client classification is not supported yet.</li><li class="listitem">
BOOTP (<a class="ulink" href="http://tools.ietf.org/html/rfc951" target="_top">RFC 951</a>)
is not supported. This is a design choice. BOOTP support is not planned.
</li><li class="listitem">On Linux and BSD system families the DHCP messages are sent
and received over the raw sockets (using LPF and BPF) and all packet
headers (including data link layer, IP and UDP headers) are created and
parsed by Kea, rather than the system kernel. Currently, Kea can
only parse the data link layer headers with a format adhering to
IEEE 802.3 standard and assumes this data link layer header format
for all interfaces. Hence, Kea will fail to work on interfaces
which use different data link layer header formats (e.g. Infiniband).
</li><li class="listitem">The DHCPv4 server does not verify that
assigned address is unused. According to <a class="ulink" href="http://tools.ietf.org/html/rfc2131" target="_top">RFC 2131</a>, the
allocating server should verify that address is not used by
sending ICMP echo request.</li><li class="listitem">Address duplication report (DECLINE) is not supported yet.</li></ul></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="dhcp6"></a>Chapter 8. The DHCPv6 Server</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#dhcp6-start-stop">8.1. Starting and Stopping the DHCPv6 Server</a></span></dt><dt><span class="section"><a href="#dhcp6-configuration">8.2. DHCPv6 Server Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp50920624">8.2.1. Introduction</a></span></dt><dt><span class="section"><a href="#idp55550160">8.2.2. Lease Storage</a></span></dt><dt><span class="section"><a href="#dhcp6-interface-selection">8.2.3. Interface selection</a></span></dt><dt><span class="section"><a href="#ipv6-subnet-id">8.2.4. IPv6 Subnet Identifier</a></span></dt><dt><span class="section"><a href="#dhcp6-unicast">8.2.5. Unicast traffic support</a></span></dt><dt><span class="section"><a href="#dhcp6-address-config">8.2.6. Subnet and Address Pool</a></span></dt><dt><span class="section"><a href="#idp55239488">8.2.7. Subnet and Prefix Delegation Pools</a></span></dt><dt><span class="section"><a href="#dhcp6-std-options">8.2.8. Standard DHCPv6 options</a></span></dt><dt><span class="section"><a href="#dhcp6-custom-options">8.2.9. Custom DHCPv6 options</a></span></dt><dt><span class="section"><a href="#dhcp6-vendor-opts">8.2.10. DHCPv6 vendor specific options</a></span></dt><dt><span class="section"><a href="#dhcp6-option-spaces">8.2.11. Nested DHCPv6 options (custom option spaces)</a></span></dt><dt><span class="section"><a href="#dhcp6-option-data-defaults">8.2.12. Unspecified parameters for DHCPv6 option configuration</a></span></dt><dt><span class="section"><a href="#dhcp6-config-subnets">8.2.13. IPv6 Subnet Selection</a></span></dt><dt><span class="section"><a href="#dhcp6-rapid-commit">8.2.14. Rapid Commit</a></span></dt><dt><span class="section"><a href="#dhcp6-relays">8.2.15. DHCPv6 Relays</a></span></dt><dt><span class="section"><a href="#dhcp6-rsoo">8.2.16. Relay-Supplied Options</a></span></dt><dt><span class="section"><a href="#dhcp6-client-classifier">8.2.17. Client Classification in DHCPv6</a></span></dt><dt><span class="section"><a href="#dhcp6-ddns-config">8.2.18. Configuring DHCPv6 for DDNS</a></span></dt></dl></dd><dt><span class="section"><a href="#host-reservation-v6">8.3. Host reservation in DHCPv6</a></span></dt><dd><dl><dt><span class="section"><a href="#reservation6-types">8.3.1. Address/prefix reservation types</a></span></dt><dt><span class="section"><a href="#reservation6-conflict">8.3.2. Conflicts in DHCPv6 reservations</a></span></dt><dt><span class="section"><a href="#reservation6-hostname">8.3.3. Reserving a hostname</a></span></dt><dt><span class="section"><a href="#reservation6-options">8.3.4. Reserving specific options</a></span></dt><dt><span class="section"><a href="#reservation6-mode">8.3.5. Fine Tuning IPv6 Host Reservation</a></span></dt></dl></dd><dt><span class="section"><a href="#dhcp6-serverid">8.4. Server Identifier in DHCPv6</a></span></dt><dt><span class="section"><a href="#stateless-dhcp6">8.5. Stateless DHCPv6 (Information-Request Message)</a></span></dt><dt><span class="section"><a href="#dhcp6-rfc7550">8.6. Support for RFC 7550</a></span></dt><dt><span class="section"><a href="#dhcp6-relay-override">8.7. Using specific relay agent for a subnet</a></span></dt><dt><span class="section"><a href="#dhcp6-client-class-relay">8.8. Segregating IPv6 clients in a cable network</a></span></dt><dt><span class="section"><a href="#mac-in-dhcpv6">8.9. MAC/Hardware addresses in DHCPv6</a></span></dt><dt><span class="section"><a href="#dhcp6-decline">8.10. Duplicate Addresses (DECLINE support)</a></span></dt><dt><span class="section"><a href="#dhcp6-stats">8.11. Statistics in DHCPv6 server</a></span></dt><dt><span class="section"><a href="#dhcp6-ctrl-channel">8.12. Management API for the DHCPv6 server</a></span></dt><dt><span class="section"><a href="#dhcp6-std">8.13. Supported DHCPv6 Standards</a></span></dt><dt><span class="section"><a href="#dhcp6-limit">8.14. DHCPv6 Server Limitations</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-start-stop"></a>8.1. Starting and Stopping the DHCPv6 Server</h2></div></div></div><p>
It is recommended that the Kea DHCPv6 server be started and stopped
using <span class="command"><strong>keactrl</strong></span> (described in <a class="xref" href="#keactrl" title="Chapter 6. Managing Kea with keactrl">Chapter 6, <i>Managing Kea with keactrl</i></a>).
However, it is also possible to run the server directly: it accepts
the following command-line switches:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>-c <em class="replaceable"><code>file</code></em></strong></span> -
specifies the configuration file. This is the only mandatory
switch.</li><li class="listitem">
<span class="command"><strong>-d</strong></span> - specifies whether the server
logging should be switched to verbose mode. In verbose mode,
the logging severity and debuglevel specified in the configuration
file are ignored and "debug" severity and the maximum debuglevel
(99) are assumed. The flag is convenient, for temporarily
switching the server into maximum verbosity, e.g. when
debugging.</li><li class="listitem">
<span class="command"><strong>-p <em class="replaceable"><code>port</code></em></strong></span> -
specifies UDP port on which the server will listen. This is only
useful during testing, as a DHCPv6 server listening on
ports other than default DHCPv6 ports will not be able to
handle regular DHCPv6 queries.</li><li class="listitem">
<span class="command"><strong>-v</strong></span> - prints out Kea version and exits.
</li><li class="listitem">
<span class="command"><strong>-V</strong></span> - prints out Kea extended version with
additional parameters and exits.
</li><li class="listitem">
<span class="command"><strong>-W</strong></span> - prints out Kea configuration report
and exits.
</li></ul></div><p>
The <span class="command"><strong>-V</strong></span> command returns the versions of the
external libraries dynamically linked.
</p><p>
The <span class="command"><strong>-W</strong></span> command describes the environment used
to build Kea. This command displays a copy of the
<code class="filename">config.report</code> file produced by
<strong class="userinput"><code>./configure</code></strong> that is embedded in the
executable binary.
</p><p>
The <code class="filename">config.report</code> may also be accessed more
directly. The following command may be used to extract this
information. The binary <strong class="userinput"><code>path</code></strong> may be found
in the install directory or in the <code class="filename">.libs</code>
subdirectory in the source tree. For example
<code class="filename">kea/src/bin/dhcp6/.libs/kea-dhcp6</code>.
</p><pre class="screen">
strings <strong class="userinput"><code>path</code></strong>/kea-dhcp6 | sed -n 's/;;;; //p'
</pre><p>
</p><p>
When running in a console, the server can be shut down by
pressing ctrl-c. It detects the key combination and shuts
down gracefully.
</p><p>
On start-up, the server will detect available network interfaces
and will attempt to open UDP sockets on all interfaces
mentioned in the configuration file.
</p><p>
Since the DHCPv6 server opens privileged ports, it requires root
access. Make sure you run this daemon as root.
</p><p>
During startup the server will attempt to create a PID file of the
form: [localstatedir]/[conf name].kea-dhcp6.pid
where:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>localstatedir</strong></span>: The value as passed into the
build configure script. It defaults to "/usr/local/var". Note
that this value may be overridden at run time by setting the environment
variable KEA_PIDFILE_DIR. This is intended primarily for testing purposes.
</li><li class="listitem"><span class="command"><strong>conf name</strong></span>: The configuration file name
used to start the server, minus all preceding path and file extension.
For example, given a pathname of "/usr/local/etc/kea/myconf.txt", the
portion used would be "myconf".
</li></ul></div><p>
If the file already exists and contains the PID of a live process,
the server will issue a DHCP6_ALREADY_RUNNING log message and exit. It
is possible, though unlikely, that the file is a remnant of a system crash
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-configuration"></a>8.2. DHCPv6 Server Configuration</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp50920624"></a>8.2.1. Introduction</h3></div></div></div><p>
This section explains how to configure the DHCPv6 server using the
Kea configuration backend. (Kea configuration using any other
backends is outside of scope of this document.) Before DHCPv6
is started, its configuration file has to be created. The
basic configuration looks as follows:
</p><pre class="screen">
{
# DHCPv6 configuration starts on the next line
"Dhcp6": {
# First we set up global values
"renew-timer": 1000,
"rebind-timer": 2000,
"preferred-lifetime": 3000,
"valid-lifetime": 4000,
# Next we setup the interfaces to be used by the server.
"interfaces-config": {
"interfaces": [ "eth0" ]
},
# And we specify the type of a lease database
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/var/kea/dhcp6.leases"
},
# Finally, we list the subnets from which we will be leasing addresses.
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
]
}
]
# DHCPv6 configuration ends with the next line
}
} </pre><p>
</p><p>The following paragraphs provide a brief overview of the parameters in
the above example and
their format. Subsequent sections of this chapter go into much greater detail
for these and other parameters.</p><p>The lines starting with a hash (#) are comments and are ignored by
the server; they do not impact its
operation in any way.</p><p>The configuration starts in the first line with the initial
opening curly bracket (or brace). Each configuration consists of
one or more objects. In this specific example, we have only one
object called Dhcp6. This is a simplified configuration, as usually
there will be additional objects, like <span class="command"><strong>Logging</strong></span> or
<span class="command"><strong>DhcpDns</strong></span>, but we omit them now for clarity. The Dhcp6
configuration starts with the <span class="command"><strong>"Dhcp6": {</strong></span> line
and ends with the corresponding closing brace (in the above example,
the brace after the last comment). Everything defined between those
lines is considered to be the Dhcp6 configuration.</p><p>In the general case, the order in which those parameters appear does not
matter. There are two caveats here though. The first one is to remember that
the configuration file must be well formed JSON. That means that parameters
for any given scope must be separated by a comma and there must not be a comma
after the last parameter. When reordering a configuration file, keep in mind that
moving a parameter to or from the last position in a given scope may require
moving the comma as well. The second caveat is that it is uncommon — although
legal JSON — to
repeat the same parameter multiple times. If that happens, the last occurrence of a
given parameter in a given scope is used while all previous instances are
ignored. This is unlikely to cause any confusion as there are no real life
reasons to keep multiple copies of the same parameter in your configuration
file.</p><p>Moving onto the DHCPv6 configuration elements, the very first few elements
define some global parameters. <span class="command"><strong>valid-lifetime</strong></span>
defines for how long the addresses (leases) given out by the server are valid. If
nothing changes, a client that got an address is allowed to use it for 4000
seconds. (Note that integer numbers are specified as is, without any quotes
around them.) The address will become deprecated in 3000 seconds (clients are
allowed to keep old connections, but can't use this address for creating new
connections). <span class="command"><strong>renew-timer</strong></span> and <span class="command"><strong>
rebind-timer</strong></span> are values that define T1 and T2 timers that govern when
the client will begin the renewal and rebind procedures.</p><p>The <span class="command"><strong>interfaces-config</strong></span> map specifies the server
configuration concerning the network interfaces, on which the server should
listen to the DHCP messages. The <span class="command"><strong>interfaces</strong></span> parameter
specifies a list of network interfaces on which the server should listen.
Lists are opened and closed with square brackets, with elements separated
by commas. Had we wanted to listen on two interfaces, the
<span class="command"><strong>interfaces-config</strong></span> would look like this:
</p><pre class="screen">
"interfaces-config": {
"interfaces": [ "eth0", "eth1" ]
},
</pre><p>
</p><p>The next couple of lines define the lease database, the place where the server
stores its lease information. This particular example tells the server to use
<span class="command"><strong>memfile</strong></span>, which is the simplest (and fastest) database
backend. It uses an in-memory database and stores leases on disk in a CSV
file. This is a very simple configuration. Usually, lease database configuration
is more extensive and contains additional parameters. Note that
<span class="command"><strong>lease-database</strong></span>
is an object and opens up a new scope, using an opening brace.
Its parameters (just one in this example -- <span class="command"><strong>type</strong></span>)
follow. Had there been more than one, they would be separated by commas. This
scope is closed with a closing brace. As more parameters follow, a trailing
comma is present.</p><p>Finally, we need to define a list of IPv6 subnets. This is the
most important DHCPv6 configuration structure as the server uses that
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
specified with the <span class="command"><strong>subnet6</strong></span> parameter. It is a list,
so it starts and ends with square brackets. Each subnet definition in
the list has several attributes associated with it, so it is a structure
and is opened and closed with braces. At minimum, a subnet definition
has to have at least two parameters: <span class="command"><strong>subnet</strong></span> (that
defines the whole subnet) and <span class="command"><strong>pool</strong></span> (which is a list of
dynamically allocated pools that are governed by the DHCP server).</p><p>The example contains a single subnet. Had more than one been defined,
additional elements
in the <span class="command"><strong>subnet6</strong></span> parameter would be specified and
separated by commas. For example, to define two subnets, the following
syntax would be used:
</p><pre class="screen">
"subnet6": [
{
"pools": [
{
"pool": "2001:db8:1::/112"
}
],
"subnet": "2001:db8:1::/64"
},
{
"pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
"subnet": "2001:db8:2::/64",
"interface": "eth0"
}
]
</pre><p>
Note that indentation is optional and is used for aesthetic purposes only.
In some cases in may be preferable to use more compact notation.
</p><p>After all parameters are specified, we have two contexts open:
global and Dhcp6, hence we need two closing curly brackets to close them.
In a real life configuration file there most likely would be additional
components defined such as Logging or DhcpDdns, so the closing brace would
be followed by a comma and another object definition.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp55550160"></a>8.2.2. Lease Storage</h3></div></div></div><p>All leases issued by the server are stored in the lease database.
Currently there are three database backends available:
memfile (which is the default backend), MySQL and PostgreSQL.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp55551520"></a>8.2.2.1. Memfile, Basic Storage for Leases</h4></div></div></div><p>The server is able to store lease data in different repositories. Larger
deployments may elect to store leases in a database. <a class="xref" href="#database-configuration6" title="8.2.2.2. Lease Database Configuration">Section 8.2.2.2, “Lease Database Configuration”</a> describes this option. In typical
smaller deployments though, the server will use a CSV file rather than a database to
store lease information. As well as requiring less administration, an
advantage of using a file for storage is that it
eliminates a dependency on third-party database software.</p><p>The configuration of the file backend (Memfile) is controlled through
the Dhcp6/lease-database parameters. The <span class="command"><strong>type</strong></span> parameter
is mandatory and it specifies which storage for leases the server should use.
The value of <strong class="userinput"><code>"memfile"</code></strong> indicates that the file should
be used as the storage. The following list presents the remaining, not mandatory
parameters, which can be used to configure the Memfile backend.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>persist</strong></span>: controls whether the new leases and
updates to existing leases are written to the file. It is strongly
recommended that the value of this parameter is set to
<strong class="userinput"><code>true</code></strong> at all times, during the server's normal
operation. Not writing leases to disk will mean that if a server is restarted
(e.g. after a power failure), it will not know what addresses have been
assigned. As a result, it may hand out addresses to new clients that are
already in use. The value of <strong class="userinput"><code>false</code></strong> is mostly useful
for performance testing purposes. The default value of the
<span class="command"><strong>persist</strong></span> parameter is <strong class="userinput"><code>true</code></strong>,
which enables writing lease updates
to the lease file.
</li><li class="listitem"><span class="command"><strong>name</strong></span>: specifies an absolute location of the lease
file in which new leases and lease updates will be recorded. The default value
for this parameter is <strong class="userinput"><code>"[kea-install-dir]/var/kea/kea-leases6.csv"
</code></strong>.</li><li class="listitem"><span class="command"><strong>lfc-interval</strong></span>: specifies the interval in seconds, at
which the server (Memfile backend) will perform a lease file cleanup (LFC),
which removes the redundant (historical) information from the lease file
and effectively reduces the lease file size. The cleanup process is described
in more detailed fashion further in this section. The default value of the
<span class="command"><strong>lfc-interval</strong></span> is <strong class="userinput"><code>0</code></strong>, which disables
the LFC.</li></ul></div><p>
</p><p>The example configuration of the Memfile backend is presented below:
</p><pre class="screen">
"Dhcp6": {
"lease-database": {
<strong class="userinput"><code>"type": "memfile"</code></strong>,
<strong class="userinput"><code>"persist": true</code></strong>,
<strong class="userinput"><code>"name": "/tmp/kea-leases6.csv"</code></strong>,
<strong class="userinput"><code>"lfc-interval": 1800</code></strong>
}
}
</pre><p>
</p><p>It is important to know how the lease file contents are organized
to understand why the periodic lease file cleanup is needed. Every time when
the server updates a lease or creates a new lease for the client, the new
lease information must be recorded in the lease file. For performance reasons,
the server does not supersede the existing client's lease, as it would require
the lookup of the specific lease entry, but simply appends the new lease
information at the end of the lease file. The previous lease entries for the
client are not removed. When the server loads leases from the lease file, e.g.
at the server startup, it assumes that the latest lease entry for the client
is the valid one. The previous entries are discarded. This means that the
server can re-construct the accurate information about the leases even though
there may be many lease entries for each client. However, storing many entries
for each client results in bloated lease file and impairs the performance of
the server's startup and reconfiguration, as it needs to process larger number
of lease entries.
</p><p>The lease file cleanup removes all previous entries for each client and
leaves only the latest ones. The interval at which the cleanup is performed
is configurable, and it should be selected according to the frequency of lease
renewals initiated by the clients. The more frequent renewals are, the lesser
value of the <span class="command"><strong>lfc-interval</strong></span> should be. Note however, that the
LFC takes time and thus it is possible (although unlikely) that new cleanup
is started while the previous cleanup instance is still running, if the
<span class="command"><strong>lfc-interval</strong></span> is too short. The server would recover from
this by skipping the new cleanup when it detects that the previous cleanup
is still in progress. But, this implies that the actual cleanups will be
triggered more rarely than configured. Moreover, triggering a new cleanup
adds an overhead to the server, which will not be able to respond to new
requests for a short period of time when the new cleanup process is spawned.
Therefore, it is recommended that the <span class="command"><strong>lfc-interval</strong></span> value
is selected in a way that would allow for completing the cleanup before the
new cleanup is triggered.
</p><p>The LFC is performed by a separate process (in background) to avoid
performance impact on the server process. In order to avoid the conflicts
between the two processes both using the same lease files, the LFC process
operates on the copy of the original lease file, rather than on the lease
file used by the server to record lease updates. There are also other files
being created as a side effect of the lease file cleanup. The detailed
description of the LFC is located on the Kea wiki:
<a class="ulink" href="http://kea.isc.org/wiki/LFCDesign" target="_top">http://kea.isc.org/wiki/LFCDesign</a>.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="database-configuration6"></a>8.2.2.2. Lease Database Configuration</h4></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Lease database access information must be configured for the DHCPv6 server,
even if it has already been configured for the DHCPv4 server. The servers
store their information independently, so each server can use a separate
database or both servers can use the same database.</p></div><p>Lease database configuration is controlled through the
Dhcp6/lease-database parameters. The type of the database must be set to
"memfile", "mysql" or "postgresql", e.g.
</p><pre class="screen">
"Dhcp6": { "lease-database": { <strong class="userinput"><code>"type": "mysql"</code></strong>, ... }, ... }
</pre><p>
Next, the name of the database is to hold the leases must be set: this is the
name used when the lease database was created (see <a class="xref" href="#mysql-database-create" title="4.3.2.1. First Time Creation of Kea Database">Section 4.3.2.1, “First Time Creation of Kea Database”</a>
or <a class="xref" href="#pgsql-database-create" title="4.3.3.1. Manually Create the PostgreSQL Database and the Kea User">Section 4.3.3.1, “Manually Create the PostgreSQL Database and the Kea User”</a>).
</p><pre class="screen">
"Dhcp6": { "lease-database": { <strong class="userinput"><code>"name": "<em class="replaceable"><code>database-name</code></em>" </code></strong>, ... }, ... }
</pre><p>
If the database is located on a different system than the DHCPv6 server, the
database host name must also be specified (although it should be noted that this
configuration may have a severe impact on server performance):
</p><pre class="screen">
"Dhcp6": { "lease-database": { <strong class="userinput"><code>"host": <em class="replaceable"><code>remote-host-name</code></em></code></strong>, ... }, ... }
</pre><p>
The usual state of affairs will be to have the database on the same machine as
the DHCPv6 server. In this case, set the value to the empty string:
</p><pre class="screen">
"Dhcp6": { "lease-database": { <strong class="userinput"><code>"host" : ""</code></strong>, ... }, ... }
</pre><p>
</p><p>Finally, the credentials of the account under which the server will
access the database should be set:
</p><pre class="screen">
"Dhcp6": { "lease-database": { <strong class="userinput"><code>"user": "<em class="replaceable"><code>user-name</code></em>"</code></strong>,
<strong class="userinput"><code>"password": "<em class="replaceable"><code>password</code></em>"</code></strong>,
... },
... }
</pre><p>
If there is no password to the account, set the password to the empty string
"". (This is also the default.)</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-interface-selection"></a>8.2.3. Interface selection</h3></div></div></div><p>The DHCPv6 server has to be configured to listen on specific network
interfaces. The simplest network interface configuration instructs the server to
listen on all available interfaces:
</p><pre class="screen">
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"*"</code></strong> ]
}
...
}
</pre><p>
The asterisk plays the role of a wildcard and means "listen on all interfaces".
However, it is usually a good idea to explicitly specify interface names:
</p><pre class="screen">
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1", "eth3"</code></strong> ]
},
...
}
</pre><p>
</p><p>It is possible to use wildcard interface name (asterisk) concurrently
with the actual interface names:
</p><pre class="screen">
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1", "eth3", "*"</code></strong> ]
},
...
}
</pre><p>
It is anticipated that this will form of usage only be used where it is desired to
temporarily override a list of interface names and listen on all interfaces.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="ipv6-subnet-id"></a>8.2.4. IPv6 Subnet Identifier</h3></div></div></div><p>
The subnet identifier is a unique number associated with a particular subnet.
In principle, it is used to associate clients' leases with respective subnets.
When the subnet identifier is not specified for a subnet being configured, it will
be automatically assigned by the configuration mechanism. The identifiers
are assigned from 1 and are monotonically increased for each subsequent
subnet: 1, 2, 3 ....
</p><p>
If there are multiple subnets configured with auto-generated identifiers and
one of them is removed, the subnet identifiers may be renumbered. For example:
if there are four subnets and the third is removed the last subnet will be assigned
the identifier that the third subnet had before removal. As a result, the leases
stored in the lease database for subnet 3 are now associated with
subnet 4, which may have unexpected consequences. In the future it is planned
to implement a mechanism to preserve auto-generated subnet ids upon removal
of one of the subnets. Currently, the only remedy for this issue is to
manually specify a unique subnet identifier for each subnet.
</p><p>
The following configuration will assign the specified subnet
identifier to the newly configured subnet:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
<strong class="userinput"><code>"id": 1024</code></strong>,
...
}
]
}
</pre><p>
This identifier will not change for this subnet unless the "id" parameter is
removed or set to 0. The value of 0 forces auto-generation of the subnet
identifier.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-unicast"></a>8.2.5. Unicast traffic support</h3></div></div></div><p>
When the DHCPv6 server starts, by default it listens to the DHCP traffic
sent to multicast address ff02::1:2 on each interface that it is
configured to listen on (see <a class="xref" href="#dhcp6-interface-selection" title="8.2.3. Interface selection">Section 8.2.3, “Interface selection”</a>).
In some cases it is useful to configure a server to handle incoming
traffic sent to the global unicast addresses as well. The most common
reason for that is to have relays send their traffic to the server
directly. To configure the server to listen on a specific unicast address, the
notation to specify interfaces has been extended. An interface name can be
optionally followed by a slash, followed by the global unicast address on which
the server should listen. This will be done in addition to normal
link-local binding + listening on ff02::1:2 address. The sample configuration
below shows how to listen on 2001:db8::1 (a global address)
configured on the eth1 interface.
</p><p>
</p><pre class="screen">
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <strong class="userinput"><code>"eth1/2001:db8::1"</code></strong> ]
},
...
}
</pre><p>
This configuration will cause the server to listen on
eth1 on link-local address, multicast group (ff02::1:2) and 2001:db8::1.
</p><p>
It is possible to mix interface names, wildcards and interface name/addresses
on the list of interfaces. It is not possible to specify more than one
unicast address on a given interface.
</p><p>
Care should be taken to specify proper unicast addresses. The server will
attempt to bind to those addresses specified, without any additional checks.
This approach is selected on purpose, so the software can be used to
communicate over uncommon addresses if the administrator so desires.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-address-config"></a>8.2.6. Subnet and Address Pool</h3></div></div></div><p>
The essential role of a DHCPv6 server is address assignment. For this,
the server has to be configured with at least one subnet and one pool of dynamic
addresses to be managed. For example, assume that the server
is connected to a network segment that uses the 2001:db8:1::/64
prefix. The Administrator of that network has decided that addresses from range
2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6
server. Such a configuration can be achieved in the following way:
</p><pre class="screen">
"Dhcp6": {
<strong class="userinput"><code>"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
...
}
]</code></strong>
}</pre><p>
Note that subnet is defined as a simple string, but the pool parameter
is actually a list of pools: for this reason, the pool definition is
enclosed in square brackets, even though only one range of addresses
is specified.</p><p>Each <span class="command"><strong>pool</strong></span> is a structure that contains the
parameters that describe a single pool. Currently there is only one
parameter, <span class="command"><strong>pool</strong></span>, which gives the range of addresses
in the pool. Additional parameters will be added in future releases of
Kea.</p><p>It is possible to define more than one pool in a
subnet: continuing the previous example, further assume that
2001:db8:1:0:5::/80 should also be managed by the server. It could be written as
2001:db8:1:0:5:: to 2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's
is cumbersome. It can be expressed more simply as 2001:db8:1:0:5::/80. Both
formats are supported by Dhcp6 and can be mixed in the pool list.
For example, one could define the following pools:
</p><pre class="screen">
"Dhcp6": {
<strong class="userinput"><code>"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{ "pool": "2001:db8:1::1-2001:db8:1::ffff" },
{ "pool": "2001:db8:1:05::/80" }
]</code></strong>,
...
}
]
}</pre><p>
The number of pools is not limited, but for performance reasons it is recommended to
use as few as possible.
</p><p>
The server may be configured to serve more than one subnet. To add a second subnet,
use a command similar to the following:
</p><pre class="screen">
"Dhcp6": {
<strong class="userinput"><code>"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{ "pool": "2001:db8:1::1-2001:db8:1::ffff" }
]
},
{
"subnet": "2001:db8:2::/64",
"pools": [
{ "pool": "2001:db8:2::/64" }
]
},
</code></strong>
...
]
}</pre><p>
In this example, we allow the server to
dynamically assign all addresses available in the whole subnet. Although
rather wasteful, it is certainly a valid configuration to dedicate the
whole /64 subnet for that purpose. Note that the Kea server does not preallocate
the leases, so there is no danger in using gigantic address pools.
</p><p>
When configuring a DHCPv6 server using prefix/length notation, please pay
attention to the boundary values. When specifying that the server can use
a given pool, it will also be able to allocate the first (typically network
address) address from that pool. For example for pool 2001:db8:2::/64 the
2001:db8:2:: address may be assigned as well. If you want to avoid this,
use the "min-max" notation.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp55239488"></a>8.2.7. Subnet and Prefix Delegation Pools</h3></div></div></div><p>
Subnets may also be configured to delegate prefixes, as defined in
<a class="ulink" href="http://tools.ietf.org/html/rfc3633" target="_top">RFC 3633</a>.
A subnet may have one or more prefix delegation pools. Each pool has
a prefixed address, which is specified as a prefix and a prefix length,
as well as a delegated prefix length. <span class="command"><strong>delegated-len</strong></span>
must not be shorter (that is it must be numerically greater or equal)
than <span class="command"><strong>prefix-len</strong></span>.
If both <span class="command"><strong>delegated-len</strong></span>
and <span class="command"><strong>prefix-len</strong></span> are equal, the server will be able to
delegate only one prefix. The delegated <span class="command"><strong>prefix</strong></span> does
not have to match the <span class="command"><strong>subnet</strong></span> prefix.
</p><p> Below is a sample subnet configuration which enables prefix
delegation for the subnet:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:d8b:1::/64",
<strong class="userinput"><code>"pd-pools": [
{
"prefix": "3000:1::",
"prefix-len": 64,
"delegated-len": 96
}
]</code></strong>
}
],
...
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-std-options"></a>8.2.8. Standard DHCPv6 options</h3></div></div></div><p>
One of the major features of a DHCPv6 server is to provide configuration
options to clients. Although there are several options that require
special behavior, most options are sent by the server only if the client
explicitly requests them. The following example shows how to
configure DNS servers, which is one of the most frequently used
options. Numbers in the first column are added for easier reference and
will not appear on screen. Options specified in this way are considered
global and apply to all configured subnets.
</p><pre class="screen">
"Dhcp6": {
"option-data": [
{
<strong class="userinput"><code>"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8::cafe, 2001:db8::babe"</code></strong>
},
...
]
}
</pre><p>
</p><p>
The <span class="command"><strong>option-data></strong></span> line creates a new entry in
the option-data table. This table contains
information on all global options that the server is supposed to configure
in all subnets. The <span class="command"><strong>name</strong></span> line specifies the option name.
(For a complete list
of currently supported names, see <a class="xref" href="#dhcp6-std-options-list" title="Table 8.1. List of standard DHCPv6 options">Table 8.1, “List of standard DHCPv6 options”</a>.) The next line specifies the option code,
which must match one of the values from that list. The line beginning with
<span class="command"><strong>space</strong></span> specifies the option space, which must always be set
to "dhcp6" as these are standard DHCPv6 options. For other name spaces,
including custom option spaces, see <a class="xref" href="#dhcp6-option-spaces" title="8.2.11. Nested DHCPv6 options (custom option spaces)">Section 8.2.11, “Nested DHCPv6 options (custom option spaces)”</a>. The next line specifies the format in
which the data will be entered: use of CSV (comma separated values) is
recommended. The <span class="command"><strong>data</strong></span> line gives the actual value to be sent to
clients. Data is specified as normal text, with values separated by
commas if more than one value is allowed.
</p><p>
Options can also be configured as hexadecimal values. If "csv-format" is
set to false, the option data must be specified as a string of hexadecimal
numbers. The
following commands configure the DNS-SERVERS option for all
subnets with the following addresses: 2001:db8:1::cafe and
2001:db8:1::babe.
</p><pre class="screen">
"Dhcp6": {
"option-data": [
{
<strong class="userinput"><code>"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": false,
"data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
2001 0DB8 0001 0000 0000 0000 0000 BABE"</code></strong>
},
...
]
}
</pre><p>
The value for the setting of the "data" element is split across two
lines in this document for clarity: when entering the command, the
whole string should be entered on the same line. Care should be taken
to use proper encoding when using hexadecimal format as Kea's ability
to validate data correctness in hexadecimal is limited.
</p><p>
Most of the parameters in the "option-data" structure are optional and
can be omitted in some circumstances as discussed in the
<a class="xref" href="#dhcp6-option-data-defaults" title="8.2.12. Unspecified parameters for DHCPv6 option configuration">Section 8.2.12, “Unspecified parameters for DHCPv6 option configuration”</a>.
</p><p>
It is possible to override options on a per-subnet basis. If
clients connected to most of your subnets are expected to get the
same values of a given option, you should use global options: you
can then override specific values for a small number of subnets.
On the other hand, if you use different values in each subnet,
it does not make sense to specify global option values
(Dhcp6/option-data), rather you should set only subnet-specific values
(Dhcp6/subnet[X]/option-data[Y]).
</p><p>
The following commands override the global
DNS servers option for a particular subnet, setting a single DNS
server with address 2001:db8:1::3.
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
<strong class="userinput"><code>"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:1::3"
},
...
]</code></strong>,
...
},
...
],
...
}
</pre><p>
</p><p>
The currently supported standard DHCPv6 options are
listed in <a class="xref" href="#dhcp6-std-options-list" title="Table 8.1. List of standard DHCPv6 options">Table 8.1, “List of standard DHCPv6 options”</a>.
The "Name" and "Code"
are the values that should be used as a name in the option-data
structures. "Type" designates the format of the data: the meanings of
the various types is given in <a class="xref" href="#dhcp-types" title="Table 7.3. List of standard DHCP option types">Table 7.3, “List of standard DHCP option types”</a>.
</p><p>
Experimental options (like standard options but with a code
which was not assigned by IANA) are listed in
<a class="xref" href="#dhcp6-exp-options-list" title="Table 8.2. List of experimental DHCPv6 options">Table 8.2, “List of experimental DHCPv6 options”</a>.
</p><p>
Some options are designated as arrays, which means that more than one
value is allowed in such an option. For example the option dns-servers
allows the specification of more than one IPv6 address, allowing
clients to obtain the addresses of multiple DNS servers.
</p><p>
The <a class="xref" href="#dhcp6-custom-options" title="8.2.9. Custom DHCPv6 options">Section 8.2.9, “Custom DHCPv6 options”</a> describes the configuration
syntax to create custom option definitions (formats). It is generally not
allowed to create custom definitions for standard options, even if the
definition being created matches the actual option format defined in the
RFCs. There is an exception from this rule for standard options for which
Kea does not provide a definition yet. In order to use such options,
a server administrator must create a definition as described in
<a class="xref" href="#dhcp6-custom-options" title="8.2.9. Custom DHCPv6 options">Section 8.2.9, “Custom DHCPv6 options”</a> in the 'dhcp6' option space. This
definition should match the option format described in the relevant
RFC but the configuration mechanism would allow any option format as it has
no means to validate the format at the moment.
</p><p>
</p><div class="table"><a name="dhcp6-std-options-list"></a><p class="title"><b>Table 8.1. List of standard DHCPv6 options</b></p><div class="table-contents"><table summary="List of standard DHCPv6 options" border="1"><colgroup><col class="name"><col align="center" class="code"><col align="center" class="type"><col align="center" class="array"></colgroup><thead><tr><th>Name</th><th align="center">Code</th><th align="center">Type</th><th align="center">Array?</th></tr></thead><tbody><tr><td>preference</td><td align="center">7</td><td align="center">uint8</td><td align="center">false</td></tr><tr><td>vendor-opts</td><td align="center">17</td><td align="center">uint32</td><td align="center">false</td></tr><tr><td>sip-server-dns</td><td align="center">21</td><td align="center">fqdn</td><td align="center">true</td></tr><tr><td>sip-server-addr</td><td align="center">22</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>dns-servers</td><td align="center">23</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>domain-search</td><td align="center">24</td><td align="center">fqdn</td><td align="center">true</td></tr><tr><td>nis-servers</td><td align="center">27</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>nisp-servers</td><td align="center">28</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>nis-domain-name</td><td align="center">29</td><td align="center">fqdn</td><td align="center">true</td></tr><tr><td>nisp-domain-name</td><td align="center">30</td><td align="center">fqdn</td><td align="center">true</td></tr><tr><td>sntp-servers</td><td align="center">31</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>information-refresh-time</td><td align="center">32</td><td align="center">uint32</td><td align="center">false</td></tr><tr><td>bcmcs-server-dns</td><td align="center">33</td><td align="center">fqdn</td><td align="center">true</td></tr><tr><td>bcmcs-server-addr</td><td align="center">34</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>geoconf-civic</td><td align="center">36</td><td align="center">record (uint8, uint16, binary)</td><td align="center">false</td></tr><tr><td>remote-id</td><td align="center">37</td><td align="center">record (uint32, binary)</td><td align="center">false</td></tr><tr><td>subscriber-id</td><td align="center">38</td><td align="center">binary</td><td align="center">false</td></tr><tr><td>client-fqdn</td><td align="center">39</td><td align="center">record (uint8, fqdn)</td><td align="center">false</td></tr><tr><td>pana-agent</td><td align="center">40</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>new-posix-timezone</td><td align="center">41</td><td align="center">string</td><td align="center">false</td></tr><tr><td>new-tzdb-timezone</td><td align="center">42</td><td align="center">string</td><td align="center">false</td></tr><tr><td>ero</td><td align="center">43</td><td align="center">uint16</td><td align="center">true</td></tr><tr><td>lq-query</td><td align="center">44</td><td align="center">record (uint8, ipv6-address)</td><td align="center">false</td></tr><tr><td>client-data</td><td align="center">45</td><td align="center">empty</td><td align="center">false</td></tr><tr><td>clt-time</td><td align="center">46</td><td align="center">uint32</td><td align="center">false</td></tr><tr><td>lq-relay-data</td><td align="center">47</td><td align="center">record (ipv6-address, binary)</td><td align="center">false</td></tr><tr><td>lq-client-link</td><td align="center">48</td><td align="center">ipv6-address</td><td align="center">true</td></tr><tr><td>bootfile-url</td><td align="center">59</td><td align="center">string</td><td align="center">false</td></tr><tr><td>bootfile-param</td><td align="center">60</td><td align="center">binary</td><td align="center">false</td></tr><tr><td>client-arch-type</td><td align="center">61</td><td align="center">uint16</td><td align="center">true</td></tr><tr><td>nii</td><td align="center">62</td><td align="center">record (uint8, uint8, uint8)</td><td align="center">false</td></tr><tr><td>erp-local-domain-name</td><td align="center">65</td><td align="center">fqdn</td><td align="center">false</td></tr><tr><td>rsoo</td><td align="center">66</td><td align="center">empty</td><td align="center">false</td></tr><tr><td>client-linklayer-addr</td><td align="center">79</td><td align="center">binary</td><td align="center">false</td></tr><tr><td>dhcp4o6-server-addr</td><td align="center">88</td><td align="center">ipv6-address</td><td align="center">true</td></tr></tbody></table></div></div><p><br class="table-break">
</p><p>
</p><div class="table"><a name="dhcp6-exp-options-list"></a><p class="title"><b>Table 8.2. List of experimental DHCPv6 options</b></p><div class="table-contents"><table summary="List of experimental DHCPv6 options" border="1"><colgroup><col class="name"><col align="center" class="code"><col align="center" class="type"><col align="center" class="array"></colgroup><thead><tr><th>Name</th><th align="center">Code</th><th align="center">Type</th><th align="center">Array?</th></tr></thead><tbody><tr><td>public-key</td><td align="center">701</td><td align="center">binary</td><td align="center">false</td></tr><tr><td>certificate</td><td align="center">702</td><td align="center">binary</td><td align="center">false</td></tr><tr><td>signature</td><td align="center">703</td><td align="center">record (uint8, uint8, binary)</td><td align="center">false</td></tr><tr><td>timestamp</td><td align="center">704</td><td align="center">binary</td><td align="center">false</td></tr></tbody></table></div></div><p><br class="table-break">
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-custom-options"></a>8.2.9. Custom DHCPv6 options</h3></div></div></div><p>It is also possible to define options other than the standard ones.
Assume that we want to define a new DHCPv6 option called "foo" which will have
code 100 and will convey a single unsigned 32 bit integer value. We can define
such an option by using the following commands:
</p><pre class="screen">
"Dhcp6": {
"option-def": [
{
<strong class="userinput"><code>"name": "foo",
"code": 100,
"type": "uint32",
"array": false,
"record-types": "",
"space": "dhcp6",
"encapsulate": ""</code></strong>
}, ...
],
...
}
</pre><p>
The "false" value of the "array" parameter determines that the option does
NOT comprise an array of "uint32" values but rather a single value. Two
other parameters have been left blank: "record-types" and "encapsulate".
The former specifies the comma separated list of option data fields if the
option comprises a record of data fields. The "record-fields" value should
be non-empty if the "type" is set to "record". Otherwise it must be left
blank. The latter parameter specifies the name of the option space being
encapsulated by the particular option. If the particular option does not
encapsulate any option space it should be left blank. Note that the above
set of comments define the format of the new option and do not set its
values.
</p><p>The <span class="command"><strong>name</strong></span>, <span class="command"><strong>code</strong></span> and
<span class="command"><strong>type</strong></span> parameters are required, all others are
optional. The <span class="command"><strong>array</strong></span> default value is
<span class="command"><strong>false</strong></span>. The <span class="command"><strong>record-types</strong></span>
and <span class="command"><strong>encapsulate</strong></span> default values are blank
(i.e. ""). The default <span class="command"><strong>space</strong></span> is "dhcp6".
</p><p>Once the new option format is defined, its value is set
in the same way as for a standard option. For example the following
commands set a global value that applies to all subnets.
</p><pre class="screen">
"Dhcp6": {
"option-data": [
{
<strong class="userinput"><code>"name": "foo",
"code": 100,
"space": "dhcp6",
"csv-format": true,
"data": "12345"</code></strong>
}, ...
],
...
}
</pre><p>
</p><p>New options can take more complex forms than simple use of
primitives (uint8, string, ipv6-address etc): it is possible to
define an option comprising a number of existing primitives.
</p><p>
Assume we want to define a new option that will consist of an IPv6
address, followed by an unsigned 16 bit integer, followed by a
boolean value, followed by a text string. Such an option could
be defined in the following way:
</p><pre class="screen">
"Dhcp6": {
"option-def": [
{
<strong class="userinput"><code>"name": "bar",
"code": 101,
"space": "dhcp6",
"type": "record",
"array": false,
"record-types": "ipv6-address, uint16, boolean, string",
"encapsulate": ""</code></strong>
}, ...
],
...
}
</pre><p>
The "type" is set to "record" to indicate that the option contains
multiple values of different types. These types are given as a comma-separated
list in the "record-types" field and should be those listed in <a class="xref" href="#dhcp-types" title="Table 7.3. List of standard DHCP option types">Table 7.3, “List of standard DHCP option types”</a>.
</p><p>
The values of the option are set as follows:
</p><pre class="screen">
"Dhcp6": {
"option-data": [
{
<strong class="userinput"><code>"name": "bar",
"space": "dhcp6",
"code": 101,
"csv-format": true,
"data": "2001:db8:1::10, 123, false, Hello World"</code></strong>
}
],
...
}</pre><p>
<span class="command"><strong>csv-format</strong></span> is set <span class="command"><strong>true</strong></span> to indicate
that the <span class="command"><strong>data</strong></span> field comprises a command-separated list
of values. The values in the "data" must correspond to the types set in
the "record-types" field of the option definition.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>In the general case, boolean values are specified as <span class="command"><strong>true</strong></span> or
<span class="command"><strong>false</strong></span>, without quotes. Some specific boolean parameters may
accept also <span class="command"><strong>"true"</strong></span>, <span class="command"><strong>"false"</strong></span>,
<span class="command"><strong>0</strong></span>, <span class="command"><strong>1</strong></span>, <span class="command"><strong>"0"</strong></span> and
<span class="command"><strong>"1"</strong></span>. Future Kea versions will accept all those values
for all boolean parameters.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-vendor-opts"></a>8.2.10. DHCPv6 vendor specific options</h3></div></div></div><p>
Currently there are two option spaces defined for the DHCPv6
daemon: "dhcp6" (for top level DHCPv6 options) and "vendor-opts-space",
which is empty by default, but options can be defined in it.
Those options will be carried in the Vendor-specific
Information option (code 17). The following examples show how to
define an option "foo" with code 1 that consists of an IPv6 address,
an unsigned 16 bit integer and a string. The "foo" option is
conveyed in a Vendor-specific Information option. This option
comprises a single uint32 value that is set to "12345".
The sub-option "foo" follows the data field holding this value.
</p><pre class="screen">
"Dhcp6": {
"option-def": [
{
<strong class="userinput"><code>"name": "foo",
"code": 1,
"space": "vendor-opts-space",
"type": "record",
"array": false,
"record-types": "ipv6-address, uint16, string",
"encapsulate": ""</code></strong>
}
],
...
}</pre><p>
(Note that the option space is set to <span class="command"><strong>vendor-opts-space</strong></span>.)
Once the option format is defined, the next step is to define actual values
for that option:
</p><pre class="screen">
"Dhcp6": {
"option-data": [
{
<strong class="userinput"><code>"name": "foo",
"space": "vendor-opts-space",
"data": "2001:db8:1::10, 123, Hello World"</code></strong>
},
...
],
...
}</pre><p>
We should also define a value (enterprise-number) for the
Vendor-specific Information option, that conveys our option "foo".
</p><pre class="screen">
"Dhcp6": {
"option-data": [
...,
{
<strong class="userinput"><code>"name": "vendor-opts",
"data": "12345"</code></strong>
}
],
...
}</pre><p>
Alternatively, the option can be specified using its code.
</p><pre class="screen">
"Dhcp6": {
"option-data": [
...,
{
<strong class="userinput"><code>"code": 17,
"data": "12345"</code></strong>
}
],
...
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-option-spaces"></a>8.2.11. Nested DHCPv6 options (custom option spaces)</h3></div></div></div><p>It is sometimes useful to define completely new option
spaces. This is useful if the user wants his new option to
convey sub-options that use a separate numbering scheme, for
example sub-options with codes 1 and 2. Those option codes
conflict with standard DHCPv6 options, so a separate option
space must be defined.
</p><p>Note that it is not required to create a new option space when
defining sub-options for a standard option because it is
created by default if the standard option is meant to convey
any sub-options (see <a class="xref" href="#dhcp6-vendor-opts" title="8.2.10. DHCPv6 vendor specific options">Section 8.2.10, “DHCPv6 vendor specific options”</a>).
</p><p>
Assume that we want to have a DHCPv6 option called "container"
with code 102 that conveys two sub-options with codes 1 and 2.
First we need to define the new sub-options:
</p><pre class="screen">
"Dhcp6": {
"option-def": [
{
<strong class="userinput"><code>"name": "subopt1",
"code": 1,
"space": "isc",
"type": "ipv6-address",
"record-types": "",
"array": false,
"encapsulate": ""</code></strong>
},
{
<strong class="userinput"><code>"name": "subopt2",
"code": 2,
"space": "isc",
"type": "string",
"record-types": "",
"array": false
"encapsulate": ""</code></strong>
}
],
...
}</pre><p>
Note that we have defined the options to belong to a new option space
(in this case, "isc").
</p><p>
The next step is to define a regular DHCPv6 option and specify that it
should include options from the isc option space:
</p><pre class="screen">
"Dhcp6": {
"option-def": [
...,
{
<strong class="userinput"><code>"name": "container",
"code": 102,
"space": "dhcp6",
"type": "empty",
"array": false,
"record-types": "",
"encapsulate": "isc"</code></strong>
}
],
...
}</pre><p>
The name of the option space in which the sub-options are defined is set in
the <span class="command"><strong>encapsulate</strong></span> field. The <span class="command"><strong>type</strong></span> field
is set to <span class="command"><strong>empty</strong></span> which limits this option to only carrying
data in sub-options.
</p><p>
Finally, we can set values for the new options:
</p><pre class="screen">
"Dhcp6": {
"option-data": [
{
<strong class="userinput"><code>"name": "subopt1",
"code": 1,
"space": "isc",
"data": "2001:db8::abcd"</code></strong>
},
}
<strong class="userinput"><code>"name": "subopt2",
"code": 2,
"space": "isc",
"data": "Hello world"</code></strong>
},
{
<strong class="userinput"><code>"name": "container",
"code": 102,
"space": "dhcp6"</code></strong>
}
],
...
}
</pre><p>
</p><p>Note that it is possible to create an option which carries some data
in addition to the sub-options defined in the encapsulated option space.
For example, if the "container" option from the previous example was
required to carry an uint16 value as well as the sub-options, the "type"
value would have to be set to "uint16" in the option definition. (Such an
option would then have the following data structure: DHCP header, uint16
value, sub-options.) The value specified with the "data" parameter — which
should be a valid integer enclosed in quotes, e.g. "123" — would then be
assigned to the uint16 field in the "container" option.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-option-data-defaults"></a>8.2.12. Unspecified parameters for DHCPv6 option configuration</h3></div></div></div><p>In many cases it is not required to specify all parameters for
an option configuration and the default values can be used. However, it is
important to understand the implications of not specifying some of them
as it may result in configuration errors. The list below explains
the behavior of the server when a particular parameter is not explicitly
specified:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>name</strong></span> - the server requires an option name or
option code to identify an option. If this parameter is unspecified, the
option code must be specified.
</li><li class="listitem"><span class="command"><strong>code</strong></span> - the server requires an option name or
option code to identify an option. This parameter may be left unspecified if
the <span class="command"><strong>name</strong></span> parameter is specified. However, this also
requires that the particular option has its definition (it is either a
standard option or an administrator created a definition for the option
using an 'option-def' structure), as the option definition associates an
option with a particular name. It is possible to configure an option
for which there is no definition (unspecified option format).
Configuration of such options requires the use of option code.
</li><li class="listitem"><span class="command"><strong>space</strong></span> - if the option space is unspecified it
will default to 'dhcp6' which is an option space holding DHCPv6 standard
options.
</li><li class="listitem"><span class="command"><strong>data</strong></span> - if the option data is unspecified it
defaults to an empty value. The empty value is mostly used for the
options which have no payload (boolean options), but it is legal to specify
empty values for some options which carry variable length data and which
spec allows for the length of 0. For such options, the data parameter
may be omitted in the configuration.</li><li class="listitem"><span class="command"><strong>csv-format</strong></span> - if this value is not specified
and the definition for the particular option exists, the server will assume
that the option data is specified as a list of comma separated values to be
assigned to individual fields of the DHCP option. If the definition
does not exist for this option, the server will assume that the data
parameter contains the option payload in the binary format (represented
as a string of hexadecimal digits). Note that not specifying this
parameter doesn't imply that it defaults to a fixed value, but
the configuration data interpretation also depends on the presence
of the option definition. An administrator must be aware if the
definition for the particular option exists when this parameter
is not specified. It is generally recommended to not specify this
parameter only for the options for which the definition exists, e.g.
standard options. Setting <span class="command"><strong>csv-format</strong></span> to an explicit
value will cause the server to strictly check the format of the option
data specified.
</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-config-subnets"></a>8.2.13. IPv6 Subnet Selection</h3></div></div></div><p>
The DHCPv6 server may receive requests from local (connected to the
same subnet as the server) and remote (connecting via relays) clients.
As the server may have many subnet configurations defined, it must select
an appropriate subnet for a given request.
</p><p>
The server can not assume which of the configured subnets are local. In IPv4
it is possible as there is a reasonable expectation that the
server will have a (global) IPv4 address configured on the interface,
and can use that information to detect whether a subnet is local or
not. That assumption is not true in IPv6, the DHCPv6 server must be able
to operate while only having link-local addresses. Therefore an optional
"interface" parameter is available within a subnet definition
to designate that a given subnet is local, i.e. reachable directly over
the specified interface. For example the server that is intended to serve
a local subnet over eth0 may be configured as follows:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"pools": [
{
"pool": "2001:db8:beef::/48"
}
],
<strong class="userinput"><code>"interface": "eth0"</code></strong>
}
],
...
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-rapid-commit"></a>8.2.14. Rapid Commit</h3></div></div></div><p>The Rapid Commit option, described in
<a class="ulink" href="http://tools.ietf.org/html/rfc3315" target="_top">RFC 3315</a>, is supported
by the Kea DHCPv6 server. However, support is disabled by default for
all subnets. It can be enabled for a particular subnet using the
<span class="command"><strong>rapid-commit</strong></span> parameter as shown below:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
<strong class="userinput"><code>"rapid-commit": true</code></strong>,
"pools": [
{
"pool": "2001:db8:beef::1-2001:db8:beef::10"
}
],
}
],
...
}
</pre><p>
</p><p>
This setting only affects the subnet for which the
<span class="command"><strong>rapid-commit</strong></span> is set to <span class="command"><strong>true</strong></span>.
For clients connected to other subnets, the server will ignore the
Rapid Commit option sent by the client and will follow the 4-way
exchange procedure, i.e. respond with the Advertise for the Solicit
containing Rapid Commit option.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-relays"></a>8.2.15. DHCPv6 Relays</h3></div></div></div><p>
A DHCPv6 server with multiple subnets defined must select the
appropriate subnet when it receives a request from a client. For clients
connected via relays, two mechanisms are used:
</p><p>
The first uses the linkaddr field in the RELAY_FORW message. The name
of this field is somewhat misleading in that it does not contain a link-layer
address: instead, it holds an address (typically a global address) that is
used to identify a link. The DHCPv6 server checks if the address belongs
to a defined subnet and, if it does, that subnet is selected for the client's
request.
</p><p>
The second mechanism is based on interface-id options. While forwarding a client's
message, relays may insert an interface-id option into the message that
identifies the interface on the relay that received the message. (Some
relays allow configuration of that parameter, but it is sometimes
hardcoded and may range from the very simple (e.g. "vlan100") to the very cryptic:
one example seen on real hardware was "ISAM144|299|ipv6|nt:vp:1:110"). The
server can use this information to select the appropriate subnet.
The information is also returned to the relay which then knows the
interface to use to transmit the response to the client. In order for
this to work successfully, the relay interface IDs must be unique within
the network and the server configuration must match those values.
</p><p>
When configuring the DHCPv6 server, it should be noted that two
similarly-named parameters can be configured for a subnet:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
"interface" defines which local network interface can be used
to access a given subnet.
</li><li class="listitem">
"interface-id" specifies the content of the interface-id option
used by relays to identify the interface on the relay to which
the response packet is sent.
</li></ul></div><p>
The two are mutually exclusive: a subnet cannot be both reachable locally
(direct traffic) and via relays (remote traffic). Specifying both is a
configuration error and the DHCPv6 server will refuse such a configuration.
</p><p>
To specify interface-id with value "vlan123", the following commands can
be used:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"pools": [
{
"pool": "2001:db8:beef::/48"
}
],
<strong class="userinput"><code>"interface-id": "vlan123"</code></strong>
}
],
...
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-rsoo"></a>8.2.16. Relay-Supplied Options</h3></div></div></div><p><a class="ulink" href="http://tools.ietf.org/html/rfc6422" target="_top">RFC 6422</a>
defines a mechanism called Relay-Supplied DHCP Options. In certain cases relay
agents are the only entities that may have specific information. They can
insert options when relaying messages from the client to the server. The
server will then do certain checks and copy those options to the response
that will be sent to the client.</p><p>There are certain conditions that must be met for the option to be
included. First, the server must not provide the option by itself. In
other words, if both relay and server provide an option, the server always
takes precedence. Second, the option must be RSOO-enabled. IANA maintains a
list of RSOO-enabled options <a class="ulink" href="http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml#options-relay-supplied" target="_top">here</a>.
However, there may be cases when system administrators want to echo other
options. Kea can be instructed to treat other options as RSOO-enabled.
For example, to mark options 110, 120 and 130 as RSOO-enabled, the following
syntax should be used:
</p><pre class="screen">
"Dhcp6": {
<strong class="userinput"><code>"relay-supplied-options": [ "110", "120", "130" ],</code></strong>
...
}
</pre><p>
</p><p>As of March 2015, only option 65 is RSOO-enabled by IANA. This
option will always be treated as such and there's no need to explicitly
mark it. Also, when enabling standard options, it is possible to use their
names, rather than option code, e.g. (e.g. use
<span class="command"><strong>dns-servers</strong></span> instead of <span class="command"><strong>23</strong></span>). See
<a class="xref" href="#dhcp6-std-options-list" title="Table 8.1. List of standard DHCPv6 options">Table 8.1, “List of standard DHCPv6 options”</a> for the names. In certain cases
it could also work for custom options, but due to the nature of the parser
code this may be unreliable and should be avoided.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-client-classifier"></a>8.2.17. Client Classification in DHCPv6</h3></div></div></div><p>
The DHCPv6 server includes support for client classification. At the
current time the capabilities of the classification process are limited
but it is expected they will be expanded in the future. For a deeper
discussion of the classification process see <a class="xref" href="#classify" title="Chapter 12. Client Classification">Chapter 12, <i>Client Classification</i></a>.
</p><p>
In certain cases it is useful to differentiate between different types
of clients and treat them accordingly. It is envisaged that client
classification will be used for changing the behavior of almost any part of
the DHCP message processing, including the assignment of leases from different
pools, the assignment of different options (or different values of the same
options) etc. In the current release of the software however, there are
only two mechanisms that take advantage of client classification:
subnet selection and assignment of different options.
</p><p>
Kea can be instructed to limit access to given subnets based on class information.
This is particularly useful for cases where two types of devices share the
same link and are expected to be served from two different subnets. The
primary use case for such a scenario is cable networks. There are two
classes of devices: the cable modem itself, which should be handed a lease
from subnet A and all other devices behind the modem that should get a lease
from subnet B. That segregation is essential to prevent overly curious
users from playing with their cable modems. For details on how to set up
class restrictions on subnets, see <a class="xref" href="#classification-subnets" title="12.5. Configuring Subnets With Class Information">Section 12.5, “Configuring Subnets With Class Information”</a>.
</p><p>
The process of doing classification is conducted in three steps. The first step
is to assess an incoming packet and assign it to zero or more classes. The
second step is to choose a subnet, possibly based on the class information.
The third step is to assign options again possibly based on the class
information.
</p><p>
There are two methods of doing classification. The first is automatic and relies
on examining the values in the vendor class options. Information from these
options is extracted and a class name is constructed from it and added to
the class list for the packet. The second allows you to specify an expression
that is evaluated for each packet. If the result is true the packet is
a member of the class.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Care should be taken with client classification as it is easy for
clients that do not meet class criteria to be denied any service altogether.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp56625104"></a>8.2.17.1. Defining and Using Custom Classes</h4></div></div></div><p>
The following example shows how to configure a class using an expression
and a subnet making use of that class. This configuration defines the
class named "Client_enterprise". It is comprised
of all clients who's client identifiers start with the given hex string (which
would indicate a DUID based on an enterprise id of 0xAABBCCDD).
They will be given an address from 2001:db8:1::0 to 2001:db8:1::FFFF and
2001:db8:0::1 and 2001:db8:2::1 for their domain name servers. For a deeper
discussion of the classification process see <a class="xref" href="#classify" title="Chapter 12. Client Classification">Chapter 12, <i>Client Classification</i></a>.
</p><pre class="screen">
"Dhcp6": {
"client-classes": [
{<strong class="userinput"><code>
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]</code></strong>
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
<strong class="userinput"><code>"client-class": "Client_enterprise"</code></strong>
}
],
...
}</pre><p>
</p><p>
This example shows a configuration using an automatically generated
"VENDOR_CLASS_" class. The Administrator of the network has
decided that addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are
going to be managed by the Dhcp6 server and only clients belonging to the
eRouter1.0 client class are allowed to use that pool.
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::-2001:db8:1::ffff"
}
],
<strong class="userinput"><code>"client-class": "VENDOR_CLASS_eRouter1.0"</code></strong>
}
],
...
}
</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dhcp6-ddns-config"></a>8.2.18. Configuring DHCPv6 for DDNS</h3></div></div></div><p>
As mentioned earlier, kea-dhcp6 can be configured to generate requests to
the DHCP-DDNS server (referred to here as "D2") to update
DNS entries. These requests are known as NameChangeRequests or NCRs.
Each NCR contains the following information:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Whether it is a request to add (update) or remove DNS entries
</p></li><li class="listitem"><p>
Whether the change requests forward DNS updates (AAAA records), reverse
DNS updates (PTR records), or both.
</p></li><li class="listitem"><p>
The FQDN, lease address, and DHCID
</p></li></ol></div><p>
The parameters controlling the generation of NCRs for submission to D2
are contained in the "dhcp-ddns" section of kea-dhcp6
configuration. The mandatory parameters for the DHCP DDNS configuration
are <span class="command"><strong>enable-updates</strong></span> which is unconditionally
required, and <span class="command"><strong>qualifying-suffix</strong></span> which has no
default value and is required when <span class="command"><strong>enable-updates</strong></span>
is set to <span class="command"><strong>true</strong></span>.
The two (disabled and enabled) minimal DHCP DDNS configurations are:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"enable-updates": false</code></strong>
},
...
}
</pre><p>
and for example:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"enable-updates": true,
"qualifying-suffix": "example."</code></strong>
},
...
}
</pre><p>
The default values for the "dhcp-ddns" section are as follows:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>"server-ip": "127.0.0.1"</strong></span>
</li><li class="listitem">
<span class="command"><strong>"server-port": 53001</strong></span>
</li><li class="listitem">
<span class="command"><strong>"sender-ip": ""</strong></span>
</li><li class="listitem">
<span class="command"><strong>"sender-port": 0</strong></span>
</li><li class="listitem">
<span class="command"><strong>"max-queue-size": 1024</strong></span>
</li><li class="listitem">
<span class="command"><strong>"ncr-protocol": "UDP"</strong></span>
</li><li class="listitem">
<span class="command"><strong>"ncr-format": "JSON"</strong></span>
</li><li class="listitem">
<span class="command"><strong>"override-no-update": false</strong></span>
</li><li class="listitem">
<span class="command"><strong>"override-client-update": false</strong></span>
</li><li class="listitem">
<span class="command"><strong>"replace-client-name": false</strong></span>
</li><li class="listitem">
<span class="command"><strong>"generated-prefix": "myhost"</strong></span>
</li></ul></div><p>
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dhcpv6-d2-io-config"></a>8.2.18.1. DHCP-DDNS Server Connectivity</h4></div></div></div><p>
In order for NCRs to reach the D2 server, kea-dhcp6 must be able
to communicate with it. kea-dhcp6 uses the following configuration
parameters to control how it communications with D2:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>enable-updates</strong></span> - determines whether or not kea-dhcp6 will
generate NCRs. If missing, this value is assumed to be false hence DDNS updates
are disabled. To enable DDNS updates set this value to true:
</li><li class="listitem">
<span class="command"><strong>server-ip</strong></span> - IP address on which D2 listens for requests. The default is
the local loopback interface at address 127.0.0.1. You may specify
either an IPv4 or IPv6 address.
</li><li class="listitem">
<span class="command"><strong>server-port</strong></span> - port on which D2 listens for requests. The default value
is 53001.
</li><li class="listitem">
<span class="command"><strong>sender-ip</strong></span> - IP address which kea-dhcp6 should use to send requests to D2.
The default value is blank which instructs kea-dhcp6 to select a suitable
address.
</li><li class="listitem">
<span class="command"><strong>sender-port</strong></span> - port which kea-dhcp6 should use to send requests to D2. The
default value of 0 instructs kea-dhcp6 to select a suitable port.
</li><li class="listitem">
<span class="command"><strong>max-queue-size</strong></span> - maximum number of requests allowed to queue waiting to
be sent to D2. This value guards against requests accumulating
uncontrollably if they are being generated faster than they can be
delivered. If the number of requests queued for transmission reaches
this value, DDNS updating will be turned off until the queue backlog has
been sufficiently reduced. The intent is to allow kea-dhcp6 to
continue lease operations. The default value is 1024.
</li><li class="listitem">
<span class="command"><strong>ncr-protocol</strong></span> - Socket protocol use when sending requests to D2. Currently
only UDP is supported. TCP may be available in an upcoming release.
</li><li class="listitem">
<span class="command"><strong>ncr-format</strong></span> - Packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be available
in future releases.
</li></ul></div><p>
By default, kea-dhcp-ddns is assumed to running on the same machine as kea-dhcp6, and
all of the default values mentioned above should be sufficient.
If, however, D2 has been configured to listen on a different address or
port, these values must altered accordingly. For example, if D2 has been
configured to listen on 2001:db8::5 port 900, the following commands
would be required:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"server-ip": "2001:db8::5",
"server-port": 900</code></strong>,
...
},
...
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dhcpv6-d2-rules-config"></a>8.2.18.2. When does kea-dhcp6 generate DDNS request</h4></div></div></div><p>kea-dhcp6 follows the behavior prescribed for DHCP servers in
<a class="ulink" href="http://tools.ietf.org/html/rfc4704" target="_top">RFC 4704</a>.
It is important to keep in mind that kea-dhcp6 provides the initial
decision making of when and what to update and forwards that
information to D2 in the form of NCRs. Carrying out the actual
DNS updates and dealing with such things as conflict resolution
are the purview of D2 (<a class="xref" href="#dhcp-ddns-server" title="Chapter 10. The DHCP-DDNS Server">Chapter 10, <i>The DHCP-DDNS Server</i></a>).</p><p>
This section describes when kea-dhcp6 will generate NCRs and the
configuration parameters that can be used to influence this decision.
It assumes that the "enable-updates" parameter is true.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Currently the interface between kea-dhcp6 and D2 only supports requests
which update DNS entries for a single IP address. If a lease grants
more than one address, kea-dhcp6 will create the DDNS update request for
only the first of these addresses. Support for multiple address
mappings may be provided in a future release.
</p></div><p>
In general, kea-dhcp6 will generate DDNS update requests when:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
A new lease is granted in response to a DHCP REQUEST
</p></li><li class="listitem"><p>
An existing lease is renewed but the FQDN associated with it has
changed.
</p></li><li class="listitem"><p>
An existing lease is released in response to a DHCP RELEASE
</p></li></ol></div><p>
In the second case, lease renewal, two DDNS requests will be issued: one
request to remove entries for the previous FQDN and a second request to
add entries for the new FQDN. In the last case, a lease release, a
single DDNS request to remove its entries will be made. The decision
making involved when granting a new lease is more involved and is
discussed next.
</p><p>
kea-dhcp6 will generate a DDNS update request only if the DHCP REQUEST
contains the FQDN option (code 39). By default kea-dhcp6 will
respect the FQDN N and S flags specified by the client as shown in the
following table:
</p><div class="table"><a name="dhcp6-fqdn-flag-table"></a><p class="title"><b>Table 8.3. Default FQDN Flag Behavior</b></p><div class="table-contents"><table summary="Default FQDN Flag Behavior" border="1"><colgroup><col align="left" class="cflags"><col align="left" class="meaning"><col align="left" class="response"><col align="left" class="sflags"></colgroup><thead><tr><th align="left">Client Flags:N-S</th><th align="left">Client Intent</th><th align="left">Server Response</th><th align="left">Server Flags:N-S-O</th></tr></thead><tbody><tr><td align="left">0-0</td><td align="left">
Client wants to do forward updates, server should do reverse updates
</td><td align="left">Server generates reverse-only request</td><td align="left">1-0-0</td></tr><tr><td align="left">0-1</td><td align="left">Server should do both forward and reverse updates</td><td align="left">Server generates request to update both directions</td><td align="left">0-1-0</td></tr><tr><td align="left">1-0</td><td align="left">Client wants no updates done</td><td align="left">Server does not generate a request</td><td align="left">1-0-0</td></tr></tbody></table></div></div><br class="table-break"><p>
The first row in the table above represents "client delegation". Here
the DHCP client states that it intends to do the forward DNS updates and
the server should do the reverse updates. By default, kea-dhcp6 will honor
the client's wishes and generate a DDNS request to D2 to update only
reverse DNS data. The parameter, "override-client-update", can be used
to instruct the server to override client delegation requests. When
this parameter is true, kea-dhcp6 will disregard requests for client
delegation and generate a DDNS request to update both forward and
reverse DNS data. In this case, the N-S-O flags in the server's
response to the client will be 0-1-1 respectively.
</p><p>
(Note that the flag combination N=1, S=1 is prohibited according to
RFC 4702. If such a combination is received from the client, the packet
will be dropped by kea-dhcp6.)
</p><p>
To override client delegation, issue the following commands:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"override-client-update": true</code></strong>,
...
},
...
}
</pre><p>
The third row in the table above describes the case in which the client
requests that no DNS updates be done. The parameter, "override-no-update",
can be used to instruct the server to disregard the client's wishes. When
this parameter is true, kea-dhcp6 will generate DDNS update requests to
kea-dhcp-ddns even if the client requests no updates be done. The N-S-O
flags in the server's response to the client will be 0-1-1.
</p><p>
To override client delegation, issue the following commands:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"override-no-update": true</code></strong>,
...
},
...
}
</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dhcpv6-fqdn-name-generation"></a>8.2.18.3. kea-dhcp6 name generation for DDNS update requests</h4></div></div></div><p>Each NameChangeRequest must of course include the fully qualified domain
name whose DNS entries are to be affected. kea-dhcp6 can be configured to
supply a portion or all of that name based upon what it receives from
the client in the DHCP REQUEST.</p><p>The rules for determining the FQDN option are as follows:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
If configured to do so ignore the REQUEST contents and generate a
FQDN using a configurable prefix and suffix.
</p></li><li class="listitem"><p>
Otherwise, using the domain name value from the client FQDN option as
the candidate name:
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>
If the candidate name is a fully qualified domain name then use it.
</p></li><li class="listitem"><p>
If the candidate name is a partial (i.e. unqualified) name then
add a configurable suffix to the name and use the result as the FQDN.
</p></li><li class="listitem"><p>
If the candidate name is a empty then generate a FQDN using a
configurable prefix and suffix.
</p></li></ol></div><p>
</p></li></ol></div><p>
To instruct kea-dhcp6 to always generate a FQDN, set the parameter
"replace-client-name" to true:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"replace-client-name": true</code></strong>,
...
},
...
}
</pre><p>
The prefix used when generating a FQDN is specified by the
"generated-prefix" parameter. The default value is "myhost". To alter
its value, simply set it to the desired string:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"generated-prefix": "another.host"</code></strong>,
...
},
...
}
</pre><p>
The suffix used when generating a FQDN or when qualifying a
partial name is specified by
the <span class="command"><strong>qualifying-suffix</strong></span> parameter. This
parameter has no default value, thus it is mandatory when
DDNS updates are enabled.
To set its value simply set it to the desired string:
</p><pre class="screen">
"Dhcp6": {
"dhcp-ddns": {
<strong class="userinput"><code>"qualifying-suffix": "foo.example.org"</code></strong>,
...
},
...
}
</pre></div><p>
When qualifying a partial name, kea-dhcp6 will construct a name with the
format:
</p><p>
[candidate-name].[qualifying-suffix].
</p><p>
where candidate-name is the partial name supplied in the REQUEST.
For example, if FQDN domain name value was "some-computer" and
qualifying-suffix "example.com", the generated FQDN would be:
</p><p>
some-computer.example.com.
</p><p>
When generating the entire name, kea-dhcp6 will construct name of the
format:
</p><p>
[generated-prefix]-[address-text].[qualifying-suffix].
</p><p>
where address-text is simply the lease IP address converted to a
hyphenated string. For example, if lease address is 3001:1::70E,
the qualifying suffix "example.com", and the default value is used for
<span class="command"><strong>generated-prefix</strong></span>, the generated FQDN would be:
</p><p>
myhost-3001-1--70E.example.com.
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="host-reservation-v6"></a>8.3. Host reservation in DHCPv6</h2></div></div></div><p>There are many cases where it is useful to provide a configuration on
a per host basis. The most obvious one is to reserve specific, static IPv6
address or/and prefix for exclusive use by a given client (host) ‐ returning
client will get the same address or/and prefix every time and other clients will
never get that address. Note that there may be cases when the
new reservation has been made for the client for the address or prefix being
currently in use by another client. We call this situation a "conflict". The
conflicts get resolved automatically over time as described in the subsequent
sections. Once conflict is resolved, the client will keep receiving the reserved
configuration when it renews.</p><p>Another example when the host reservations are applicable is when a host
that has specific requirements, e.g. a printer that needs additional DHCP options
or a cable modem needs specific parameters. Yet another possible use case for
host reservation is to define unique names for hosts. Although not all of
the presented use cases are implemented yet, Kea software will support them
in the near future.</p><p>Hosts reservations are defined as parameters for each subnet. Each host
can be identified by either DUID or its hardware/MAC address. See
<a class="xref" href="#mac-in-dhcpv6" title="8.9. MAC/Hardware addresses in DHCPv6">Section 8.9, “MAC/Hardware addresses in DHCPv6”</a> for details. There is an optional
<span class="command"><strong>reservations</strong></span> array in the
<span class="command"><strong>Subnet6</strong></span> structure. Each element in that array
is a structure, that holds information about a single host. In
particular, such a structure has to have an identifier that
uniquely identifies a host. In DHCPv6 context, such an identifier
is a hardware (MAC) address or a DUID. Also, either one or more
addresses or prefixes should be specified. It is possible to
specify a hostname. Additional capabilities are planned.</p><p>The following example shows how to reserve addresses and prefixes
for specific hosts:
</p><pre class="screen">
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"pd-pools": [
{
"prefix": "2001:db8:1:8000::",
"prefix-len": 56,
"delegated-len": 64
}
],
<strong class="userinput"><code>"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
},
{
"hw-address": "00:01:02:03:04:05",
"ip-addresses": [ "2001:db8:1::101" ]
},
{
"duid": "01:02:03:04:05:06:07:08:09:0A",
"ip-addresses": [ "2001:db8:1::102" ],
"prefixes": [ "2001:db8:2:abcd::/64" ],
"hostname": "foo.example.com"
}
]</code></strong>
}
]
</pre><p>
This example makes 3 reservations. The first one reserves 2001:db8:1::100 address
for the client using DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The second one
also reserves an address, but does so using MAC or hardware address, rather than
DUID. The third example is most advanced. It reserves an address, a prefix and
a hostname at the same time.
</p><p>Note that DHCPv6 allows for a single client to lease multiple addresses
and multiple prefixes at the same time. In the upcoming Kea releases, it will
be possible to have multiple addresses and prefixes reserved for a single
host. Therefore <span class="command"><strong>ip-addresses</strong></span> and <span class="command"><strong>prefixes</strong></span>
are plural and are actually arrays. As of 0.9.1 having more than one IPv6
address or prefix is only partially supported.</p><p>Making a reservation for a mobile host that may visit multiple subnets
requires a separate host definition in each subnet it is expected to visit.
It is not allowed to define multiple host definitions with the same hardware
address in a single subnet. It is a valid configuration, if such definitions
are specified in different subnets, though. The reservation for a given host
should include only one identifier, either DUID or hardware address. Defining
both for the same host is considered a configuration error, but as of 0.9.1
beta, it is not rejected.
</p><p>Adding host reservation incurs a performance penalty. In principle,
when the server that does not support host reservation responds to a query,
it needs to check whether there is a lease for a given address being
considered for allocation or renewal. The server that also supports host
reservation, has to perform additional checks: not only if the address is
currently used (if there is a lease for it), but also whether the address
could be used by someone else (if there is a reservation for it). That
additional check incurs performance penalty.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation6-types"></a>8.3.1. Address/prefix reservation types</h3></div></div></div><p>In a typical scenario there's an IPv6 subnet defined with a certain
part of it dedicated for dynamic address allocation by the DHCPv6
server. There may be an additional address space defined for prefix
delegation. Those dynamic parts are referred to as dynamic pools, address
and prefix pools or simply pools. In principle, the host reservation can
reserve any address or prefix that belongs to the subnet. The reservations
that specify an address that belongs to configured pools are called
<span class="command"><strong>in-pool reservations</strong></span>. In contrast, those that do not
belong to dynamic pools are called <span class="command"><strong>out-of-pool
reservations</strong></span>. There is no formal difference in the reservation
syntax. As of 0.9.1, both reservation types are handled
uniformly. However, upcoming releases may offer improved performance if
there are only out-of-pool reservations as the server will be able to skip
reservation checks when dealing with existing leases. Therefore, system
administrators are encouraged to use out-of-pool reservations, if
possible.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation6-conflict"></a>8.3.2. Conflicts in DHCPv6 reservations</h3></div></div></div><p>As reservations and lease information are stored in different places,
conflicts may arise. Consider the following series of events. The server
has configured the dynamic pool of addresses from the range of 2001:db8::10
to 2001:db8::20. Host A requests an address and gets 2001:db8::10. Now the
system administrator decides to reserve an address for host B. He decides
to reserve 2001:db8::10 for that purpose. In general, reserving an address
that is currently assigned to someone else is not recommended, but there
are valid use cases where such an operation is warranted.</p><p>The server now has a conflict to resolve. Let's analyze the
situation here. If host B boots up and request an address, the server is
not able to assign the reserved address 2001:db8::10. A naive approach
would to be immediately remove the lease for host A and create a new one
for host B. That would not solve the problem, though, because as soon as
host B get the address, it will detect that the address is already in use
by someone else (host A) and would send Decline. Therefore in this
situation, the server has to temporarily assign a different address from the
dynamic pool (not matching what has been reserved) to host B.</p><p>When the host A renews its address, the server will discover that
the address being renewed is now reserved for someone else (host
B). Therefore the server will remove the lease for 2001:db8::10 and select
a new address and will create a new lease for it. It will send two
addresses in its response: the old address with lifetimes set to 0 to
explicitly indicate that it is no longer valid and a new address with
non-zero lifetimes. When the host B renews its temporarily assigned
address, the server will detect that the existing lease does not match
reservation, so it will release the current address host B has and will
create a new lease matching the reservation. Similar as before, the server
will send two addresses: the temporarily assigned one with zeroed
lifetimes, and the new one that matches reservation with proper lifetimes
set.</p><p>This recovery will succeed, even if other hosts will attempt to get
the reserved address. Had the host C requested address 2001:db8::10 after
the reservation was made, the server will propose a different address.</p><p>This recovery mechanism allows the server to fully recover from a
case where reservations conflict with existing leases. This procedure
takes time and will roughly take as long as renew-timer value specified.
The best way to avoid such recovery is to not define new reservations that
conflict with existing leases. Another recommendation is to use
out-of-pool reservations. If the reserved address does not belong to a
pool, there is no way that other clients could get this address (note that
having multiple reservations for the same address is not allowed).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation6-hostname"></a>8.3.3. Reserving a hostname</h3></div></div></div><p>When the reservation for the client includes the <span class="command"><strong>hostname
</strong></span>, the server will assign this hostname to the client and send
it back in the Client FQDN, if the client sent the FQDN option to the
server. The reserved hostname always takes precedence over the hostname
supplied by the client (via the FQDN option) or the autogenerated
(from the IPv6 address) hostname.</p><p>The server qualifies the reserved hostname with the value
of the <span class="command"><strong>qualifying-suffix</strong></span> parameter. For example, the
following subnet configuration:
</p><pre class="screen">
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
"hostname": "alice-laptop"
}
]
}
],
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example.isc.org."
}
</pre><p>
will result in assigning the "alice-laptop.example.isc.org." hostname to the
client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the <span class="command"><strong>qualifying-suffix
</strong></span> is not specified, the default (empty) value will be used, and
in this case the value specified as a <span class="command"><strong>hostname</strong></span> will
be treated as fully qualified name. Thus, by leaving the
<span class="command"><strong>qualifying-suffix</strong></span> empty it is possible to qualify
hostnames for the different clients with different domain names:
</p><pre class="screen">
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
"hostname": "mark-desktop.example.org."
}
]
}
],
"dhcp-ddns": {
"enable-updates": true,
}
</pre><p>
will result in assigning the "mark-desktop.example.org." hostname to the
client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E".
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation6-options"></a>8.3.4. Reserving specific options</h3></div></div></div><p>Currently it is not possible to specify options in host
reservation. Such a feature will be added in the upcoming Kea
releases.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="reservation6-mode"></a>8.3.5. Fine Tuning IPv6 Host Reservation</h3></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><span class="command"><strong>reservation-mode</strong></span> in the DHCPv6 server is
implemented in Kea 0.9.1 beta, but has not been tested and is
considered experimental.</p></div><p>Host reservation capability introduces additional restrictions for the
allocation engine during lease selection and renewal. In particular, three
major checks are necessary. First, when selecting a new lease, it is not
sufficient for a candidate lease to be not used by another DHCP client. It
also must not be reserved for another client. Second, when renewing a lease,
additional check must be performed whether the address being renewed is not
reserved for another client. Finally, when a host renews an address or a
prefix, the server has to check whether there's a reservation for this host,
so the existing (dynamically allocated) address should be revoked and the
reserved one be used instead.</p><p>Some of those checks may be unnecessary in certain deployments. Not
performing them may improve performance. The Kea server provides the
<span class="command"><strong>reservation-mode</strong></span> configuration parameter to select the
types of reservations allowed for the particular subnet. Each reservation
type has different constraints for the checks to be performed by the
server when allocating or renewing a lease for the client.
Allowed values are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> <span class="command"><strong>all</strong></span> - enables all host reservation
types. This is the default value. This setting is the safest and the most
flexible. It allows in-pool and out-of-pool reservations. As all checks
are conducted, it is also the slowest.
</li><li class="listitem"> <span class="command"><strong>out-of-pool</strong></span> - allows only out of
pool host reservations. With this setting in place, the server may assume
that all host reservations are for addresses that do not belong to the
dynamic pool. Therefore it can skip the reservation checks when dealing
with in-pool addresses, thus improving performance. Do not use this mode
if any of your reservations use in-pool address. Caution is advised when
using this setting. Kea 0.9.1 does not sanity check the reservations against
<span class="command"><strong>reservation-mode</strong></span>. Misconfiguration may cause problems.
</li><li class="listitem">
<span class="command"><strong>disabled</strong></span> - host reservation support is disabled. As there
are no reservations, the server will skip all checks. Any reservations defined
will be completely ignored. As the checks are skipped, the server may
operate faster in this mode.
</li></ul></div><p>
</p><p>
An example configuration that disables reservation looks like follows:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
<strong class="userinput"><code>"reservation-mode": "disabled"</code></strong>,
...
}
]
}
</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-serverid"></a>8.4. Server Identifier in DHCPv6</h2></div></div></div><p>The DHCPv6 protocol uses a "server identifier" (also known
as a DUID) for clients to be able to discriminate between several
servers present on the same link.
<a class="ulink" href="http://tools.ietf.org/html/rfc3315" target="_top">RFC 3315</a>
defines three DUID types: DUID-LLT, DUID-EN and DUID-LL.
<a class="ulink" href="http://tools.ietf.org/html/rfc6355" target="_top">RFC 6355</a>
also defines DUID-UUID. Future specifications may introduce new
DUID types.</p><p>Kea DHCPv6 server generates a server identifier once, upon
the first startup, and stores it in a file. This identifier isn't
modified across restarts of the server (stable identifier).</p><p>Kea follows recommendation from
<a class="ulink" href="http://tools.ietf.org/html/rfc3315" target="_top">RFC 3315</a>
to use DUID-LLT as a default server identifier. However, we have
received reports that some deployments require different DUID
types, and there is a need to administratively select both DUID
type and/or its contents.</p><p>The server identifier can be configured using parameters
within the <span class="command"><strong>server-id</strong></span> map element in the global
scope of the Kea configuration file. The following example
demonstrates how to select DUID-EN as a server identifier:
</p><pre class="screen">
"Dhcp6": {
"server-id": {
"type": "EN"
},
...
}
</pre><p>
</p><p>Currently supported values for <span class="command"><strong>type</strong></span>
parameter are: "LLT", "EN" and "LL", for DUID-LLT, DUID-EN and
DUID-LL respectively.</p><p>When a new DUID type is selected the server will generate its
value and replace any existing DUID in the file. The server will
use the new server identifier in all future interactions with the
clients.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>If the new server identifier is created after some clients
have obtained their leases, the clients using old identifier will not
be able to renew the leases. The server will ignore messages
containing the old server identifier. Clients will continue sending
Renew until they transition to rebinding state. In this state they
will start sending Rebind messages to multicast address and without
a server identifier. The server will respond to the Rebind messages
with a new server identifier and the clients will associate the
new server identifier with their leases. Although the clients will
be able to keep their leases and will eventually learn the new server
identifier, this will be at the cost of increased number of renewals
and multicast traffic due to a need to rebind. Therefore it is
recommended to avoid modification of the server identifier type
and its value if the server has already assigned leases and these
leases are still valid.</p></div><p>There are cases when an administrator needs to explicitly
specify a DUID value, rather than allow the server to generate it.
The following example demonstrates how to explicitly set all
components of a DUID-LLT.
</p><pre class="screen">
"Dhcp6": {
"server-id": {
"type": "LLT",
"htype": 8,
"identifier": "A65DC7410F05",
"time": 2518920166
},
...
}
</pre><p>
where:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>htype</strong></span> is a 16-bit unsigned value
specifying hardware type,</li><li class="listitem"><span class="command"><strong>identifier</strong></span> is a link layer
address, specified as a string of hexadecimal digits,</li><li class="listitem"><span class="command"><strong>time</strong></span> is a 32-bit unsigned
time value.</li></ul></div><p>
</p><p>The hexadecimal representation of the DUID generated as a result
of the configuration specified above will be:
</p><pre class="screen">
00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05
------------------------------------------
|type|htype| time | identifier |
</pre><p>
</p><p>It is allowed to use special value of 0 for "htype" and "time",
which indicates that the server should use ANY value for these
components. If the server already uses a DUID-LLT it will use the
values from this DUID. If the server uses a DUID of a different type
or doesn't use any DUID yet, it will generate these values.
Similarly, if the "identifier" is assigned an empty string, the
value of the identifier will be generated. Omitting any of these
parameters is equivalent to setting them to those special values.
</p><p>For example, the following configuration:
</p><pre class="screen">
"Dhcp6": {
"server-id": {
"type": "LLT",
"htype": 0,
"identifier": "",
"time": 2518920166
},
...
}
</pre><p>
indicates that the server should use ANY link layer address and
hardware type. If the server is already using DUID-LLT it will
use link layer address and hardware type from the existing DUID.
If the server is not using any DUID yet, it will use link layer
address and hardware type from one of the available network
interfaces. The server will use explicit value of time. If it
is different than a time value present in the currently used
DUID, this value will be replaced. This will effectively cause
modification of the current server identifier.
</p><p>
The following example demonstrates an explicit configuration of
a DUID-EN:
</p><pre class="screen">
"Dhcp6": {
"server-id": {
"type": "EN",
"enterprise-id": 2495,
"identifier": "87ABEF7A5BB545"
},
...
}
</pre><p>
where:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>enterprise-id</strong></span> is a 32-bit
unsigned value holding enterprise number,</li><li class="listitem"><span class="command"><strong>identifier</strong></span> is a variable
length identifier within DUID-EN.</li></ul></div><p>
</p><p>
The hexadecimal representation of the DUID-EN created according to
the configuration above is:
</p><pre class="screen">
00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45
--------------------------------------
|type| ent-id | identifier |
</pre><p>
</p><p>As in the case of the DUID-LLT, special values can be used for the
configuration of the DUID-EN. If the "enterprise-id" is 0, the server
will use a value from the existing DUID-EN. If the server is not using
any DUID or the existing DUID has a different type, the ISC enterprise
id will be used. When an empty string is used for "identifier", the
identifier from the existing DUID-EN will be used. If the server is
not using any DUID-EN the new 6-bytes long identifier will be generated.
</p><p>DUID-LL is configured in the same way as DUID-LLT with an exception
that the <span class="command"><strong>time</strong></span> parameter has no effect for DUID-LL,
because this DUID type only comprises a hardware type and link layer
address. The following example demonstrates how to configure DUID-LL:
</p><pre class="screen">
"Dhcp6": {
"server-id": {
"type": "LL",
"htype": 8,
"identifier": "A65DC7410F05"
},
...
}
</pre><p>
</p><p>
which will result in the following server identifier:
</p><pre class="screen">
00:03:00:08:A6:5D:C7:41:0F:05
------------------------------
|type|htype| identifier |
</pre><p>
</p><p>Server stores a generated server identifier in the following
location: <strong class="userinput"><code>[kea-install-dir]/var/kea/kea-dhcp6-serverid
</code></strong>.
</p><p>In some uncommon deployments where no stable storage is
available, it is desired to configure the server to not try to
store the server identifier on the stable storage. It is controlled
by the value of <span class="command"><strong>persist</strong></span> boolean parameter:
</p><pre class="screen">
"Dhcp6": {
"server-id": {
"type": "EN",
"enterprise-id": 2495,
"identifier": "87ABEF7A5BB545",
"persist": false
},
...
}
</pre><p>
</p><p>The default value of the "persist" parameter is
<span class="command"><strong>true</strong></span> which configures the server to store the
server identifier on a disk.</p><p>In the example above, the server is configured to not store
the generated server identifier on a disk. But, if the server
identifier is not modified in the configuration the same value
will be used after server restart, because entire server
identifier is explicitly specified in a configuration.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="stateless-dhcp6"></a>8.5. Stateless DHCPv6 (Information-Request Message)</h2></div></div></div><p>Typically DHCPv6 is used to assign both addresses and options. These
assignments (leases) have state that changes over time, hence
their name, stateful. DHCPv6 also supports a stateless mode,
where clients request configuration options only. This mode is
considered lightweight from the server perspective, as it does not require
any state tracking; hence its name.</p><p>The Kea server supports stateless mode. Clients can send
Information-Request messages and the server will send back
answers with the requested options (providing the options are
available in the server configuration). The server will attempt to
use per-subnet options first. If that fails - for whatever reason - it
will then try to provide options defined in the global scope.</p><p>Stateless and stateful mode can be used together. No special
configuration directives are required to handle this. Simply use the
configuration for stateful clients and the stateless clients will get
just options they requested.</p><p>This usage of global options allows for an interesting case.
It is possible to run a server that provides just options and no
addresses or prefixes. If the options have the same value in each
subnet, the configuration can define required options in the global
scope and skip subnet definitions altogether. Here's a simple example of
such a configuration:
</p><pre class="screen">
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "ethX" ]
},
<strong class="userinput"><code>"option-data": [ {
"name": "dns-servers",
"data": "2001:db8::1, 2001:db8::2"
} ]</code></strong>,
"lease-database": { "type": "memfile" }
}
</pre><p>
This very simple configuration will provide DNS server information
to all clients in the network, regardless of their location. Note the
specification of the memfile lease database: this is required since,
as of version 0.9.1, Kea requires a lease database to be specified
even if it is not used.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-rfc7550"></a>8.6. Support for RFC 7550</h2></div></div></div><p>The <a class="ulink" href="http://tools.ietf.org/html/rfc7550" target="_top">RFC 7550</a>
has introduced some changes to the DHCPv6 protocol to resolve a few issues
with the coexistence of multiple stateful options in the messages sent
between the clients and servers.</p><p>The typical example is when the client, such as a requesting
router, requests an allocation of both addresses and prefixes when
it performs the 4-way (SARR) exchange with the server. If the
server is not configured to allocate any prefixes but it can allocate
some addresses, it will respond with the IA_NA(s) containing allocated
addresses and the IA_PD(s) containing the NoPrefixAvail status code. If
the client can operate without prefixes it may transition to the
'bound' state when it sends Renew/Rebind messages to the server,
according to the T1 and T2 times, to extend the lifetimes of the
allocated addresses. If the client is still interested in obtaining
prefixes from the server it may also include IA_PD in the Renew/Rebind
to request allocation of the prefixes. If the server still cannot
allocate the prefixes, it will respond with the IA_PD(s) containing
NoPrefixAvail status code. However, if the server can now allocate
the prefixes it will do so, and send them in the IA_PD(s) to the client.
Allocation of leases during the Renew/Rebind was not supported in the
<a class="ulink" href="http://tools.ietf.org/html/rfc3315" target="_top">RFC 3315</a>
and <a class="ulink" href="http://tools.ietf.org/html/rfc3633" target="_top">RFC 3633</a>,
and has been introduced in
<a class="ulink" href="http://tools.ietf.org/html/rfc7550" target="_top">RFC 7550</a>.
Kea supports this new behavior and it doesn't provide any configuration
mechanisms to disable it.
</p><p>
The following are the other behaviors specified in the
<a class="ulink" href="http://tools.ietf.org/html/rfc7550" target="_top">RFC 7550</a>
supported by the Kea DHCPv6 server:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">set T1/T2 timers to the same value for all
stateful (IA_NA and IA_PD) options to facilitate renewal of all
client's leases at the same time (in a single message exchange),
</li><li class="listitem">NoAddrsAvail and NoPrefixAvail status codes
are placed in the IA_NA and IA_PD options in the Advertise message,
rather than as the top level options.</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-relay-override"></a>8.7. Using specific relay agent for a subnet</h2></div></div></div><p>
The relay has to have an interface connected to the link on which
the clients are being configured. Typically the relay has a global IPv6
address configured on the interface that belongs to the subnet from which
the server will assign addresses. In the typical case, the
server is able to use the IPv6 address inserted by the relay (in the link-addr
field in RELAY-FORW message) to select the appropriate subnet.
</p><p>
However, that is not always the case. The relay
address may not match the subnet in certain deployments. This
usually means that there is more than one subnet allocated for a given
link. The two most common examples where this is the case are long lasting
network renumbering (where both old and new address space is still being
used) and a cable network. In a cable network both cable modems and the
devices behind them are physically connected to the same link, yet
they use distinct addressing. In such case, the DHCPv6 server needs
additional information (like the value of interface-id option or IPv6
address inserted in the link-addr field in RELAY-FORW message) to
properly select an appropriate subnet.
</p><p>
The following example assumes that there is a subnet 2001:db8:1::/64
that is accessible via relay that uses 3000::1 as its IPv6 address.
The server will be able to select this subnet for any incoming packets
that came from a relay that has an address in 2001:db8:1::/64 subnet.
It will also select that subnet for a relay with address 3000::1.
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
<strong class="userinput"><code>"relay": {
"ip-address": "3000::1"
}</code></strong>
}
]
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-client-class-relay"></a>8.8. Segregating IPv6 clients in a cable network</h2></div></div></div><p>
In certain cases, it is useful to mix relay address information,
introduced in <a class="xref" href="#dhcp6-relay-override" title="8.7. Using specific relay agent for a subnet">Section 8.7, “Using specific relay agent for a subnet”</a> with client
classification, explained in <a class="xref" href="#classify" title="Chapter 12. Client Classification">Chapter 12, <i>Client Classification</i></a>.
One specific example is a cable network, where typically modems
get addresses from a different subnet than all devices connected
behind them.
</p><p>
Let's assume that there is one CMTS (Cable Modem Termination System)
with one CM MAC (a physical link that modems are connected to).
We want the modems to get addresses from the 3000::/64 subnet,
while everything connected behind modems should get addresses from
another subnet (2001:db8:1::/64). The CMTS that acts as a relay
an uses address 3000::1. The following configuration can serve
that configuration:
</p><pre class="screen">
"Dhcp6": {
"subnet6": [
{
"subnet": "3000::/64",
"pools": [
{ "pool": "3000::2 - 3000::ffff" }
],
<strong class="userinput"><code>"client-class": "VENDOR_CLASS_docsis3.0",
"relay": {
"ip-address": "3000::1"
}</code></strong>
},
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
<strong class="userinput"><code>"relay": {
"ip-address": "3000::1"
}</code></strong>
}
]
}
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="mac-in-dhcpv6"></a>8.9. MAC/Hardware addresses in DHCPv6</h2></div></div></div><p>MAC/hardware addresses are available in DHCPv4 messages
from the clients and administrators
frequently use that information to perform certain tasks, like per host
configuration, address reservation for specific MAC addresses and other.
Unfortunately, the DHCPv6 protocol does not provide any completely reliable way
to retrieve that information. To mitigate that issue a number of mechanisms
have been implemented in Kea that attempt to gather that information. Each
of those mechanisms works in certain cases, but may fail in other cases.
Whether the mechanism works or not in the particular deployment is
somewhat dependent on the network topology and the technologies used.</p><p>Kea allows for configuration which of the supported methods should be
used and in which order. This configuration may be considered a fine tuning
of the DHCP deployment. In a typical deployment the default
value of <span class="command"><strong>"any"</strong></span> is sufficient and there is no
need to select specific methods. Changing the value of this parameter
is the most useful in cases when an administrator wants to disable
certain method, e.g. if the administrator trusts the network infrastructure
more than the information provided by the clients themselves, the
administrator may prefer information provided by the relays over that
provided by the clients. The format of this parameter is as follows:
</p><pre class="screen">
"Dhcp6": {
<strong class="userinput"><code>"mac-sources": [ "method1", "method2", "method3", ... ]</code></strong>,
"subnet6": [ ... ],
...
}
</pre><p>
When not specified, a special value of <span class="emphasis"><em>any</em></span> is used, which
instructs the server to attempt to use all the methods in sequence and use
value returned by the first one that succeeds.</p><p>Supported methods are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>any</strong></span> - not an actual method, just a keyword that
instructs Kea to try all other methods and use the first one that succeeds.
This is the default operation if no <span class="command"><strong>mac-sources</strong></span> are defined.
</li><li class="listitem"><span class="command"><strong>raw</strong></span> - In principle, a DHCPv6 server could use raw
sockets to receive incoming traffic and extract MAC/hardware address
information. This is currently not implemented for DHCPv6 and this value has
no effect.
</li><li class="listitem"><span class="command"><strong>duid</strong></span> - DHCPv6 uses DUID identifiers instead of
MAC addresses. There are currently four DUID types defined, with two of them
(DUID-LLT, which is the default one and DUID-LL) convey MAC address information.
Although RFC 3315 forbids it, it is possible to parse those DUIDs and extract
necessary information from them. This method is not completely reliable, as
clients may use other DUID types, namely DUID-EN or DUID-UUID.
</li><li class="listitem"><span class="command"><strong>ipv6-link-local</strong></span> - Another possible acquisition
method comes from the source IPv6 address. In typical usage, clients are
sending their packets from IPv6 link-local addresses. There's a good chance
that those addresses are based on EUI-64, which contains MAC address. This
method is not completely reliable, as clients may use other link-local address
types. In particular, privacy extensions, defined in RFC 4941, do not use
MAC addresses. Also note that successful extraction requires that the
address's u-bit must be set to 1 and its g-bit set to 0, indicating that it
is an interface identifier as per
<a class="ulink" href="http://tools.ietf.org/html/rfc2373#section-2.5.1" target="_top">
RFC 2373, section 2.5.1</a>.
</li><li class="listitem"><span class="command"><strong>client-link-addr-option</strong></span> - One extension defined
to alleviate missing MAC issues is client link-layer address option, defined
in <a class="ulink" href="http://tools.ietf.org/html/rfc6939" target="_top">RFC 6939</a>. This is
an option that is inserted by a relay and contains information about client's
MAC address. This method requires a relay agent that supports the option and
is configured to insert it. This method is useless for directly connected
clients. This parameter can also be specified as <span class="command"><strong>rfc6939</strong></span>,
which is an alias for <span class="command"><strong>client-link-addr-option</strong></span>.
</li><li class="listitem"><span class="command"><strong>remote-id</strong></span> - <a class="ulink" href="http://tools.ietf.org/html/rfc4649" target="_top">RFC 4649</a>
defines remote-id option that is inserted by a relay agent. Depending
on the relay agent configuration, the inserted option may convey client's
MAC address information. This parameter can also be specified as
<span class="command"><strong>rfc4649</strong></span>, which is an alias for <span class="command"><strong>remote-id</strong></span>.
</li><li class="listitem"><span class="command"><strong>subscriber-id</strong></span> - Another option
that is somewhat similar to the previous one is subscriber-id,
defined in <a class="ulink" href="http://tools.ietf.org/html/rfc4580" target="_top">RFC
4580</a>. It is, too, inserted by a relay agent that is
configured to insert it. This parameter can also be specified
as <span class="command"><strong>rfc4580</strong></span>, which is an alias for
<span class="command"><strong>subscriber-id</strong></span>. This method is currently not
implemented.
</li><li class="listitem"><span class="command"><strong>docsis-cmts</strong></span> - Yet another possible source of MAC
address information are DOCSIS options inserted by a CMTS that acts
as a DHCPv6 relay agent in cable networks. This method attempts to extract
MAC address information from suboption 1026 (cm mac) of the vendor specific option
with vendor-id=4491. This vendor option is extracted from the relay-forward message,
not the original client's message.
</li><li class="listitem"><span class="command"><strong>docsis-modem</strong></span> - Yet another possible source of MAC
address information are DOCSIS options inserted by the cable modem itself.
This method attempts to extract MAC address information from suboption 36 (device id)
of the vendor specific option with vendor-id=4491. This vendor option is extracted from
the original client's message, not from any relay options.
</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-decline"></a>8.10. Duplicate Addresses (DECLINE support)</h2></div></div></div><p>The DHCPv6 server is configured with a certain pool of
addresses that it is expected to hand out to the DHCPv6 clients.
It is assumed that the server is authoritative and has complete
jurisdiction over those addresses. However, due to various
reasons, such as misconfiguration or a faulty client implementation
that retains its address beyond the valid lifetime, there may be
devices connected that use those addresses without the server's
approval or knowledge.</p><p>Such an unwelcome event can be detected
by legitimate clients (using Duplicate Address Detection) and
reported to the DHCPv6 server using a DECLINE message. The server
will do a sanity check (if the client declining an address really
was supposed to use it), then will a conduct clean up operation
and confirm it by sending back a REPLY message. Any DNS entries
related to that address will be removed, the fact will be logged
and hooks will be triggered. After that is done, the address
will be marked as declined (which indicates that it is used by
an unknown entity and thus not available for assignment to
anyone) and a probation time will be set on it. Unless otherwise
configured, the probation period lasts 24 hours. After that
period, the server will recover the lease, i.e. put it back into
the available state. The address will be available for assignment
again. It should be noted that if the underlying issue of a
misconfigured device is not resolved, the duplicate address
scenario will repeat. On the other hand, it provides an
opportunity to recover from such an event automatically, without
any sysadmin intervention.</p><p>To configure the decline probation period to a value different
than the default, the following syntax can be used:
</p><pre class="screen">
"Dhcp6": {
<strong class="userinput"><code>"decline-probation-period": 3600</code></strong>,
"subnet6": [ ... ],
...
}
</pre><p>
The parameter is expressed in seconds, so the example above will instruct
the server to recycle declined leases after an hour.</p><p>There are several statistics and hook points associated with the
Decline handling procedure. The lease6_decline hook is triggered after the
incoming Decline message has been sanitized and the server is about to decline
the lease. The declined-addresses statistic is increased after the hook
returns (both global and subnet specific variants).</p><p>Once the probation time elapses, the declined lease is recovered
using the standard expired lease reclamation procedure, with several
additional steps. In particular, both declined-addresses statistics
(global and subnet specific) are decreased. At the same time,
reclaimed-declined-addresses statistics (again in two variants, global and
subnet specific) are increased.</p><p>Note about statistics: The server does not decrease
assigned-addresses statistics when a DECLINE message is received and
processed successfully. While technically a declined address is no longer
assigned, the primary usage of the assigned-addresses statistic is to
monitor pool utilization. Most people would forget to include
declined-addresses in the calculation, and simply do
assigned-addresses/total-addresses. This would have a bias towards
under-representing pool utilization. As this has a potential for major
issues, we decided not to decrease assigned addresses immediately after
receiving Decline, but to do it later when we recover the address back to
the available pool.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-stats"></a>8.11. Statistics in DHCPv6 server</h2></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This section describes DHCPv6-specific statistics. For a general
overview and usage of statistics, see <a class="xref" href="#stats" title="Chapter 14. Statistics">Chapter 14, <i>Statistics</i></a>.</p></div><p>
The DHCPv6 server supports the following statistics:
</p><div class="table"><a name="dhcp6-statistics"></a><p class="title"><b>Table 8.4. DHCPv6 Statistics</b></p><div class="table-contents"><table summary="DHCPv6 Statistics" border="1"><colgroup><col align="center" class="statistic"><col align="center" class="type"><col align="left" class="description"></colgroup><thead><tr><th align="center">Statistic</th><th align="center">Data Type</th><th align="left">Description</th></tr></thead><tbody><tr><td align="center">pkt6-received</td><td align="center">integer</td><td align="left">Number of DHCPv6 packets received. This includes all packets:
valid, bogus, corrupted, rejected etc. This statistic is expected
to grow rapidly.</td></tr><tr><td align="center">pkt6-receive-drop</td><td align="center">integer</td><td align="left">Number of incoming packets that were dropped. Exact reason
for dropping packets is logged, but the most common reasons may
be: an unacceptable or not supported packet type, direct responses
are forbidden, the server-id sent by the client does not match the
server's server-id or the packet is malformed.</td></tr><tr><td align="center">pkt6-parse-failed</td><td align="center">integer</td><td align="left">Number of incoming packets that could not be parsed.
A non-zero value of this statistic indicates that the server
received a malformed or truncated packet. This may indicate problems
in your network, faulty clients, faulty relay agents or server
code bug.</td></tr><tr><td align="center">pkt6-solicit-received</td><td align="center">integer</td><td align="left">
Number of SOLICIT packets received. This statistic is expected
to grow. Its increase means that clients that just booted
started their configuration process and their initial packets
reached your server.
</td></tr><tr><td align="center">pkt6-advertise-received</td><td align="center">integer</td><td align="left">
Number of ADVERTISE packets received. Advertise packets are sent
by the server and the server is never expected to receive them. A non-zero
value of this statistic indicates an error occurring in the network.
One likely cause would be a misbehaving relay agent that incorrectly
forwards ADVERTISE messages towards the server, rather back to the
clients.
</td></tr><tr><td align="center">pkt6-request-received</td><td align="center">integer</td><td align="left">Number of REQUEST packets received. This statistic
is expected to grow. Its increase means that clients that just booted
received the server's response (ADVERTISE), accepted it and are now
requesting an address (REQUEST).
</td></tr><tr><td align="center">pkt6-reply-received</td><td align="center">integer</td><td align="left">Number of REPLY packets received. This statistic is
expected to remain zero at all times, as REPLY packets are sent by
the server and the server is never expected to receive
them. A non-zero value indicates an error. One likely cause would be
a misbehaving relay agent that incorrectly forwards REPLY messages
towards the server, rather back to the clients.
</td></tr><tr><td align="center">pkt6-renew-received</td><td align="center">integer</td><td align="left">Number of RENEW packets received. This statistic
is expected to grow. Its increase means that clients received their
addresses and prefixes and are trying to renew them.
</td></tr><tr><td align="center">pkt6-rebind-received</td><td align="center">integer</td><td align="left">Number of REBIND packets received. A non-zero value
indicates that clients didn't receive responses to their RENEW messages
(regular lease renewal mechanism) and are attempting to find any server
that is able to take over their leases. It may mean that some server's
REPLY messages never reached the clients.
</td></tr><tr><td align="center">pkt6-release-received</td><td align="center">integer</td><td align="left">Number of RELEASE packets received. This statistic is expected
to grow when a device is being shut down in the network. It
indicates that the address or prefix assigned is reported as no longer
needed. Note that many devices, especially wireless, do not send RELEASE,
because of design choice or due to moving out of range.
</td></tr><tr><td align="center">pkt6-decline-received</td><td align="center">integer</td><td align="left">
Number of DECLINE packets received. This statistic is expected to
remain close to zero. Its increase means that a client leased an
address, but discovered that the address is currently used by an
unknown device in your network. If this statistic is growing, it
may indicate misconfigured server or devices that have statically
assigned conflicting addresses.
</td></tr><tr><td align="center">pkt6-infrequest-received</td><td align="center">integer</td><td align="left">
Number of INFORMATION-REQUEST packets received. This statistic
is expected to grow if there are devices that are using
stateless DHCPv6. INFORMATION-REQUEST messages are used by
clients that request stateless configuration, i.e. options
and parameters other than addresses or prefixes.
</td></tr><tr><td align="center">pkt6-unknown-received</td><td align="center">integer</td><td align="left">Number of packets received of an unknown type. Non-zero
value of this statistic indicates that the server received a
packet that it wasn't able to recognize: either with unsupported
type or possibly malformed.</td></tr><tr><td align="center">pkt6-sent</td><td align="center">integer</td><td align="left">Number of DHCPv6 packets sent. This statistic is expected
to grow every time the server transmits a packet. In general, it
should roughly match pkt6-received, as most incoming packets cause
the server to respond. There are exceptions (e.g. server receiving a
REQUEST with server-id matching other server), so do not worry, if
it is lesser than pkt6-received.</td></tr><tr><td align="center">pkt6-advertise-sent</td><td align="center">integer</td><td align="left">Number of ADVERTISE packets sent. This statistic is
expected to grow in most cases after a SOLICIT is processed. There
are certain uncommon, but valid cases where incoming SOLICIT is
dropped, but in general this statistic is expected to be close to
pkt6-solicit-received.</td></tr><tr><td align="center">pkt6-reply-sent</td><td align="center">integer</td><td align="left">Number of REPLY packets sent. This statistic is expected to
grow in most cases after a SOLICIT (with rapid-commit), REQUEST,
RENEW, REBIND, RELEASE, DECLINE or INFORMATION-REQUEST is
processed. There are certain cases where there is no response.
</td></tr><tr><td align="center">subnet[id].total-nas</td><td align="center">integer</td><td align="left">
This statistic shows the total number of NA addresses available for
DHCPv6 management for a given subnet. In other words, this is the sum
of all addresses in all configured pools. This statistic changes only
during configuration changes. Note it does not take into account any
addresses that may be reserved due to host reservation. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately. This statistic is
reset during a reconfiguration event.
</td></tr><tr><td align="center">subnet[id].assigned-nas</td><td align="center">integer</td><td align="left">
This statistic shows the number of NA addresses in a given subnet that
are assigned. This statistic increases every time a new lease is allocated
(as a result of receiving a REQUEST message) and is decreased every time a
lease is released (a RELEASE message is received) or expires. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately. This statistic is
reset during a reconfiguration event.
</td></tr><tr><td align="center">subnet[id].total-pds</td><td align="center">integer</td><td align="left">
This statistic shows the total number of PD prefixes available for
DHCPv6 management for a given subnet. In other words, this is the sum
of all prefixes in all configured pools. This statistic changes only
during configuration changes. Note it does not take into account any
prefixes that may be reserved due to host reservation. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately. This statistic is
reset during a reconfiguration event.
</td></tr><tr><td align="center">subnet[id].assigned-pds</td><td align="center">integer</td><td align="left">
This statistic shows the number of PD prefixes in a given subnet that
are assigned. This statistic increases every time a new lease is allocated
(as a result of receiving a REQUEST message) and is decreased every time a
lease is released (a RELEASE message is received) or expires. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This statistic
is exposed for each subnet separately. This statistic is reset during a
reconfiguration event.
</td></tr><tr><td align="center">declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv6 addresses that are
currently declined. This statistic counts the number of leases
currently unavailable. Once a lease is recovered, this
statistic will be decreased. Ideally, this statistic should be
zero. If this statistic is non-zero (or worse increasing),
a network administrator should investigate if there is
a misbehaving device in his network. This is a global statistic
that covers all subnets.
</td></tr><tr><td align="center">subnet[id].declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv6 addresses that are
currently declined in a given subnet. This statistic counts the
number of leases currently unavailable. Once a lease is
recovered, this statistic will be decreased. Ideally, this
statistic should be zero. If this statistic is
non-zero (or worse increasing), a network administrator should
investigate if there is a misbehaving device in his network. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately.
</td></tr><tr><td align="center">reclaimed-declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv6 addresses that were
declined, but have now been recovered. Unlike
declined-addresses, this statistic never decreases. It can be used
as a long term indicator of how many actual valid Declines were
processed and recovered from. This is a global statistic that
covers all subnets.
</td></tr><tr><td align="center">subnet[id].reclaimed-declined-addresses</td><td align="center">integer</td><td align="left">
This statistic shows the number of IPv6 addresses that were
declined, but have now been recovered. Unlike
declined-addresses, this statistic never decreases. It can be used
as a long term indicator of how many actual valid Declines were
processed and recovered from. The
<span class="emphasis"><em>id</em></span> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately.
</td></tr></tbody></table></div></div><br class="table-break"></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-ctrl-channel"></a>8.12. Management API for the DHCPv6 server</h2></div></div></div><p>
Management API has been introduced in Kea 0.9.2-beta. It allows issuing specific
management commands, like statistics retrieval, reconfiguration or shutdown.
For more details, see <a class="xref" href="#ctrl-channel" title="Chapter 15. Management API">Chapter 15, <i>Management API</i></a>. Currently the only
supported communication channel type is UNIX stream socket. By default there
are no sockets open. To instruct Kea to open a socket, the following entry
in the configuration file can be used:
</p><pre class="screen">
"Dhcp6": {
"control-socket": {
"socket-type": "unix",
"socket-name": <strong class="userinput"><code>"/path/to/the/unix/socket"</code></strong>
},
"subnet6": [
...
],
...
}
</pre><p>
</p><p>
The length of the path specified by the <span class="command"><strong>socket-name</strong></span>
parameter is restricted by the maximum length for the unix socket name
on your operating system, i.e. the size of the <span class="command"><strong>sun_path</strong></span>
field in the <span class="command"><strong>sockaddr_un</strong></span> structure, decreased by 1.
This value varies on different operating systems between 91 and 107
characters. The typical values are 107 on Linux and 103 on FreeBSD.
</p><p>
Communication over control channel is conducted using JSON structures.
See the Control Channel section in the Kea Developer's Guide for more details.
</p><p>DHCPv6 server supports <span class="command"><strong>statistic-get</strong></span>,
<span class="command"><strong>statistic-reset</strong></span>, <span class="command"><strong>statistic-remove</strong></span>,
<span class="command"><strong>statistic-get-all</strong></span>, <span class="command"><strong>statistic-reset-all</strong></span>
and <span class="command"><strong>statistic-remove-all</strong></span>, specified in
<a class="xref" href="#command-stats" title="14.3. Commands for Manipulating Statistics">Section 14.3, “Commands for Manipulating Statistics”</a>. It also supports
<span class="command"><strong>list-commands</strong></span> and <span class="command"><strong>shutdown</strong></span>,
specified in <a class="xref" href="#command-list-commands" title="15.3.2. list-commands command">Section 15.3.2, “list-commands command”</a> and
<a class="xref" href="#command-shutdown" title="15.3.3. shutdown command">Section 15.3.3, “shutdown command”</a>, respectively.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-std"></a>8.13. Supported DHCPv6 Standards</h2></div></div></div><p>The following standards are currently
supported:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="emphasis"><em>Dynamic Host Configuration Protocol for IPv6</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc3315" target="_top">RFC 3315</a>:
Supported messages are SOLICIT,
ADVERTISE, REQUEST, RELEASE, RENEW, REBIND, INFORMATION-REQUEST,
CONFIRM and REPLY.</li><li class="listitem"><span class="emphasis"><em>IPv6 Prefix Options for
Dynamic Host Configuration Protocol (DHCP) version 6</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc3633" target="_top">RFC 3633</a>:
Supported options are IA_PD and
IA_PREFIX. Also supported is the status code NoPrefixAvail.</li><li class="listitem"><span class="emphasis"><em>DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc3646" target="_top">RFC 3646</a>:
Supported option is DNS_SERVERS.</li><li class="listitem"><span class="emphasis"><em>The Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Relay Agent Remote-ID Option</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc4649" target="_top">RFC 4649</a>:
REMOTE-ID option is supported.</li><li class="listitem"><span class="emphasis"><em>The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client
Fully Qualified Domain Name (FQDN) Option</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc4704" target="_top">RFC 4704</a>:
Supported option is CLIENT_FQDN.</li><li class="listitem"><span class="emphasis"><em>Relay-Supplied DHCP Options</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc6422" target="_top">RFC 6422</a>:
Full functionality is supported: OPTION_RSOO, ability of the server
to echo back the options, checks whether an option is RSOO-enabled,
ability to mark additional options as RSOO-enabled.</li><li class="listitem"><span class="emphasis"><em>Client Link-Layer Address Option in
DHCPv6</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc6939" target="_top">RFC
6939</a>: Supported option is client link-layer
address option.</li><li class="listitem"><span class="emphasis"><em>Issues and Recommendations with Multiple
Stateful DHCPv6 Options</em></span>,
<a class="ulink" href="http://tools.ietf.org/html/rfc7550" target="_top">RFC
7550</a>: All recommendations related to the DHCPv6 server
operation are supported.</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp6-limit"></a>8.14. DHCPv6 Server Limitations</h2></div></div></div><p> These are the current limitations and known problems
with the DHCPv6 server
software. Most of them are reflections of the early stage of
development and should be treated as <span class="quote">“<span class="quote">not implemented
yet</span>”</span>, rather than actual limitations.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
On-line configuration has some limitations. Adding new subnets or
modifying existing ones work, as is removing the last subnet from
the list. However, removing non-last (e.g. removing subnet 1,2 or 3 if
there are 4 subnets configured) will cause issues. The problem is
caused by simplistic subnet-id assignment. The subnets are always
numbered, starting from 1. That subnet-id is then used in leases
that are stored in the lease database. Removing non-last subnet will
cause the configuration information to mismatch data in the lease
database. It is possible to manually update subnet-id fields in
MySQL or PostgreSQL database, but it is awkward and error prone
process. A better reconfiguration support is planned.
</p></li><li class="listitem">
The server will allocate, renew or rebind a maximum of one lease
for a particular IA option (IA_NA or IA_PD) sent by a client.
<a class="ulink" href="http://tools.ietf.org/html/rfc3315" target="_top">RFC 3315</a> and
<a class="ulink" href="http://tools.ietf.org/html/rfc3633" target="_top">RFC 3633</a> allow
for multiple addresses or prefixes to be allocated for a single IA.
</li><li class="listitem">Temporary addresses are not supported.</li><li class="listitem">
Duplication report (DECLINE) and client reconfiguration (RECONFIGURE) are
not yet supported.
</li></ul></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="lease-expiration"></a>Chapter 9. Lease Expiration in DHCPv4 and DHCPv6</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#lease-reclamation">9.1. Lease Reclamation</a></span></dt><dt><span class="section"><a href="#lease-reclaim-config">9.2. Configuring Leases Reclamation</a></span></dt><dt><span class="section"><a href="#lease-affinity">9.3. Configuring Lease Affinity</a></span></dt><dt><span class="section"><a href="#lease-reclamation-defaults">9.4. Default Configuration Values for Leases Reclamation</a></span></dt><dt><span class="section"><a href="#leases-reclamation-using-command">9.5. Reclaiming Expired Leases with Command</a></span></dt></dl></div><p>The primary role of the DHCP server is to assign addresses and/or
delegate prefixes to DHCP clients. These addresses and prefixes are
often referred to as 'leases'. Leases are typically assigned to clients
for a finite amount of time, known as 'valid lifetime'. DHCP clients who
wish to continue using their assigned leases, will periodically renew them
by sending the appropriate message to the DHCP server. The DHCP server records
the time when these leases are renewed and calculates new expiration times
for them.
</p><p>If the client does not renew a lease before its valid lifetime
elapses, the lease is considered expired. There are many situations
when the client may cease lease renewals. A common scenario is when
the machine running the client shuts down for an extended period of
time.</p><p> The process through which the DHCP server makes expired leases
available for reassignment is referred to as "lease reclamation" and expired
leases returned to availability through this process are referred to as
"reclaimed".
The DHCP server should reclaim an expired lease as soon as it detects
that it has expired. One way in which the server may detect expiration
is when it is trying to allocate a lease to a client and finds this
lease already present in the database but expired. Another way the
server detects expired leases is by periodically querying the lease
database for them. Regardless of how an expired lease is detected, before
it my assigned to a client, it must be reclaimed.
This chapter explains how to configure the server to periodically query
for the expired leases and how to minimize the impact of the periodic leases
reclamation process on the server's responsiveness. Finally, 'lease affinity',
which provides the means to assign the same lease to the returning client
after its lease has expired, is explained.
</p><p>Although, all configuration examples in this section are provided
for the DHCPv4 server, the same parameters may be used for the
DHCPv6 server configuration.
</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="lease-reclamation"></a>9.1. Lease Reclamation</h2></div></div></div><p>Lease reclamation is the process through which an expired lease
becomes available for assignment to the same or a different client.
This process involves the following steps for each reclaimed lease:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Invoke callouts for the <span class="command"><strong>lease4_expire</strong></span> or
<span class="command"><strong>lease6_expire</strong></span> hook points, if hook libraries
supporting those callouts are currently loaded.</li><li class="listitem">Update DNS, i.e. remove any DNS entries associated with
the expired lease.</li><li class="listitem">Update lease information in the lease database to
indicate that the lease is now available for re-assignment.</li><li class="listitem">Update statistics of the server, which includes
increasing the number of reclaimed leases and decreasing the
number of assigned addresses or delegated prefixes etc.</li></ul></div><p>Please refer to <a class="xref" href="#dhcp-ddns-server" title="Chapter 10. The DHCP-DDNS Server">Chapter 10, <i>The DHCP-DDNS Server</i></a> to see
how to configure DNS updates in Kea, and to
<a class="xref" href="#hooks-libraries" title="Chapter 13. Hooks Libraries">Chapter 13, <i>Hooks Libraries</i></a> for information about using
hooks libraries.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="lease-reclaim-config"></a>9.2. Configuring Leases Reclamation</h2></div></div></div><p>Kea can be configured to periodically detect and reclaim expired
leases. During this process the lease entries in the database are
modified or removed. Therefore the server will not process incoming DHCP
messages to avoid issues with concurrent access to database information.
As a result, the server will be unresponsive while lease reclamation
is performed. DHCP queries will accumulate and responses will be
sent once the leases reclamation cycle is complete.</p><p>In deployments where response time is critical, administrators may
wish to minimize the interruptions in service caused by lease reclamation.
Toward this end, Kea provides configuration parameters to control: the
frequency of lease reclamation cycles, the maximum number of leases
processed in a single reclamation cycle, and the maximum amount of time a
single reclamation cycle is allowed to run before being interrupted. The
following examples demonstrate how these parameters can be used:
</p><pre class="screen">
"Dhcp4": {
...
"expired-leases-processing": {
"reclaim-timer-wait-time": 5,
"max-reclaim-leases": 0,
"max-reclaim-time": 0,
"flush-reclaimed-timer-wait-time": 0,
},
...
}
</pre><p>
</p><p>The first parameter is expressed in seconds and specifies an
interval between the two consecutive lease reclamation cycles. This
is explained on the following diagram.
</p><pre class="screen">
| c1 | | c2 | |c3| | c4 |
|<---->|<---------->|<-->|<---------->|<>|<---------->|<-->|
---------------------------------------------------------------->
| | 5s | | 5s | | 5s | | time
</pre><p>
</p><p>This diagram shows 4 leases reclamation cycles of variable duration.
Note that the duration of the reclamation cycle depends on the number
of expired leases detected and processed in the particular cycle. This
duration is also usually significantly shorter than the interval between
the cycles.
</p><p>According to the <span class="command"><strong>reclaim-timer-wait-time</strong></span> the
server keeps fixed intervals of 5 seconds between the end of one cycle
and the start of the next cycle. This guarantees the presence of
5s long periods during which the server remains responsive to DHCP
queries and does not perform leases reclamation. The
<span class="command"><strong>max-reclaim-leases</strong></span> and
<span class="command"><strong>max-reclaim-time</strong></span> are set to 0, which implies that
there is no restriction on the maximum number of leases reclaimed
in the particular cycle, or the maximum duration of each cycle.
</p><p>In deployments with high lease pool utilization, relatively
short valid lifetimes, and frequently disconnecting clients which
allow leases to expire; the number of expired leases requiring reclamation
at any given time may rise significantly. In this case it is often
desirable to apply restrictions on the maximum duration of a reclamation
cycle or the maximum number of leases reclaimed in a cycle. The following
configuration demonstrates how this can be done:
</p><pre class="screen">
"Dhcp4": {
...
"expired-leases-processing": {
"reclaim-timer-wait-time": 3,
"max-reclaim-leases": 100,
"max-reclaim-time": 50,
"unwarned-reclaim-cycles": 10,
"flush-reclaimed-timer-wait-time": 0,
},
...
}
</pre><p>
</p><p>The <span class="command"><strong>max-reclaim-leases</strong></span> parameter limits the number
of leases reclaimed in a single cycle to 100. The
<span class="command"><strong>max-reclaim-time</strong></span> limits the maximum duration of each
cycle to 50ms. The lease reclamation cycle will be interrupted if either
of these limitations is reached. The reclamation of all unreclaimed
leases will be attempted in subsequent cycles.</p><p>The following diagram illustrates the behavior of the system in the
presence of many expired leases, when the limits are applied for the
reclamation cycles.
</p><pre class="screen">
| c1 | | c2 | | c3 | | c4 |
|<-->|<-------------->|<-->|<-------------->|<-->|<-------------->|<-->|<--
------------------------------------------------------------------------------>
|50ms| 3s |50ms| 3s |50ms| 3s |50ms| time
</pre><p>
</p><p>The diagram demonstrates the case when each reclamation cycle would take
more than 50ms, and thus is interrupted according to the value of the
<span class="command"><strong>max-reclaim-time</strong></span>. This results in equal durations of
all reclamation cycles over time. Note that in this example the limitation
of maximum 100 leases is not reached. This may be the case when database
transactions are slow or callouts in the hook libraries attached to
the server are slow. Regardless, the choosing values for either the
maximum number of leases or a maximum cycle time strongly depends on the
particular deployment, lease database backend being used, and any hooks
libraries etc. Administrators may need to experiment to tune the system
to suit the dynamics of their deployment.</p><p>It is important to realize that with the use of these limits, there
is a risk that expired leases will accumulate faster than the server can
reclaim them. This should not be the problem if the server is dealing
with a temporary burst of expirations, because it should be able to
eventually deal with them over time. However, if leases expire at the high
rate for a longer period of time, the unreclaimed leases will pile up in
the database. In order to notify the administrator that the current
configuration does not satisfy the needs for reclamation of expired
leases, the server issues a warning message in the log, if it was unable
to reclaim all leases within the last couple of reclamation cycles. The
number of cycles after which such warning is issued is specified with the
<span class="command"><strong>unwarned-reclaim-cycles</strong></span> configuration parameter.
</p><p>Setting the <span class="command"><strong>reclaim-timer-wait-time</strong></span> to 0 disables
periodic reclamation of the expired leases.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="lease-affinity"></a>9.3. Configuring Lease Affinity</h2></div></div></div><p>Suppose that a laptop goes to a sleep mode after a period of user
inactivity. While the laptop is in sleep mode, its DHCP client will not
renew leases obtained from the server and these leases will eventually
expire. When the laptop wakes up, it is often desired that it continue
using its previous assigned IP addresses. In order to facilitate this,
the server needs to correlate returning clients with their expired leases
When the client returns, the server will first check for those leases and
re-assign them if they have not assigned to another client. The ability
of the server to re-assign the same lease to a returning client is
referred to as 'lease affinity'.
</p><p>When lease affinity is enabled, the server will still
reclaim leases according to the parameters described in
<a class="xref" href="#lease-reclaim-config" title="9.2. Configuring Leases Reclamation">Section 9.2, “Configuring Leases Reclamation”</a>, but the reclaimed leases
will be held in the database (rather than removed) for the specified
amount of time. When the client returns, the server will first check
if there are any reclaimed leases associated with this client and
re-assign them if possible. However, it is important to note that
any reclaimed lease may be assigned to another client if that client
specifically asks for it. Therefore, the lease affinity does not
guarantee that the reclaimed lease will be available for the client
who used it before. It merely increases the chances for the client to
be assigned the same lease. If the lease pool is small (mostly applies
to DHCPv4 for which address space is small), there is an increased
likelihood that the expired lease will be hijacked by another client.
</p><p>Consider the following configuration:
</p><pre class="screen">
"Dhcp4": {
...
"expired-leases-processing": {
"reclaim-timer-wait-time": 3,
"hold-reclaimed-time": 1800,
"flush-reclaimed-timer-wait-time": 5
},
...
}
</pre><p>
</p><p>The <span class="command"><strong>hold-reclaim-time</strong></span> specifies how many seconds
after an expiration a reclaimed lease should be held in the database
for re-assignment to the same client. In the example given above,
reclaimed leases will be held for 30 minutes (1800s) after their
expiration. During this time, the server will likely be able to
re-assign the same lease to the returning client, unless another client
requests this lease and the server assigns it.</p><p>The server must periodically remove reclaimed leases for which the
time indicated by <span class="command"><strong>hold-reclaim-time</strong></span> has elapsed. The
<span class="command"><strong>flush-reclaimed-timer-wait-time</strong></span> controls how
often the server removes such leases. In the example provided
above, the server will initiate removal of such leases 5 seconds after
the previous removal attempt was completed. Setting this value to 0
disables lease affinity, in which case leases will be removed from the
lease database when they are reclaimed. If lease affinity is enabled, it
is recommended that hold-reclaim-time be set to a value significantly
higher than the <span class="command"><strong>reclaim-timer-wait-time</strong></span>, as timely
removal of expired-reclaimed leases is less critical while the removal
process may impact server responsiveness.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="lease-reclamation-defaults"></a>9.4. Default Configuration Values for Leases Reclamation</h2></div></div></div><p>The following list presents all configuration parameters
pertaining to processing expired leases with their default values:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>reclaim-timer-wait-time</strong></span> = 10 [seconds]</li><li class="listitem"><span class="command"><strong>flush-reclaimed-timer-wait-time</strong></span> = 25 [seconds]</li><li class="listitem"><span class="command"><strong>hold-reclaimed-time</strong></span> = 3600 [seconds]</li><li class="listitem"><span class="command"><strong>max-reclaim-leases</strong></span> = 100 </li><li class="listitem"><span class="command"><strong>max-reclaim-time</strong></span> = 250 [milliseconds]</li><li class="listitem"><span class="command"><strong>unwarned-reclaim-cycles</strong></span> = 5</li></ul></div><p>The default value for any parameter is used when this parameter not
explicitly specified in the configuration. Also, the
<span class="command"><strong>expired-leases-processing</strong></span> map may be omitted entirely
in the configuration, in which case the default values are used for all
parameters listed above.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="leases-reclamation-using-command"></a>9.5. Reclaiming Expired Leases with Command</h2></div></div></div><p>The <span class="emphasis"><em>leases-reclaim</em></span> command can be used to trigger
leases reclamation at any time. Please consult the
<a class="xref" href="#command-leases-reclaim" title="15.3.1. leases-reclaim command">Section 15.3.1, “leases-reclaim command”</a> for the details about using this
command.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="dhcp-ddns-server"></a>Chapter 10. The DHCP-DDNS Server</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#dhcp-ddns-server-start-stop">10.1. Starting and Stopping the DHCP-DDNS Server</a></span></dt><dt><span class="section"><a href="#d2-configuration">10.2. Configuring the DHCP-DDNS Server</a></span></dt><dd><dl><dt><span class="section"><a href="#d2-server-parameter-config">10.2.1. Global Server Parameters</a></span></dt><dt><span class="section"><a href="#d2-tsig-key-list-config">10.2.2. TSIG Key List</a></span></dt><dt><span class="section"><a href="#d2-forward-ddns-config">10.2.3. Forward DDNS</a></span></dt><dt><span class="section"><a href="#d2-reverse-ddns-config">10.2.4. Reverse DDNS</a></span></dt><dt><span class="section"><a href="#d2-exmaple-config">10.2.5. Example DHCP-DDNS Server Configuration</a></span></dt></dl></dd><dt><span class="section"><a href="#idp55495520">10.3. DHCP-DDNS Server Limitations</a></span></dt></dl></div><p>
The DHCP-DDNS Server (kea-dhcp-ddns, known informally as D2) conducts the client side of
the DDNS protocol (defined in RFC 2136) on behalf of the DHCPv4 and DHCPv6
servers (kea-dhcp4 and kea-dhcp6 respectively). The DHCP servers construct
DDNS update requests, known as NameChangeRequests (NCRs), based upon DHCP
lease change events and then post these to D2. D2 attempts to match
each such request to the appropriate DNS server(s) and carry out the
necessary conversation with those servers to update the DNS data.
</p><p>
In order to match a request to the appropriate DNS servers, D2 must have a
catalog of servers from which to select. In fact, D2 has two such catalogs,
one for forward DNS and one for reverse DNS; these catalogs are referred
to as DDNS Domain Lists. Each list consists of one or more named DDNS
Domains. Further, each DDNS Domain has a list of one or more DNS
servers that publish the DNS data for that domain.
</p><p>
When conducting forward domain matching, D2 will compare the FQDN in
the request against the name of each forward DDNS Domain. The domain
whose name matches the longest portion of the FQDN is considered the
best match. For example, if the FQDN is "myhost.sample.example.com.",
and there are two forward domains in the catalog: "sample.example.com."
and "example.com.", the former is regarded as the best match. In some
cases, it may not be possible to find a suitable match. Given the same two
forward domains there would be no match for the FQDN, "bogus.net", so the
request would be rejected. Finally, if there are no forward DDNS Domains
defined, D2 will simply disregard the forward update portion of requests.
</p><p>
When conducting reverse domain matching, D2 constructs a reverse
FQDN from the lease address in the request and compare that against
the name of each reverse DDNS Domain. Again, the domain whose name matches
the longest portion of the FQDN is considered the best match. For instance,
if the lease address is "172.16.1.40" and there are two reverse domains in
the catalog: "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the
former is the best match. As with forward matching, it is possible to not
find a suitable match. Given the same two domains, there would be no
match for the lease address, "192.168.1.50", and the request would be
rejected. Finally, if there are no reverse DDNS Domains defined, D2 will
simply disregard the reverse update portion of requests.
</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dhcp-ddns-server-start-stop"></a>10.1. Starting and Stopping the DHCP-DDNS Server</h2></div></div></div><p>
<span class="command"><strong>kea-dhcp-ddns</strong></span> is the Kea DHCP-DDNS server
and, due to the nature of DDNS, it is run alongside either the
DHCPv4 or DHCPv6 components (or both). Like other parts of
Kea, it is a separate binary that can be run on its own or through
<span class="command"><strong>keactrl</strong></span> (see <a class="xref" href="#keactrl" title="Chapter 6. Managing Kea with keactrl">Chapter 6, <i>Managing Kea with keactrl</i></a>). In
normal operation, controlling <span class="command"><strong>kea-dhcp-ddns</strong></span>
with <span class="command"><strong>keactrl</strong></span> is recommended. However, it is also
possible to run the DHCP-DDNS server directly. It accepts the
following command-line switches:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>-c <em class="replaceable"><code>file</code></em></strong></span> -
specifies the configuration file. This is the only mandatory
switch.</li><li class="listitem">
<span class="command"><strong>-d</strong></span> - specifies whether the server
logging should be switched to debug/verbose mode. In verbose mode,
the logging severity and debuglevel specified in the configuration
file are ignored and "debug" severity and the maximum debuglevel
(99) are assumed. The flag is convenient, for temporarily
switching the server into maximum verbosity, e.g. when
debugging.</li><li class="listitem">
<span class="command"><strong>-v</strong></span> - prints out Kea version and exits.
</li><li class="listitem">
<span class="command"><strong>-V</strong></span> - prints out Kea extended version with
additional parameters and exits.
</li><li class="listitem">
<span class="command"><strong>-W</strong></span> - prints out Kea configuration report
and exits.
</li></ul></div><p>
The <span class="command"><strong>-V</strong></span> command returns the versions of the
external libraries dynamically linked.
</p><p>
The <span class="command"><strong>-W</strong></span> command describes the environment used
to build Kea. This command displays a copy of the
<code class="filename">config.report</code> file produced by
<strong class="userinput"><code>./configure</code></strong> that is embedded in the
executable binary.
</p><p>
The <code class="filename">config.report</code> may also be accessed more
directly. The following command may be used to extract this
information. The binary <strong class="userinput"><code>path</code></strong> may be found
in the install directory or in the <code class="filename">.libs</code>
subdirectory in the source tree. For example
<code class="filename">kea/src/bin/d2/.libs/kea-dhcp-ddns</code>.
</p><pre class="screen">
strings <strong class="userinput"><code>path</code></strong>/kea-dhcp-ddns | sed -n 's/;;;; //p'
</pre><p>
</p><p>
Upon start up the module will load its configuration and begin listening
for NCRs based on that configuration.
</p><p>
During startup the server will attempt to create a PID file of the
form: [localstatedir]/[conf name].kea-dhcp-ddns.pid
where:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>localstatedir</strong></span>: The value as passed into the
build configure script. It defaults to "/usr/local/var". Note
that this value may be overridden at run time by setting the environment
variable KEA_PIDFILE_DIR. This is intended primarily for testing purposes.
</li><li class="listitem"><span class="command"><strong>conf name</strong></span>: The configuration file name
used to start the server, minus all preceding path and file extension.
For example, given a pathname of "/usr/local/etc/kea/myconf.txt", the
portion used would be "myconf".
</li></ul></div><p>
If the file already exists and contains the PID of a live process,
the server will issue a DHCP_DDNS_ALREADY_RUNNING log message and exit. It
is possible, though unlikely, that the file is a remnant of a system crash
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="d2-configuration"></a>10.2. Configuring the DHCP-DDNS Server</h2></div></div></div><p>
Before starting <span class="command"><strong>kea-dhcp-ddns</strong></span> module for the
first time, a configuration file needs to be created. The following default
configuration is a template that can be customised to your requirements.
</p><pre class="screen">
<strong class="userinput"><code>"DhcpDdns": {
"ip-address": "127.0.0.1",
"port": 53001,
"dns-server-timeout": 100,
"ncr-protocol": "UDP",
"ncr-format": "JSON",
"tsig-keys": [ ],
"forward-ddns": {
"ddns-domains": [ ]
},
"reverse-ddns": {
"ddns-domains": [ ]
}
}</code></strong>
</pre><p>
</p><p>
The configuration can be divided as follows, each of which is described
in its own section:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>Global Server Parameters</strong></span> -
values which control connectivity and global server behavior
</li><li class="listitem">
<span class="command"><strong>TSIG Key Info</strong></span> -
defines the TSIG keys used for secure traffic with DNS servers
</li><li class="listitem">
<span class="command"><strong>Forward DDNS</strong></span> -
defines the catalog of Forward DDNS Domains
</li><li class="listitem">
<span class="command"><strong>Reverse DDNS</strong></span> -
defines the catalog of Forward DDNS Domains
</li></ul></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="d2-server-parameter-config"></a>10.2.1. Global Server Parameters</h3></div></div></div><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>ip-address</strong></span> - IP address on which D2
listens for requests. The default is the local loopback interface at
address 127.0.0.1. You may specify either an IPv4 or IPv6 address.
</li><li class="listitem">
<span class="command"><strong>port</strong></span> - Port on which D2 listens for requests. The default value
is 53001.
</li><li class="listitem">
<span class="command"><strong>dns-server-timeout</strong></span> - The maximum amount
of time in milliseconds, that D2 will wait for a response from a
DNS server to a single DNS update message.
</li><li class="listitem">
<span class="command"><strong>ncr-protocol</strong></span> - Socket protocol to use when sending requests to D2.
Currently only UDP is supported. TCP may be available in an upcoming
release.
</li><li class="listitem">
<span class="command"><strong>ncr-format</strong></span> - Packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be available
in future releases.
</li></ul></div><p>
D2 must listen for change requests on a known address and port. By
default it listens at 127.0.0.1 on port 53001. The following example
illustrates how to change D2's global parameters so it will listen
at 192.168.1.10 port 900:
</p><pre class="screen">
"DhcpDdns": {
<strong class="userinput"><code>"ip-address": "192.168.1.10",
"port": 900,</code></strong>
...
}
}</pre><p>
</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>
It is possible for a malicious attacker to send bogus
NameChangeRequests to the DHCP-DDNS server. Addresses
other than the IPv4 or IPv6 loopback addresses (127.0.0.1
or ::1) should only be used for testing purposes, but
note that local users may still communicate with the
DHCP-DDNS server. A future version of Kea will implement
authentication to guard against such attacks.
</p></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
If the ip-address and port are changed, it will be necessary to change the
corresponding values in the DHCP servers' "dhcp-ddns" configuration section.
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="d2-tsig-key-list-config"></a>10.2.2. TSIG Key List</h3></div></div></div><p>
A DDNS protocol exchange can be conducted with or without TSIG
(defined in <a class="ulink" href="http://tools.ietf/org/html/rfc2845" target="_top">RFC
2845</a>). This configuration section allows the administrator
to define the set of TSIG keys that may be used in such
exchanges.</p><p>To use TSIG when updating entries in a DNS Domain,
a key must be defined in the TSIG Key List and referenced by
name in that domain's configuration entry. When D2 matches a
change request to a domain, it checks whether the domain has
a TSIG key associated with it. If so, D2 will use that key to
sign DNS update messages sent to and verify responses received
from the domain's DNS server(s). For each TSIG key required by
the DNS servers that D2 will be working with there must be a
corresponding TSIG key in the TSIG Key list.</p><p>
As one might gather from the name, the tsig-key section of the
D2 configuration lists the TSIG keys. Each entry describes a
TSIG key used by one or more DNS servers to authenticate requests
and sign responses. Every entry in the list has three parameters:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>name</strong></span> -
a unique text label used to identify this key within the
list. This value is used to specify which key (if any) should be
used when updating a specific domain. So long as it is unique its
content is arbitrary, although for clarity and ease of maintenance
it is recommended that it match the name used on the DNS server(s).
It cannot be blank.
</li><li class="listitem">
<span class="command"><strong>algorithm</strong></span> -
specifies which hashing algorithm should be used with this
key. This value must specify the same algorithm used for the
key on the DNS server(s). The supported algorithms are listed below:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"><span class="command"><strong>HMAC-MD5</strong></span></li><li class="listitem"><span class="command"><strong>HMAC-SHA1</strong></span></li><li class="listitem"><span class="command"><strong>HMAC-SHA224</strong></span></li><li class="listitem"><span class="command"><strong>HMAC-SHA256</strong></span></li><li class="listitem"><span class="command"><strong>HMAC-SHA384</strong></span></li><li class="listitem"><span class="command"><strong>HMAC-SHA512</strong></span></li></ul></div>
This value is not case sensitive.
</li><li class="listitem">
<span class="command"><strong>digest-bits</strong></span> -
is used to specify the minimum truncated length in bits.
The default value 0 means truncation is forbidden, not 0
values must be an integral number of octets, be greater
than 80 and the half of the full length. Note in BIND9
this parameter is appended after a dash to the algorithm
name.
</li><li class="listitem">
<span class="command"><strong>secret</strong></span> -
is used to specify the shared secret key code for this key. This value is
case sensitive and must exactly match the value specified on the DNS server(s).
It is a base64-encoded text value.
</li></ul></div><p>
</p><p>
As an example, suppose that a domain D2 will be updating is
maintained by a BIND9 DNS server which requires dynamic updates
to be secured with TSIG. Suppose further that the entry for
the TSIG key in BIND9's named.conf file looks like this:
</p><pre class="screen">
:
key "key.four.example.com." {
algorithm hmac-sha224;
secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
};
:
</pre><p>
By default, the TSIG Key list is empty:
</p><pre class="screen">
"DhcpDdns": {
<strong class="userinput"><code>"tsig-keys": [ ]</code></strong>,
...
}
</pre><p>
We must extend the list with a new key:
</p><pre class="screen">
"DhcpDdns": {
"tsig-keys": [
<strong class="userinput"><code> {
"name": "key.four.example.com.",
"algorithm": "HMAC-SHA224",
"secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
}</code></strong>
],
...
}
</pre><p>
</p><p>These steps would be repeated for each TSIG key needed. Note that
the same TSIG key can be used with more than one domain.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="d2-forward-ddns-config"></a>10.2.3. Forward DDNS</h3></div></div></div><p>
The Forward DDNS section is used to configure D2's forward update
behavior. Currently it contains a single parameter, the catalog of
forward DDNS Domains, which is a list of structures.
</p><pre class="screen">
"DhcpDdns": {
<strong class="userinput"><code>"forward-ddns": {
"ddns-domains": [ ]
}</code></strong>,
...
}
</pre><p>
By default, this list is empty, which will cause the server to ignore
the forward update portions of requests.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="add-forward-ddns-domain"></a>10.2.3.1. Adding Forward DDNS Domains</h4></div></div></div><p>
A forward DDNS Domain maps a forward DNS zone to a set of
DNS servers which maintain the forward DNS data (i.e. name to
address mapping) for that zone. You will need one forward DDNS
Domain for each zone you wish to service. It may very well
be that some or all of your zones are maintained by the same
servers. You will still need one DDNS Domain per zone. Remember
that matching a request to the appropriate server(s) is done
by zone and a DDNS Domain only defines a single zone.
</p><p>
This section describes how to add Forward DDNS Domains. Repeat these
steps for each Forward DDNS Domain desired. Each Forward DDNS Domain
has the following parameters:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>name</strong></span> -
The fully qualified domain name (or zone) that this DDNS Domain
can update. This is value used to compare against the request
FQDN during forward matching. It must be unique within the
catalog.
</li><li class="listitem">
<span class="command"><strong>key-name</strong></span> -
If TSIG is used with this domain's servers, this
value should be the name of the key from within the TSIG Key List
to use. If the value is blank (the default), TSIG will not be
used in DDNS conversations with this domain's servers.
</li><li class="listitem">
<span class="command"><strong>dns-servers</strong></span> -
A list of one or more DNS servers which can conduct the server
side of the DDNS protocol for this domain. The servers
are used in a first to last preference. In other words, when D2
begins to process a request for this domain it will pick the
first server in this list and attempt to communicate with it.
If that attempt fails, it will move to next one in the list and
so on until the it achieves success or the list is exhausted.
</li></ul></div><p>
To create a new forward DDNS Domain, one must add a new domain
element and set its parameters:
</p><pre class="screen">
"DhcpDdns": {
"forward-ddns": {
"ddns-domains": [
<strong class="userinput"><code>{
"name": "other.example.com.",
"key-name": "",
"dns-servers": [
]
}</code></strong>
]
}
}
</pre><p>
It is permissible to add a domain without any servers. If that domain
should be matched to a request, however, the request will fail. In
order to make the domain useful though, we must add at least one DNS
server to it.
</p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="add-forward-dns-servers"></a>10.2.3.1.1. Adding Forward DNS Servers</h5></div></div></div><p>
This section describes how to add DNS servers to a Forward DDNS Domain.
Repeat them for as many servers as desired for a each domain.
</p><p>
Forward DNS Server entries represent actual DNS servers which
support the server side of the DDNS protocol. Each Forward DNS Server
has the following parameters:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>hostname</strong></span> -
The resolvable host name of the DNS server. This value is not
yet implemented.
</li><li class="listitem">
<span class="command"><strong>ip-address</strong></span> -
The IP address at which the server listens for DDNS requests.
This may be either an IPv4 or an IPv6 address.
</li><li class="listitem">
<span class="command"><strong>port</strong></span> -
The port on which the server listens for DDNS requests. It
defaults to the standard DNS service port of 53.
</li></ul></div><p>
To create a new forward DNS Server, one must add a new server
element to the domain and fill in its parameters. If for
example the service is running at "172.88.99.10", then set it as
follows:
</p><pre class="screen">
"DhcpDdns": {
"forward-ddns": {
"ddns-domains": [
{
"name": "other.example.com.",
"key-name": "",
"dns-servers": [
<strong class="userinput"><code>{
"hostname": "",
"ip-address": "172.88.99.10",
"port": 53
}</code></strong>
]
}
]
}
}
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
As stated earlier, "hostname" is not yet supported so, the parameter
"ip-address" must be set to the address of the DNS server.
</p></div></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="d2-reverse-ddns-config"></a>10.2.4. Reverse DDNS</h3></div></div></div><p>
The Reverse DDNS section is used to configure D2's reverse update
behavior, and the concepts are the same as for the forward DDNS
section. Currently it contains a single parameter, the catalog of
reverse DDNS Domains, which is a list of structures.
</p><pre class="screen">
"DhcpDdns": {
<strong class="userinput"><code>"reverse-ddns": {
"ddns-domains": [ ]
}</code></strong>
...
}
</pre><p>
By default, this list is empty, which will cause the server to ignore
the reverse update portions of requests.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="add-reverse-ddns-domain"></a>10.2.4.1. Adding Reverse DDNS Domains</h4></div></div></div><p>
A reverse DDNS Domain maps a reverse DNS zone to a set of DNS
servers which maintain the reverse DNS data (address to name
mapping) for that zone. You will need one reverse DDNS Domain
for each zone you wish to service. It may very well be that
some or all of your zones are maintained by the same servers;
even then, you will still need one DDNS Domain entry for each
zone. Remember that matching a request to the appropriate
server(s) is done by zone and a DDNS Domain only defines a
single zone.
</p><p>
This section describes how to add Reverse DDNS Domains. Repeat these
steps for each Reverse DDNS Domain desired. Each Reverse DDNS Domain
has the following parameters:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>name</strong></span> -
The fully qualified reverse zone that this DDNS Domain
can update. This is the value used during reverse matching
which will compare it with a reversed version of the request's
lease address. The zone name should follow the appropriate
standards: for example, to to support the IPv4 subnet 172.16.1,
the name should be. "1.16.172.in-addr.arpa.". Similarly,
to support an IPv6 subnet of 2001:db8:1, the name should be
"1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
Whatever the name, it must be unique within the catalog.
</li><li class="listitem">
<span class="command"><strong>key-name</strong></span> -
If TSIG should be used with this domain's servers, then this
value should be the name of that key from the TSIG Key List.
If the value is blank (the default), TSIG will not be
used in DDNS conversations with this domain's servers. Currently
this value is not used as TSIG has not been implemented.
</li><li class="listitem">
<span class="command"><strong>dns-servers</strong></span> -
a list of one or more DNS servers which can conduct the server
side of the DDNS protocol for this domain. Currently the servers
are used in a first to last preference. In other words, when D2
begins to process a request for this domain it will pick the
first server in this list and attempt to communicate with it.
If that attempt fails, it will move to next one in the list and
so on until the it achieves success or the list is exhausted.
</li></ul></div><p>
To create a new reverse DDNS Domain, one must add a new domain element
and set its parameters. For example, to support subnet 2001:db8:1::,
the following configuration could be used:
</p><pre class="screen">
"DhcpDdns": {
"reverse-ddns": {
"ddns-domains": [
<strong class="userinput"><code>{
"name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
"key-name": "",
"dns-servers": [
]
}</code></strong>
]
}
}
</pre><p>
It is permissible to add a domain without any servers. If that domain
should be matched to a request, however, the request will fail. In
order to make the domain useful though, we must add at least one DNS
server to it.
</p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="add-reverse-dns-servers"></a>10.2.4.1.1. Adding Reverse DNS Servers</h5></div></div></div><p>
This section describes how to add DNS servers to a Reverse DDNS Domain.
Repeat them for as many servers as desired for each domain.
</p><p>
Reverse DNS Server entries represents a actual DNS servers which
support the server side of the DDNS protocol. Each Reverse DNS Server
has the following parameters:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>hostname</strong></span> -
The resolvable host name of the DNS server. This value is
currently ignored.
</li><li class="listitem">
<span class="command"><strong>ip-address</strong></span> -
The IP address at which the server listens for DDNS requests.
</li><li class="listitem">
<span class="command"><strong>port</strong></span> -
The port on which the server listens for DDNS requests. It
defaults to the standard DNS service port of 53.
</li></ul></div><p>
To create a new reverse DNS Server, one must first add a new server
element to the domain and fill in its parameters. If for
example the service is running at "172.88.99.10", then set it as
follows:
</p><pre class="screen">
"DhcpDdns": {
"reverse-ddns": {
"ddns-domains": [
{
"name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
"key-name": "",
"dns-servers": [
<strong class="userinput"><code>{
"hostname": "",
"ip-address": "172.88.99.10",
"port": 53
}</code></strong>
]
}
]
}
}
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
As stated earlier, "hostname" is not yet supported so, the parameter
"ip-address" must be set to the address of the DNS server.
</p></div></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="d2-exmaple-config"></a>10.2.5. Example DHCP-DDNS Server Configuration</h3></div></div></div><p>
This section provides an example DHCP-DDNS server configuration based
on a small example network. Let's suppose our example network has
three domains, each with their own subnet.
</p><div class="table"><a name="idp55451472"></a><p class="title"><b>Table 10.1. Our example network</b></p><div class="table-contents"><table summary="Our example network" border="1"><colgroup><col align="left" class="domain"><col align="left" class="subnet"><col align="left" class="fservers"><col align="left" class="rservers"></colgroup><thead><tr><th align="left">Domain</th><th align="left">Subnet</th><th align="left">Forward DNS Servers</th><th align="left">Reverse DNS Servers</th></tr></thead><tbody><tr><td align="left">four.example.com</td><td align="left">192.0.2.0/24</td><td align="left">172.16.1.5, 172.16.2.5</td><td align="left">172.16.1.5, 172.16.2.5</td></tr><tr><td align="left">six.example.com</td><td align="left">2001:db8:1::/64</td><td align="left">3001:1::50</td><td align="left">3001:1::51</td></tr><tr><td align="left">example.com</td><td align="left">192.0.0.0/16</td><td align="left">172.16.2.5</td><td align="left">172.16.2.5</td></tr></tbody></table></div></div><p><br class="table-break">
</p><p>
We need to construct three forward DDNS Domains:
</p><div class="table"><a name="idp55465872"></a><p class="title"><b>Table 10.2. Forward DDNS Domains Needed</b></p><div class="table-contents"><table summary="Forward DDNS Domains Needed" border="1"><colgroup><col align="left" class="num"><col align="left" class="name"><col align="left" class="servers"></colgroup><thead><tr><th align="left">#</th><th align="left">DDNS Domain Name</th><th align="left">DNS Servers</th></tr></thead><tbody><tr><td align="left">1.</td><td align="left">four.example.com.</td><td align="left">172.16.1.5, 172.16.2.5</td></tr><tr><td align="left">2.</td><td align="left">six.example.com.</td><td align="left">3001:1::50</td></tr><tr><td align="left">3.</td><td align="left">example.com.</td><td align="left">172.16.2.5</td></tr></tbody></table></div></div><p><br class="table-break">
As discussed earlier, FQDN to domain matching is based on the longest
match. The FQDN, "myhost.four.example.com.", will match the first
domain ("four.example.com") while "admin.example.com." will match the
third domain ("example.com"). The
FQDN, "other.example.net." will fail to match any domain and would
be rejected.
</p><p>
The following example configuration specified the Forward DDNS Domains.
</p><pre class="screen"><strong class="userinput"><code>
"DhcpDdns": {
"forward-ddns": {
"ddns-domains": [
{
"name": "four.example.com.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.1.5" },
{ "ip-address": "172.16.2.5" }
]
},
{
"name": "six.example.com.",
"key-name": "",
"dns-servers": [
{ "ip-address": "2001:db8::1" }
]
},
{
"name": "example.com.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.2.5" }
]
},
]
}
}</code></strong>
</pre><p>
</p><p>
Similarly, we need to construct the three reverse DDNS Domains:
</p><div class="table"><a name="idp55480416"></a><p class="title"><b>Table 10.3. Reverse DDNS Domains Needed</b></p><div class="table-contents"><table summary="Reverse DDNS Domains Needed" border="1"><colgroup><col align="left" class="num"><col align="left" class="DDNS Domain name"><col align="left" class="DDNS Domain DNS Servers"></colgroup><thead><tr><th align="left">#</th><th align="left">DDNS Domain Name</th><th align="left">DNS Servers</th></tr></thead><tbody><tr><td align="left">1.</td><td align="left">2.0.192.in-addr.arpa.</td><td align="left">172.16.1.5, 172.16.2.5</td></tr><tr><td align="left">2.</td><td align="left">1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa.</td><td align="left">3001:1::50</td></tr><tr><td align="left">3.</td><td align="left">0.182.in-addr.arpa.</td><td align="left">172.16.2.5</td></tr></tbody></table></div></div><p><br class="table-break">
An address of "192.0.2.150" will match the first domain,
"2001:db8:1::10" will match the second domain, and "192.0.50.77"
the third domain.
</p><p>
These Reverse DDNS Domains are specified as follows:
</p><pre class="screen"><strong class="userinput"><code>
"DhcpDdns": {
"reverse-ddns": {
"ddns-domains": [
{
"name": "2.0.192.in-addr.arpa.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.1.5" },
{ "ip-address": "172.16.2.5" }
]
}
{
"name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
"key-name": "",
"dns-servers": [
{ "ip-address": "2001:db8::1" }
]
}
{
"name": "0.192.in-addr.arpa.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.2.5" }
]
}
]
}
}</code></strong>
</pre><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp55495520"></a>10.3. DHCP-DDNS Server Limitations</h2></div></div></div><p>The following are the current limitations of the DHCP-DDNS Server.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
Requests received from the DHCP servers are placed in a
queue until they are processed. Currently all queued requests
are lost when the server shuts down.
</li></ul></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="kea-lfc"></a>Chapter 11. The LFC process</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#kea-lfc-overview">11.1. Overview</a></span></dt><dt><span class="section"><a href="#kea-lfc-usage">11.2. Command Line Options</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kea-lfc-overview"></a>11.1. Overview</h2></div></div></div><p><span class="command"><strong>kea-lfc</strong></span> is a service process that removes
redundant information from the files used to provide persistent storage
for the memfile data base backend. This service is written to run as a
stand alone process.
</p><p>While <span class="command"><strong>kea-lfc</strong></span> can be started externally, there is
usually no need to do this. <span class="command"><strong>kea-lfc</strong></span> is run on a periodic
basis by the Kea DHCP servers.
</p><p>The process operates on a set of files, using them for input and output
of the lease entries and to indicate where it is in the process in case of an
interruption. Currently the caller must supply names for all of the files, in
the future this requirement may be relaxed with the process getting the names
from either the config file or from defaults.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kea-lfc-usage"></a>11.2. Command Line Options</h2></div></div></div><p><span class="command"><strong>kea-lfc</strong></span> is run as follows:
</p><pre class="screen">
kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file
</pre><p>
</p><p>The argument <span class="command"><strong>-4</strong></span> or <span class="command"><strong>-6</strong></span> selects the protocol
version of the lease files.
</p><p>The <span class="command"><strong>-c</strong></span> argument specifies the configuration file. This is
required, but not currently used by the process.
</p><p>The <span class="command"><strong>-p</strong></span> argument specifies the PID file. When the
<span class="command"><strong>kea-lfc</strong></span> process starts it attempts to determine if another
instance of the process is already running by examining the pid file. If one
is already running the new process is terminated. If one isn't running it writes
its pid into the pid file.
</p><p>The other filenames specify where the <span class="command"><strong>kea-lfc</strong></span> process
should look for input, write its output and use for bookkeeping.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
<span class="command"><strong>previous</strong></span> —
When <span class="command"><strong>kea-lfc</strong></span> starts this
is the result of any previous run of <span class="command"><strong>kea-lfc</strong></span>.
When <span class="command"><strong>kea-lfc</strong></span> finishes it is the result of this run.
If <span class="command"><strong>kea-lfc</strong></span> is interrupted before completing,
this file may not exist.
</li><li class="listitem">
<span class="command"><strong>input</strong></span> —
Before the DHCP server invokes <span class="command"><strong>kea-lfc</strong></span> it will
move the current lease file here and then call <span class="command"><strong>kea-lfc</strong></span>
with this file.
</li><li class="listitem">
<span class="command"><strong>output</strong></span> —
The temporary file <span class="command"><strong>kea-lfc</strong></span> should use to write the leases.
Upon completion of writing this file, it will be moved to the finish file
(see below).
</li><li class="listitem">
<span class="command"><strong>finish</strong></span> —
Another temporary file <span class="command"><strong>kea-lfc</strong></span> uses for bookkeeping. When
<span class="command"><strong>kea-lfc</strong></span> completes writing the outputfile it moves it to this
file name. After <span class="command"><strong>kea-lfc</strong></span> finishes deleting the other files
(previous and input) it moves this file to previous lease file. By moving the
files in this fashion the <span class="command"><strong>kea-lfc</strong></span> and the DHCP server
processes can determine the correct file to use even if one of the
processes was interrupted before completing its task.
</li></ul></div><p>
</p><p>There are several additional arguments mostly for debugging purposes.
<span class="command"><strong>-d</strong></span> Sets the logging level to debug. <span class="command"><strong>-v</strong></span> and
<span class="command"><strong>-V</strong></span> print out version stamps with <span class="command"><strong>-V</strong></span> providing
a longer form. <span class="command"><strong>-h</strong></span> prints out the usage string.
</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="classify"></a>Chapter 12. Client Classification</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idp49591728">12.1. Client Classification Overview</a></span></dt><dt><span class="section"><a href="#classification-using-vendor">12.2. Using Vendor Class Information In Classification</a></span></dt><dt><span class="section"><a href="#classification-using-expressions">12.3. Using Expressions In Classification</a></span></dt><dd><dl><dt><span class="section"><a href="#idp55587760">12.3.1. Substring</a></span></dt></dl></dd><dt><span class="section"><a href="#classification-configuring">12.4. Configuring Classes</a></span></dt><dt><span class="section"><a href="#classification-subnets">12.5. Configuring Subnets With Class Information</a></span></dt><dt><span class="section"><a href="#idp55504128">12.6. Using Classes</a></span></dt><dt><span class="section"><a href="#idp55506384">12.7. Classes and Hooks</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp49591728"></a>12.1. Client Classification Overview</h2></div></div></div><p>
In certain cases it is useful to differentiate between different
types of clients and treat them accordingly. Common reasons include:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
The clients represent different pieces of topology, e.g. a cable
modem is different to the clients behind that modem.
</p></li><li class="listitem"><p>
The clients have different behavior, e.g. a smart phone behaves
differently to a laptop.
</p></li><li class="listitem"><p>
The clients require different values for some options, e.g. a docsis3.0
cable modem requires different settings to docsis2.0 cable modem.
</p></li></ul></div><p>
</p><p>
It is envisaged that client classification will be used for changing the
behavior of almost any part of the DHCP message processing, including the assignment of
leases from different pools, the assignment of different options (or different values of
the same options) etc. In the current release of the software however, there are
only three mechanisms that take
advantage of client classification: subnet selection, assignment of different
options and, for DHCPv4 cable modems, the setting of specific options for use with
the TFTP server address and the boot file field.
</p><p>
The process of doing classification is conducted in three steps:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Assess an incoming packet and assign it to zero or more classes.
</p></li><li class="listitem"><p>
Choose a subnet, possibly based on the class information.
</p></li><li class="listitem"><p>
Assign options, again possibly based on the class information.
</p></li></ol></div><p>
</p><p>
When determining which options to include in the response the server will examine
the union of options from all of the assigned classes. In the case two or more
classes include the same option, the value from the first class examined will
be used. When choosing a subnet the server will iterate over all of the
subnets that are feasible given the information found in the packet (client address,
relay address etc). It will use the first subnet it finds that either doesn't
have a class associated with it or that has a class which matches one of
the packet's classes. In the future the processing order of the
various classes may be specified but for now it is being left unspecified and
may change in future releases.
</p><p>
As an example, imagine two classes. Class "foo" defines values for an NTP server
(option 42 in DHCPv4) and an SMTP server (option 69 in DHCPv4) while class
"bar" defines values for an NTP server and a POP3 server (option 70 in DHCPv4).
The server will examine the three options NTP, SMTP and POP3 and return any
of them that the client requested. As the NTP server was defined twice the
server will choose only one of the values for the reply: the class from which the
value is obtained is unspecified.
</p><p>
There are two methods of doing classification. The first is automatic and relies
on examining the values in the vendor class options. Information from these
options is extracted and a class name is constructed from it and added to
the class list for the packet. The second allows you to specify an expression
that is evaluated for each packet. If the result is true, the packet is
a member of the class.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Care should be taken with client classification as it is easy for
clients that do not meet class criteria to be denied any service altogether.
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="classification-using-vendor"></a>12.2. Using Vendor Class Information In Classification</h2></div></div></div><p>
The server checks whether an incoming DHCPv4 packet includes
the vendor class identifier option (60) or an incoming DHCPv6 packet
includes the vendor class option (16). If it does, the content of that
option is prepended with "VENDOR_CLASS_" and the result is interpreted
as a class. For example, modern cable modems will send this option with
value "docsis3.0" and so the packet will belong to
class "VENDOR_CLASS_docsis3.0".
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="classification-using-expressions"></a>12.3. Using Expressions In Classification</h2></div></div></div><p>
The expression portion of classification contains operators and values.
All values are currently strings and operators take a string or strings and
return another string. When all the operations have completed
the result should be a value of "true" or "false".
The packet belongs to
the class (and the class name is added to the list of classes) if the result
is "true". Expressions are written in standard format and can be nested.
</p><p>
Expressions are pre-processed during the parsing of the configuration file
and converted to an internal representation. This allows certain types of
errors to be caught and logged during parsing. Examples of these errors
include incorrect number or types of arguments to an operator. The
evaluation code will also check for this class of error and generally
throw an exception, though they should not occur in a normally functioning
system.
</p><p>
Other issues, for example the starting position of a substring being
outside of the substring or an option not existing in the packet, result
in the operator returning an empty string.
</p><p>
Expressions are a work in progress and the supported operators and
values are limited. The expectation is that additional operators and values
will be added over time, however it is expected the basic mechanisms will
remain the same.
</p><p>
</p><div class="table"><a name="classification-values-list"></a><p class="title"><b>Table 12.1. List of Classification Values</b></p><div class="table-contents"><table summary="List of Classification Values" border="1"><colgroup><col class="name"><col class="example"><col class="description"></colgroup><thead><tr><th>Name</th><th>Example</th><th>Description</th></tr></thead><tbody><tr><td>String</td><td>'example'</td><td>A string</td></tr><tr><td>Hex String</td><td>0XABCD</td><td>A hexadecimal string</td></tr><tr><td>Integer</td><td>123</td><td>An integer value</td></tr><tr><td>Option Hex</td><td>option[code].hex</td><td>The value of the option with code "code" from the packet as hex</td></tr></tbody></table></div></div><p><br class="table-break">
Hex Strings are converted into a string as expected. The starting "0X" or
"0x" is removed and if the string is an odd number of characters a
"0" is prepended to it.
</p><p>
Integers in the expression are converted to strings
when the expression is read into Kea.
</p><p>
"option[code].hex" extracts the value of the option with the given code
from the incoming packet. If the packet doesn't contain the option, it
returns the empty string. The string is presented as a byte string of
the option payload without the type code or length fields.
</p><p>
</p><div class="table"><a name="classification-expressions-list"></a><p class="title"><b>Table 12.2. List of Classification Expressions</b></p><div class="table-contents"><table summary="List of Classification Expressions" border="1"><colgroup><col class="name"><col class="example"><col class="description"></colgroup><thead><tr><th>Name</th><th>Example</th><th>Description</th></tr></thead><tbody><tr><td>Equal</td><td>'foo' == 'bar'</td><td>Compare the two values and return "true" or "false"</td></tr><tr><td>Substring</td><td>substring('foobar',0,3)</td><td>Return the requested substring</td></tr></tbody></table></div></div><p><br class="table-break">
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp55587760"></a>12.3.1. Substring</h3></div></div></div>
The substring operator "substring(value, start, length)" accepts both positive and
negative values for the starting position and the length. For "start", a value of
0 is the first byte in the string while -1 is the last byte. If the starting
point is outside of the original string an empty string is returned. "length"
is the number of bytes to extract. A negative number means to count towards
the beginning of the string but doesn't include the byte pointed to by "start".
The special value "all" means to return all bytes from start to the end of the
string. If length is longer than the remaining portion of the string then
the entire remaining portion is returned. Some examples may be helpful:
<pre class="screen">
substring('foobar', 0, 6) == 'foobar'
substring('foobar', 3, 3) == 'bar'
substring('foobar', 3, all) == 'bar'
substring('foobar', 1, 4) == 'ooba'
substring('foobar', -5, 4) == 'ooba'
substring('foobar', -1, -3) == 'oba'
substring('foobar', 4, -2) == 'ob'
substring('foobar', 10, 2) == ''
</pre></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
The expression for each class is executed on each packet received.
If the expressions are overly complex, the time taken to execute
them may impact the performance of the server. If you need
complex or time consuming expressions you should write a <a class="link" href="#hooks-libraries" title="Chapter 13. Hooks Libraries">hook</a> to perform the necessary work.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="classification-configuring"></a>12.4. Configuring Classes</h2></div></div></div><p>
A class contains three items: a name, a test expression and option data.
The name must exist and must be unique amongst all classes. The test
expression and option data are optional.
</p><p>
The test expression is a string containing the logical expression used to
determine membership in the class. The entire expression is in double
quotes.
</p><p>
The option data is a list which defines any options that should be assigned
to members of this class.
</p><p>
In the following example the class named "Client_foo" is defined.
It is comprised of all clients who's client ids (option 61) start with the
string "foo". Members of this class will be given 192.0.2.1 and
192.0.2.2 as their domain name servers.
</p><pre class="screen">
"Dhcp4": {
"client-classes": [<strong class="userinput"><code>
{
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]
},
...
],</code></strong>
...
}</pre><p>
</p><p>
This example shows a client class being defined for use by the DHCPv6 server.
In it the class named "Client_enterprise" is defined. It is comprised
of all clients who's client identifiers start with the given hex string (which
would indicate a DUID based on an enterprise id of 0xAABBCCDD). Members of this
class will be given an 2001:db8:0::1 and 2001:db8:2::1 as their domain name servers.
</p><pre class="screen">
"Dhcp6": {
"client-classes": [<strong class="userinput"><code>
{
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]
},
...
],</code></strong>
...
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="classification-subnets"></a>12.5. Configuring Subnets With Class Information</h2></div></div></div><p>
In certain cases it beneficial to restrict access to certain subnets
only to clients that belong to a given class using the "client-class"
keyword when defining the subnet.
</p><p>
Let's assume that the server is connected to a network segment that uses
the 192.0.2.0/24 prefix. The Administrator of that network has decided
that addresses from range 192.0.2.10 to 192.0.2.20 are going to be
managed by the DHCP4 server. Only clients belonging to client class
Client_foo are allowed to use this subnet. Such a
configuration can be achieved in the following way:
</p><pre class="screen">
"Dhcp4": {
"client-classes": [
{
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]
},
...
],<strong class="userinput"><code>
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"client-class": "Client_foo"
},
...
],</code></strong>,
...
}</pre><p>
</p><p>
The following example shows restricting access to a DHCPv6 subnet. This
configuration will restrict use of the addresses 2001:db8:1::1 to
2001:db8:1::FFFF to members of the "Client_enterprise" class.
</p><pre class="screen">
"Dhcp6": {
"client-classes": [
{
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]
},
...
], <strong class="userinput"><code>
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
"client-class": "Client_enterprise"
}
],</code></strong>
...
}</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp55504128"></a>12.6. Using Classes</h2></div></div></div><p>
Currently classes can be used for two functions. They can supply options
to the members of the class and they can be used to choose a subnet from which an
address will be assigned to the class member.
</p><p>
When supplying options, options defined as part of the class definition
are considered "class globals". They will override any global options that
may be defined and in turn will be overridden by any options defined for an
individual subnet.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp55506384"></a>12.7. Classes and Hooks</h2></div></div></div><p>
You may use a hook to classify your packets. This may be useful if the
expression would either be complex or time consuming and be easier or
better to write as code. Once the hook has added the proper class name
to the packet the rest of the classification system will work as normal
in choosing a subnet and selecting options. For a description of the
hooks see <a class="xref" href="#hooks-libraries" title="Chapter 13. Hooks Libraries">Chapter 13, <i>Hooks Libraries</i></a>, for a description on
configuring he classes see <a class="xref" href="#classification-configuring" title="12.4. Configuring Classes">Section 12.4, “Configuring Classes”</a>
and <a class="xref" href="#classification-subnets" title="12.5. Configuring Subnets With Class Information">Section 12.5, “Configuring Subnets With Class Information”</a>.
</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="hooks-libraries"></a>Chapter 13. Hooks Libraries</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#hooks-libraries-introduction">13.1. Introduction</a></span></dt><dt><span class="section"><a href="#idp52289920">13.2. Configuring Hooks Libraries</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="hooks-libraries-introduction"></a>13.1. Introduction</h2></div></div></div><p>
Although Kea offers a lot of flexibility, there may be cases where
its behavior needs customisation. To accommodate this possibility,
Kea includes the idea of "Hooks". This feature lets Kea load one
or more dynamically-linked libraries (known as "hooks libraries")
and, at various points in its processing ("hook points"), call
functions in them. Those functions perform whatever custom
processing is required.
</p><p>
Hooks libraries are attached to individual Kea processes, not to
Kea as a whole. This means (for example) that it is possible
to associate one set of libraries with the DHCP4 server and a
different set to the DHCP6 server.
</p><p>
Another point to note is that it is possible for a process to
load multiple libraries. When processing reaches a hook point,
Kea calls the hooks library functions attached to it. If multiple
libraries have attached a function to a given hook point, Kea calls
all of them, in the order in which the libraries are specified in
the configuration file. The order may be important: consult the
documentation of the libraries to see if this is the case.
</p><p>
The next section describes how to configure hooks libraries. If you
are interested in writing your own hooks library, information can be
found in the <a class="ulink" href="http://git.kea.isc.org/~tester/kea/doxygen" target="_top">Kea
Developer's Guide</a>.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp52289920"></a>13.2. Configuring Hooks Libraries</h2></div></div></div><p>
The hooks libraries for a given process are configured using the
<span class="command"><strong>hooks-libraries</strong></span> keyword in the
configuration for that process. (Note that
the word "hooks" is plural). The value of the keyword
is an array of map structures, each structure corresponding to a hooks
library. For example, to set up two hooks libraries for the DHCPv4
server, the configuration would be:
</p><pre class="screen">
<strong class="userinput"><code>"Dhcp4": {
:
"hooks-libraries": [
{
"library": "/opt/charging.so"
},
{
"library": "/opt/local/notification.so"
}
]
:
}</code></strong>
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
This is a change to the syntax used in Kea 0.9.2 and earlier, where
hooks-libraries was a list of strings, each string being the name of
a library. The change has been made in Kea 1.0 to facilitate the
specification of library-specific parameters, a feature that will be
added to a future version of Kea.
</p></div><p>
Notes:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>
The full path to each library should be given.
</p></li><li class="listitem" style="list-style-type: disc"><p>
As noted above, order may be important - consult the documentation for
each library.
</p></li><li class="listitem" style="list-style-type: disc"><p>
An empty list has the same effect as omitting the
<span class="command"><strong>hooks-libraries</strong></span> configuration element all together.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
There is one case where this is not true: if Kea
is running with a configuration that contains a
<span class="command"><strong>hooks-libraries</strong></span> item, and that item is
removed and the configuration reloaded, the removal will be
ignored and the libraries remain loaded. As a workaround,
instead of removing the <span class="command"><strong>hooks-libraries</strong></span>
item, change it to an empty list. This will be fixed in a
future version of Kea.
</p></div></li></ul></div><p>
</p><p>
At the present time, only the kea-dhcp4 and kea-dhcp6 processes support
hooks libraries.
</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="stats"></a>Chapter 14. Statistics</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idp54285232">14.1. Statistics Overview</a></span></dt><dt><span class="section"><a href="#stats-lifecycle">14.2. Statistics Lifecycle</a></span></dt><dt><span class="section"><a href="#command-stats">14.3. Commands for Manipulating Statistics</a></span></dt><dd><dl><dt><span class="section"><a href="#command-statistic-get">14.3.1. statistic-get command</a></span></dt><dt><span class="section"><a href="#command-statistic-reset">14.3.2. statistic-reset command</a></span></dt><dt><span class="section"><a href="#command-statistic-remove">14.3.3. statistic-remove command</a></span></dt><dt><span class="section"><a href="#command-statistic-get-all">14.3.4. statistic-get-all command</a></span></dt><dt><span class="section"><a href="#command-statistic-reset-all">14.3.5. statistic-reset-all command</a></span></dt><dt><span class="section"><a href="#command-statistic-remove-all">14.3.6. statistic-remove-all command</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp54285232"></a>14.1. Statistics Overview</h2></div></div></div><p>Both Kea DHCP servers support statistics gathering since
0.9.2-beta version. A working DHCP server encounters various events
that can cause certain statistics to be collected. For
example, a DHCPv4 server may receive a packet (pkt4-received
statistic increases by one) that after parsing was identifier as
DHCPDISCOVER (pkt4-discover-received). The Server processed it and
decided to send DHCPOFFER representing its answer (pkt4-offer-sent
and pkt4-sent statistics increase by one). Such events happen
frequently, so it is not uncommon for the statistics to have
values in high thousands. They can serve as an easy and powerful
tool for observing a server's and network's health. For example,
if pkt4-received statistic stops growing, it means that the
clients' packets are not reaching the server.</p><p>There are four types of statistics:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="emphasis"><em>integer</em></span> - this is the most common type. It
is implemented as 64 bit integer (int64_t in C++), so it can hold any
value between -2^63 to 2^63 -1.</li><li class="listitem"><span class="emphasis"><em>floating point</em></span> - this type is intended to
store floating point precision. It is implemented as double C++ type.
</li><li class="listitem"><span class="emphasis"><em>duration</em></span> - this type is intended for
recording time periods. It uses boost::posix_time::time_duration type,
which stores hours, minutes, seconds and microseconds.</li><li class="listitem"><span class="emphasis"><em>string</em></span> - this type is intended for
recording statistics in textual form. It uses std::string C++ type.
</li></ul></div><p>
</p><p>
During normal operation, DHCPv4 and DHCPv6 servers gather statistics.
For a list of DHCPv4 and DHCPv6 statistics, see <a class="xref" href="#dhcp4-stats" title="7.7. Statistics in DHCPv4 server">Section 7.7, “Statistics in DHCPv4 server”</a> and <a class="xref" href="#dhcp6-stats" title="8.11. Statistics in DHCPv6 server">Section 8.11, “Statistics in DHCPv6 server”</a>, respectively.
</p><p>
To extract data from the statistics module, the control channel can be
used. See <a class="xref" href="#ctrl-channel" title="Chapter 15. Management API">Chapter 15, <i>Management API</i></a> for details. It is possible to
retrieve a single or all statistics, reset statistics (i.e. set to neutral
value, typically zero) or even remove completely a single or all
statistics. See section <a class="xref" href="#command-stats" title="14.3. Commands for Manipulating Statistics">Section 14.3, “Commands for Manipulating Statistics”</a> for a list of
statistic oriented commands.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="stats-lifecycle"></a>14.2. Statistics Lifecycle</h2></div></div></div><p>
It is useful to understand how the Statistics Manager module works. When
the server starts operation, the manager is empty and does not have any
statistics. When <span class="command"><strong>statistic-get-all</strong></span> is executed, an
empty list is returned. Once the server performs an operation that causes
a statistic to change, the related statistic will be created. In the general
case once a statistic is recorded even once, it is kept in the manager, until
explicitly removed, by <span class="command"><strong>statistic-remove</strong></span> or
<span class="command"><strong>statistic-remove-all</strong></span> being called or the server is shut
down. Per subnet statistics are explicitly removed when reconfiguration
takes place.
</p><p>
Statistics are considered run-time properties, so they are not retained
after server restart.
</p><p>
Removing a statistic that is updated frequently makes little sense as it
will be re-added when the server code next records that statistic.
The <span class="command"><strong>statistic-remove</strong></span> and
<span class="command"><strong>statistic-remove-all</strong></span> commands are intended to remove
statistics that are not expected to be observed in the near future. For
example, a misconfigured device in a network may cause clients to report
duplicate addresses, so the server will report increasing values of
pkt4-decline-received. Once the problem is found and the device is
removed, the system administrator may want to remove the
pkt4-decline-received statistic, so it won't be reported anymore. If a
duplicate address is detected ever again, the server will add this
statistic back.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="command-stats"></a>14.3. Commands for Manipulating Statistics</h2></div></div></div><p>
There are several commands defined that can be used for accessing (-get),
resetting to zero or neutral value (-reset) or even removing a statistic
completely (-remove). The difference between reset and remove is somewhat
subtle. The reset command sets the value of the statistic to zero or neutral
value. After this operation, the statistic will have a value of 0 (integer),
0.0 (float), 0h0m0s0us (duration) or "" (string). When asked for, a statistic
with the values mentioned will be returned. <span class="command"><strong>Remove</strong></span> removes
a statistic completely, so the statistic will not be reported anymore. Please
note that the server code may add it back if there's a reason to record
it.
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-statistic-get"></a>14.3.1. statistic-get command</h3></div></div></div><p>
<span class="emphasis"><em>statistic-get</em></span> command retrieves a single
statistic. It takes a single string parameter called
<span class="command"><strong>name</strong></span> that specifies the statistic name. An example
command may look like this:
</p><pre class="screen">
{
"command": "statistic-get",
"arguments": {
"name": "<strong class="userinput"><code>pkt4-received</code></strong>"
}
}
</pre><p>
</p><p>
The server will respond with details of the requested statistic, with result
set to 0 indicating success and the specified statistic as the value of
"arguments" parameter. If the requested statistic is not found, the response
will contain an empty map, i.e. only { } as argument, but the status
code will still be set to success (0).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-statistic-reset"></a>14.3.2. statistic-reset command</h3></div></div></div><p>
<span class="emphasis"><em>statistic-reset</em></span> command sets the specified statistic
to its neutral value: 0 for integer, 0.0 for float, 0h0m0s0us for time
duration and "" for string type. It takes a single string parameter
called <span class="command"><strong>name</strong></span> that specifies the statistic name. An
example command may look like this:
</p><pre class="screen">
{
"command": "statistic-reset",
"arguments": {
"name": "<strong class="userinput"><code>pkt4-received</code></strong>"
}
}
</pre><p>
</p><p>
If the specific statistic is found and reset was successful, the
server will respond with a status of 0, indicating success and an empty
parameters field. If an error is encountered (e.g. requested statistic
was not found), the server will return a status code of 1 (error)
and the text field will contain the error description.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-statistic-remove"></a>14.3.3. statistic-remove command</h3></div></div></div><p>
<span class="emphasis"><em>statistic-remove</em></span> command attempts to delete a single
statistic. It takes a single string parameter called
<span class="command"><strong>name</strong></span> that specifies the statistic name. An example
command may look like this:
</p><pre class="screen">
{
"command": "statistic-remove",
"arguments": {
"name": "<strong class="userinput"><code>pkt4-received</code></strong>"
}
}
</pre><p>
</p><p>
If the specific statistic is found and its removal was successful, the
server will respond with a status of 0, indicating success and an empty
parameters field. If an error is encountered (e.g. requested statistic
was not found), the server will return a status code of 1 (error)
and the text field will contain the error description.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-statistic-get-all"></a>14.3.4. statistic-get-all command</h3></div></div></div><p>
<span class="emphasis"><em>statistic-get-all</em></span> command retrieves all statistics
recorded. An example command may look like this:
</p><pre class="screen">
{
"command": "statistic-get-all",
"arguments": { }
}
</pre><p>
</p><p>
The server will respond with details of all recorded statistics, with result
set to 0 indicating that it iterated over all statistics (even when
the total number of statistics is zero).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-statistic-reset-all"></a>14.3.5. statistic-reset-all command</h3></div></div></div><p>
<span class="emphasis"><em>statistic-reset</em></span> command sets all statistics to
their neutral values: 0 for integer, 0.0 for float, 0h0m0s0us for time
duration and "" for string type. An example command may look like this:
</p><pre class="screen">
{
"command": "statistic-reset-all",
"arguments": { }
}
</pre><p>
</p><p>
If the operation is successful, the server will respond with a status of
0, indicating success and an empty parameters field. If an error is
encountered, the server will return a status code of 1 (error) and the text
field will contain the error description.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-statistic-remove-all"></a>14.3.6. statistic-remove-all command</h3></div></div></div><p>
<span class="emphasis"><em>statistic-remove-all</em></span> command attempts to delete all
statistics. An example command may look like this:
</p><pre class="screen">
{
"command": "statistic-remove-all",
"arguments": { }
}
</pre><p>
</p><p>
If the removal of all statistics was successful, the server will respond
with a status of 0, indicating success and an empty parameters field. If
an error is encountered, the server will return a status code of 1 (error)
and the text field will contain the error description.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="ctrl-channel"></a>Chapter 15. Management API</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#ctrl-channel-syntax">15.1. Data syntax</a></span></dt><dt><span class="section"><a href="#ctrl-channel-client">15.2. Using control channel</a></span></dt><dt><span class="section"><a href="#commands-common">15.3. Commands supported by both DHCPv4 and DHCPv6 servers</a></span></dt><dd><dl><dt><span class="section"><a href="#command-leases-reclaim">15.3.1. leases-reclaim command</a></span></dt><dt><span class="section"><a href="#command-list-commands">15.3.2. list-commands command</a></span></dt><dt><span class="section"><a href="#command-shutdown">15.3.3. shutdown command</a></span></dt></dl></dd></dl></div><p>A classic approach to daemon configuration assumes that
the server's configuration is stored in the configuration files
and when the configuration is changed, the daemon is restarted.
This approach has the significant disadvantage of introducing periods
of downtime, when client traffic is not handled. Another risk
is that if the new configuration is invalid for whatever reason,
the server may refuse to start, which will further extend the
downtime period, until the issue is resolved.</p><p>To avoid such problems, both DHCPv4 and DHCPv6 servers
introduced support for a mechanism that will allow
on-line reconfiguration, without requiring server shutdown.
Both servers can be instructed to open control sockets, which
is a communication channel. The server is able to receive
commands on that channel, act on them and report back status.
While the set of commands supported in Kea 0.9.2 is limited,
the number is expected to grow over time.</p><p>Currently the only supported type of control channel
is UNIX stream socket. For details how to configure it, see
<a class="xref" href="#dhcp4-ctrl-channel" title="7.8. Management API for the DHCPv4 server">Section 7.8, “Management API for the DHCPv4 server”</a> and <a class="xref" href="#dhcp6-ctrl-channel" title="8.12. Management API for the DHCPv6 server">Section 8.12, “Management API for the DHCPv6 server”</a>. It is likely that support
for other control channel types will be added in the future.
</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ctrl-channel-syntax"></a>15.1. Data syntax</h2></div></div></div><p>Communication over control channel is conducted using JSON
structures. If configured, Kea will open a socket and will listen
for any incoming connections. A process connecting to this socket
is expected to send JSON commands structured as follows:
</p><pre class="screen">
{
"command": "foo",
"arguments": {
"param1": "value1",
"param2": "value2",
...
}
}
</pre><p>
<span class="command"><strong>command</strong></span> is the name of command to execute and
is mandatory. <span class="command"><strong>arguments</strong></span> is a map of parameters
required to carry out the given command. The exact content and
format is command specific.</p><p>The server will process the incoming command and then send a
response of the form:
</p><pre class="screen">
{
"result": 0|1,
"text": "textual description",
"arguments": {
"argument1": "value1",
"argument2": "value2",
...
}
}
</pre><p>
<span class="command"><strong>result</strong></span> indicates the outcome of the command. A value of 0
means success while any non-zero value designates an error. Currently 1 is
used as a generic error, but additional error codes may be added in the
future. <span class="command"><strong>text</strong></span> field typically appears when result is
non-zero and contains a description of the error encountered, but it may
also appear for successful results. That's command specific.
<span class="command"><strong>arguments</strong></span> is a map of additional data values returned by
the server, specific to the command issued. The map is always present, even
if it contains no data values.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ctrl-channel-client"></a>15.2. Using control channel</h2></div></div></div><p>ISC does not provide a client for using control channel. The primary
reason for that is the expectation is that the entity using control channel
is typically an IPAM or similar network management/monitoring software which
may have quite varied expectations regarding the client and is even likely to
be written in languages different than C or C++. Therefore we only provide
examples how one can take advantage of the API.</p><p>The easiest way is to use a tool called <span class="command"><strong>socat</strong></span>,
a tool available from <a class="ulink" href="http://www.dest-unreach.org/socat/" target="_top">socat
homepage</a>, but it is also widely available in Linux and BSD
distributions. Once Kea is started, one could connect to the control
interface using the following command:
</p><pre class="screen">
$ socat UNIX:/path/to/the/kea/socket -
</pre><p>
where <span class="command"><strong>/path/to/the/kea/socket</strong></span> is the path specified in the
<span class="command"><strong>Dhcp4/control-socket/socket-name</strong></span> parameter in the Kea
configuration file.</p><p>It is also easy to open UNIX socket programmatically. An example of
such a simplistic client written in C is available in the Kea Developer's
Guide, chapter Control Channel Overview, section Using Control Channel.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="commands-common"></a>15.3. Commands supported by both DHCPv4 and DHCPv6 servers</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-leases-reclaim"></a>15.3.1. leases-reclaim command</h3></div></div></div><p>
<span class="emphasis"><em>leases-reclaim</em></span> command instructs the server to
reclaim all expired leases immediately. The command has the following
JSON syntax:
</p><pre class="screen">
{
"command": "leases-reclaim",
"arguments": {
"remove": true
}
}
</pre><p>
</p><p>The <span class="emphasis"><em>remove</em></span> boolean parameter is mandatory
and it indicates whether the reclaimed leases should be removed from
the lease database (if true), or they should be left in the
<span class="emphasis"><em>expired-reclaimed</em></span> state (if false). The latter
facilitates lease affinity, i.e. ability to re-assign expired lease to
the same client which used this lease before. See
<a class="xref" href="#lease-affinity" title="9.3. Configuring Lease Affinity">Section 9.3, “Configuring Lease Affinity”</a> for the details. Also, see
<a class="xref" href="#lease-reclamation" title="9.1. Lease Reclamation">Section 9.1, “Lease Reclamation”</a> for the general information
about the processing of expired leases (leases reclamation).</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-list-commands"></a>15.3.2. list-commands command</h3></div></div></div><p>
<span class="emphasis"><em>list-commands</em></span> command retrieves a list of all
commands supported by the server. It does not take any arguments.
An example command may look like this:
</p><pre class="screen">
{
"command": "list-commands",
"arguments": { }
}
</pre><p>
</p><p>
The server will respond with a list of all supported commands. The
arguments element will be a list of strings. Each string will convey
one supported command.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="command-shutdown"></a>15.3.3. shutdown command</h3></div></div></div><p>
<span class="emphasis"><em>shutdown</em></span> command instructs the server to initiate
its shutdown procedure. It is the equivalent of sending a SIGTERM signal
to the process. This command does not take any arguments. An example
command may look like this:
</p><pre class="screen">
{
"command": "shutdown",
"arguments": { }
}
</pre><p>
</p><p>
The server will respond with a confirmation that the shutdown procedure
has been initiated.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="libdhcp"></a>Chapter 16. libdhcp++ library</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#iface-detect">16.1. Interface detection and Socket handling</a></span></dt></dl></div><p>
libdhcp++ is a common library written in C++ that handles
many DHCP-related tasks, including:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">DHCPv4 and DHCPv6 packets parsing, manipulation and assembly</li><li class="listitem">Option parsing, manipulation and assembly</li><li class="listitem">Network interface detection</li><li class="listitem">Socket operations such as creation, data transmission and reception and socket closing.</li></ul></div><p>
</p><p>
While this library is currently used by Kea, it is designed to
be a portable, universal library, useful for any kind of DHCP-related software.
</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="iface-detect"></a>16.1. Interface detection and Socket handling</h2></div></div></div><p>Both the DHCPv4 and DHCPv6 components share network
interface detection routines. Interface detection is
currently supported on Linux, all BSD family (FreeBSD, NetBSD,
OpenBSD), Mac OS X and Solaris 11 systems.</p><p>DHCPv4 requires special raw socket processing to send and receive
packets from hosts that do not have IPv4 address assigned yet. Support
for this operation is implemented on Linux, FreeBSD, NetBSD and OpenBSD.
It is likely that DHCPv4 component will not work in certain cases on
other systems.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="logging"></a>Chapter 17. Logging</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idp54587936">17.1. Logging Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#idp50497936">17.1.1. Loggers</a></span></dt><dt><span class="section"><a href="#idp54763552">17.1.2. Output Options</a></span></dt><dt><span class="section"><a href="#idp54783056">17.1.3. Example Logger Configurations</a></span></dt></dl></dd><dt><span class="section"><a href="#logging-message-format">17.2. Logging Message Format</a></span></dt><dt><span class="section"><a href="#idp52337216">17.3. Logging During Kea Startup</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp54587936"></a>17.1. Logging Configuration</h2></div></div></div><p>
During its operation Kea may produce many messages. They differ in
severity (some are more important than others) and source (some are
produced by specific components, e.g. hooks). It is useful to understand
which log messages are needed and which are not and configure your
logging appropriately. For example, debug level messages can be safely
ignored in a typical deployment. They are, however, very useful when
debugging a problem.
</p><p>
The logging system in Kea is configured through the
<em class="replaceable"><code>Logging</code></em> structure in your configuration
file. All daemons (e.g. DHCPv4 and DHCPv6 servers) will use the
configuration in the <em class="replaceable"><code>Logging</code></em> structure to see
what should be logged and to where. This allows for sharing identical
logging configuration between daemons.
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp50497936"></a>17.1.1. Loggers</h3></div></div></div><p>
Within Kea, a message is logged through an entity called a
"logger". Different components log messages through different
loggers, and each logger can be configured independently of
one another. Some components, in particular the DHCP server
processes, may use multiple loggers to log messages pertaining
to different logical functions of the component. For example,
the DHCPv4 server is using one logger for messages
pertaining to packet reception and transmission, another
logger for messages related to lease allocation and so on.
Some of the libraries used by the Kea servers, e.g. libdhcpsrv
or libhooks library, use their own loggers.
</p><p>
Users implementing hooks libraries (code attached to the server at
runtime) are responsible for creating the loggers used by those
libraries. Such loggers should have unique names, different
from the logger names used by Kea. In this way the
messages emitted from the hooks library can be distingued from
messages issued by the core Kea code. Unique names also allow
the loggers to be configured independently of loggers used
by Kea. Whenever it makes sense, a hook library can use multiple
loggers to log messages pertaining to different logical parts
of the library.
</p><p>
In the <span class="quote">“<span class="quote">Logging</span>”</span> structure of a configuration file
you can specify the configuration for zero or more loggers
(including loggers used by the proprietary hooks libraries). If
there are no loggers specified, the code will use default values which
cause Kea to log messages on at least INFO severity to standard
output.
</p><p>
The three most important elements of a logger configuration
are the <code class="option">name</code> (the component that is
generating the messages), the <code class="option">severity</code>
(what to log), and the <code class="option">output_options</code>
(where to log).
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54842496"></a>17.1.1.1. name (string)</h4></div></div></div><p>
Each logger in the system has a name, the name being that of the
component binary file using it to log messages. For instance, if you
want to configure logging for the DHCPv4 server, you add an entry
for a logger named <span class="quote">“<span class="quote">kea-dhcp4</span>”</span>. This configuration will
then be used by the loggers in the DHCPv4 server, and all the
libraries used by it (unless a library defines its own logger and
there is specific logger configuration that applies to that logger).
</p><p>
When diagnosing the problem with the server's operation, it is often
desired to use the DEBUG logging level to obtain the verbose output
from the server and libraries it uses. However, high verbosity may
be an overkill for the logging system in cases when the server
is processing high volume traffic. To mitigate this problem, Kea
is using multiple loggers, which can be configured independently
and which are responsible for logging messages from different
functional parts of the server. If the user, trying to diagnose the
problem, has a reasonably high confidence that the problem origins
in a specific function of the server, or the problem is related
to the specific type of operation, he may enable high verbosity
only for the relevant logger, thus limiting the debug messages
to the required minimum.
</p><p>
The loggers are associated with a particular library or binary
of Kea. However, each library or binary may (and usually does)
include multiple loggers. For example, the DHCPv4 server binary
contains separate loggers for: packet parsing, for dropped packets,
for callouts etc. Each logger "derives" its configuration from the
root logger. In the typical case, the root logger configuration
is the only logging configuration specified in the configuration
file. Creating a specific configuration for the selected logger,
thus overriding the configuration settings specified in the
root logger configuration, requires putting its configuration
aside of the root logger's configuration with some of the
parameters modified.
</p><p>
To illustrate this, suppose you are using the DHCPv4 server
with the root logger <span class="quote">“<span class="quote">kea-dhcp4</span>”</span> logging at the
INFO level. In order to enable DEBUG verbosity for the DHCPv4
packet drops, you must create configuration entry for the
logger called <span class="quote">“<span class="quote">kea-dhcp4.bad-packets</span>”</span> and specify
severity DEBUG for this logger. All other configuration
parameters may be omited for this logger if the logger should
use the default values specified in the root logger's
configuration.
</p><p>
If there are multiple logger specifications in the configuration
that might match a particular logger, the specification with the
more specific logger name takes precedence. For example, if there
are entries for both <span class="quote">“<span class="quote">kea-dhcp4</span>”</span> and
<span class="quote">“<span class="quote">kea-dhcp4.dhcpsrv</span>”</span>, the DHCPv4 server — and all
libraries it uses that are not dhcpsrv — will log messages
according to the configuration in the first entry
(<span class="quote">“<span class="quote">kea-dhcp4</span>”</span>).
</p><p>
Currently defined loggers are:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>kea-dhcp4</strong></span> - this is the root logger for
the DHCPv4 server. All components used by the DHCPv4 server inherit
the settings from this logger if there is no specialized logger
provided.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.alloc-engine</strong></span> - this is the
logger used by the lease allocation engine, which is responsible
for managing leases in the lease database, i.e. create, modify
and remove DHCPv4 leases as a result of processing messages from
the clients.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.bad-packets</strong></span> - this is the
logger used by the DHCPv4 server daemon for logging inbound client
packets that were dropped or to which the server responded with a
DHCPNAK. The allows administrators to configure a separate log
output that contains only packet drop and reject entries.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.callouts</strong></span> - this logger is used
to log messages pertaining to the callouts registration and execution
for the particular hook point.
</li><li class="listitem"><span class="command"><strong>kea-dhcp4.commands</strong></span> - this logger is used
to log messages relating to the handling of commands received by the
the DHCPv4 server over the command channel.
</li><li class="listitem"><span class="command"><strong>kea-dhcp4.ddns</strong></span> - this logger is used by
the DHCPv4 server to log messages related to the Client FQDN and
Hostname option processing. It also includes log messages
related to the relevant DNS updates.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.dhcp4</strong></span> - this is the logger
by the DHCPv4 server daemon to log basic operations.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.dhcpsrv</strong></span> - this is a base
logger for the libdhcpsrv library.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.eval</strong></span> - this logger is used
to log messages relating to the client classification expression
evaluation code.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.hooks</strong></span> - this logger is used
to log messages related to management of hooks libraries, e.g.
registration and deregistration of the libraries, and to the
initialization of the callouts execution for various hook points
within the DHCPv4 server.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.hosts</strong></span> - this logger is used
within the libdhcpsrv and it logs messages related to the management
of the DHCPv4 host reservations, i.e. retrieval of the reservations
and adding new reservations.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.leases</strong></span> - this logger is used
by the DHCPv4 server to log messages related to the lease allocation.
The messages include detailed information about the allocated or
offered leases, errors during the lease allocation etc.
</li><li class="listitem"><span class="command"><strong>kea-dhcp4.options</strong></span> - this logger is
used by the DHCPv4 server to log messages related to processing
of the options in the DHCPv4 messages, i.e. parsing options,
encoding options into on-wire format and packet classification
using options contained in the received packets.</li><li class="listitem"><span class="command"><strong>kea-dhcp4.packets</strong></span> - this logger
is mostly used to log messages related to transmission of the DHCPv4
packets, i.e. packet reception and sending a response. Such messages
include the information about the source and destination IP addresses
and interfaces used to transmit packets. This logger is also used
to log messages related to subnet selection, as this selection is
usually based on the IP addresses and/or interface names, which can
be retrieved from the received packet, even before the DHCPv4 message
carried in the packet is parsed.
</li><li class="listitem"><span class="command"><strong>kea-dhcp6</strong></span> - this is the root logger for
the DHCPv6 server. All components used by the DHCPv6 server inherit
the settings from this logger if there is no specialized logger
provided.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.alloc-engine</strong></span> - this is the
logger used by the lease allocation engine, which is responsible
for managing leases in the lease database, i.e. create, modify
and remove DHCPv6 leases as a result of processing messages from
the clients.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.bad-packets</strong></span> - this is the
logger used by the DHCPv6 server daemon for logging inbound client
packets that were dropped.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.callouts</strong></span> - this logger is used
to log messages pertaining to the callouts registration and execution
for the particular hook point.
</li><li class="listitem"><span class="command"><strong>kea-dhcp6.commands</strong></span> - this logger is used
to log messages relating to the handling of commands received by the
the DHCPv6 server over the command channel.
</li><li class="listitem"><span class="command"><strong>kea-dhcp6.ddns</strong></span> - this logger is used by
the DHCPv6 server to log messages related to the Client FQDN option
processing. It also includes log messages related to the relevant
DNS updates.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.dhcp6</strong></span> - this is the logger
used DHCPv6 server daemon to log basic operations.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.dhcpsrv</strong></span> - this is a base
logger for the libdhcpsrv library.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.eval</strong></span> - this logger is used
to log messages relating to the client classification expression
evaluation code.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.hooks</strong></span> - this logger is used
to log messages related to management of hooks libraries, e.g.
registration and deregistration of the libraries, and to the
initialization of the callouts execution for various hook points
within the DHCPv6 server.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.hosts</strong></span> - this logger is used
within the libdhcpsrv and it logs messages related to the management
of the DHCPv6 host reservations, i.e. retrieval of the reservations
and adding new reservations.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.leases</strong></span> - this logger is used
by the DHCPv6 server to log messages related to the lease allocation.
The messages include detailed information about the allocated or
offered leases, errors during the lease allocation etc.
</li><li class="listitem"><span class="command"><strong>kea-dhcp6.options</strong></span> - this logger is
used by the DHCPv6 server to log messages related to processing
of the options in the DHCPv6 messages, i.e. parsing options,
encoding options into on-wire format and packet classification
using options contained in the received packets.</li><li class="listitem"><span class="command"><strong>kea-dhcp6.packets</strong></span> - this logger
is mostly used to log messages related to transmission of the DHCPv6
packets, i.e. packet reception and sending a response. Such messages
include the information about the source and destination IP addresses
and interfaces used to transmit packets. This logger is also used
to log messages related to subnet selection, as this selection is
usually based on the IP addresses and/or interface names, which can
be retrieved from the received packet, even before the DHCPv6 message
carried in the packet is parsed.
</li><li class="listitem"><span class="command"><strong>kea-dhcp-ddns</strong></span> - this is the root logger for
the kea-dhcp-ddns daemon. All components used by this daemon inherit
the settings from this logger if there is no specialized logger
provided.</li><li class="listitem"><span class="command"><strong>kea-dhcp-ddns.dhcpddns</strong></span> - this is the logger
used by the kea-dhcp-ddns daemon for logging configuration and global
event information. This logger does not specify logging settings
for libraries used by the daemon.</li><li class="listitem"><span class="command"><strong>kea-dhcp-ddns.dhcp-to-d2</strong></span> - this is the logger
used by the kea-dhcp-ddns daemon for logging information about events
dealing with receiving messages from the DHCP servers and adding them
to the queue for processing.</li><li class="listitem"><span class="command"><strong>kea-dhcp-ddns.d2-to-dns</strong></span> - this is the logger
used by the kea-dhcp-ddns daemon for logging information about events
dealing with sending and receiving messages with the DNS servers.
</li></ul></div><p>
Note that user-defined hook libraries should not use any of those
loggers, and should define new loggers with names that correspond to
the libraries using them. Suppose that the user created the library called
<span class="quote">“<span class="quote">libpacket-capture</span>”</span> to dump packets received and
transmitted by the server to the file. The appropriate name for the
logger could be <span class="command"><strong>kea-dhcp4.packet-capture</strong></span>. Note
that the hook library implementor only specifies the second part
of this name, i.e. <span class="quote">“<span class="quote">packet-capture</span>”</span>. The first part is
a root logger name and is prepended by the Kea logging system.
It is also important to note that since this new logger is a child
of a root logger, it inherits the configuration from the root logger,
unless there is a separate configuration entry for the child logger
which overrides the default configuration.
</p><p>
The list of loggers above excludes any loggers implemented in hooks
libraries. Please consult the documentation of the specific hooks
libraries for the names of loggers they define.
</p><p>Additional loggers may be defined in the future. The easiest
way to find out the logger name is to configure all logging to go
to a single destination and look for specific logger names. See
<a class="xref" href="#logging-message-format" title="17.2. Logging Message Format">Section 17.2, “Logging Message Format”</a> for details.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54751136"></a>17.1.1.2. severity (string)</h4></div></div></div><p>
This specifies the category of messages logged.
Each message is logged with an associated severity which
may be one of the following (in descending order of
severity):
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> FATAL </li><li class="listitem"> ERROR </li><li class="listitem"> WARN </li><li class="listitem"> INFO </li><li class="listitem"> DEBUG </li></ul></div><p>
When the severity of a logger is set to one of these
values, it will only log messages of that severity, and
the severities above it. The severity may also be set to
NONE, in which case all messages from that logger are
inhibited.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54758736"></a>17.1.1.3. output_options (list)</h4></div></div></div><p>
Each logger can have zero or more
<code class="option">output_options</code>. These specify where log
messages are sent. These are explained in detail below.
</p><p>
The other options for a logger are:
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54760992"></a>17.1.1.4. debuglevel (integer)</h4></div></div></div><p>
When a logger's severity is set to DEBUG, this value
specifies what debug messages should be printed. It ranges
from 0 (least verbose) to 99 (most verbose).
</p><p>
If severity for the logger is not DEBUG, this value is ignored.
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54763552"></a>17.1.2. Output Options</h3></div></div></div><p>
The main settings for an output option are the
<code class="option">destination</code> and a value called
<code class="option">output</code>, the meaning of which depends on
the destination that is set.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54765584"></a>17.1.2.1. destination (string)</h4></div></div></div><p>
The destination is the type of output. It can be one of:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> console </li><li class="listitem"> file </li><li class="listitem"> syslog </li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idp54770032"></a>17.1.2.2. output (string)</h4></div></div></div><p>
This value determines the type of output. There are several
special values allowed here: <span class="command"><strong>stdout</strong></span> (messages
are printed on standard output), <span class="command"><strong>stderr</strong></span>
(messages are printed on stderr), <span class="command"><strong>syslog</strong></span> (messages
are logged to syslog using default name, <span class="command"><strong>syslog:name</strong></span>
(messages are logged to syslog using specified name). Any other
value is interpreted as a filename that the logs should be written to.
</p><p>
The other options for <code class="option">output_options</code> are:
</p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="idp54775152"></a>17.1.2.2.1. flush (true of false)</h5></div></div></div><p>
Flush buffers after each log message. Doing this will
reduce performance but will ensure that if the program
terminates abnormally, all messages up to the point of
termination are output. Default is true.
</p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="idp54776752"></a>17.1.2.2.2. maxsize (integer)</h5></div></div></div><p>
Only relevant when destination is file, this is maximum
file size of output files in bytes. When the maximum
size is reached, the file is renamed and a new file opened.
(For example, a ".1" is appended to the name —
if a ".1" file exists, it is renamed ".2",
etc.)
</p><p>
If this is 0, no maximum file size is used.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Due to a limitation of the underlying logging library
(log4cplus), rolling over the log files (from ".1" to
".2", etc) may show odd results: There can be
multiple small files at the timing of roll over. This
can happen when multiple processes try to roll
over the files simultaneously.
Version 1.1.0 of log4cplus solved this problem, so if
this or higher version of log4cplus is used to build
Kea, it shouldn't happen. Even for older versions
it is normally expected to happen rarely unless the log
messages are produced very frequently by multiple
different processes.
</p></div></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="idp54780384"></a>17.1.2.2.3. maxver (integer)</h5></div></div></div><p>
Maximum number of old log files to keep around when
rolling the output file. Only relevant when
<code class="option">output</code> is <span class="quote">“<span class="quote">file</span>”</span>.
</p></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54783056"></a>17.1.3. Example Logger Configurations</h3></div></div></div><p>
In this example we want to set the global logging to
write to the console using standard output.
</p><pre class="screen"><strong class="userinput"><code>
"Logging": {
"loggers": [
{
"name": "kea-dhcp4",
"output_options": [
{
"output": "stdout"
}
],
"severity": "WARN"
}
]
}
</code></strong>
</pre><p>In this second example, we want to store debug log messages
in a file that is at most 2MB and keep up to 8 copies of old logfiles.
Once the logfile grows to 2MB, it will be renamed and a new file
file be created.</p><pre class="screen"><strong class="userinput"><code>
"Logging": {
"loggers": [
{
"name": "kea-dhcp6",
"output_options": [
{
"output": "/var/log/kea-debug.log",
"maxver": 8,
"maxsize": 204800,
"flush": true
}
],
"severity": "DEBUG",
"debuglevel": 99
}
]
}</code></strong></pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="logging-message-format"></a>17.2. Logging Message Format</h2></div></div></div><p>
Each message written to the configured logging
destinations comprises a number of components that identify
the origin of the message and, if the message indicates
a problem, information about the problem that may be
useful in fixing it.
</p><p>
Consider the message below logged to a file:
</p><pre class="screen">2014-04-11 12:58:01.005 INFO [kea-dhcp4.dhcpsrv/27456]
DHCPSRV_MEMFILE_DB opening memory file lease database: type=memfile universe=4</pre><p>
</p><p>
Note: the layout of messages written to the system logging
file (syslog) may be slightly different. This message has
been split across two lines here for display reasons; in the
logging file, it will appear on one line.
</p><p>
The log message comprises a number of components:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">2014-04-11 12:58:01.005</span></dt><dd><p>
The date and time at which the message was generated.
</p></dd><dt><span class="term">INFO</span></dt><dd><p>
The severity of the message.
</p></dd><dt><span class="term">[kea-dhcp4.dhcpsrv/27456]</span></dt><dd><p>
The source of the message. This comprises two elements:
the Kea process generating the message (in this
case, <span class="command"><strong>kea-dhcp4</strong></span>) and the component
within the program from which the message originated
(which is the name of the common library used by DHCP server
implementations). The number after the slash is a process id
(pid).
</p></dd><dt><span class="term">DHCPSRV_MEMFILE_DB</span></dt><dd><p>
The message identification. Every message in Kea
has a unique identification, which can be used as an
index into the <a class="ulink" href="kea-messages.html" target="_top"><em class="citetitle">Kea Messages
Manual</em></a> (<a class="ulink" href="http://kea.isc.org/docs/kea-messages.html" target="_top">http://kea.isc.org/docs/kea-messages.html</a>) from which more information can be obtained.
</p></dd><dt><span class="term">opening memory file lease database: type=memfile universe=4</span></dt><dd><p>
A brief description.
Within this text, information relating to the condition
that caused the message to be logged will be included.
In this example, the information is logged that the in-memory
lease database backend will be used to store DHCP leases.
</p></dd></dl></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp52337216"></a>17.3. Logging During Kea Startup</h2></div></div></div><p>
The logging configuration is specified in the configuration file.
However, when Kea starts, the file is not read until some way into the
initialization process. Prior to that, the logging settings are
set to default values, although it is possible to modify some
aspects of the settings by means of environment variables. Note
that in the absence of any logging configuration in the configuration
file, the settings of (possibly modified) default configuration will
persist while the program is running.
</p><p>
The following environment variables can be used to control the
behavior of logging during startup:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">KEA_LOCKFILE_DIR</span></dt><dd><p>
Specifies a directory where the logging system should create its
lock file. If not specified, it is
<em class="replaceable"><code>prefix</code></em>/var/run/kea, where
<em class="replaceable"><code>prefix</code></em> defaults to /usr/local.
This variable must not end
with a slash. There is one special value: "none", which
instructs Kea to not create lock file at all. This may cause
issues if several processes log to the same file.
</p></dd><dt><span class="term">KEA_LOGGER_DESTINATION</span></dt><dd><p>
Specifies logging output. There are several special values.
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">stdout</span></dt><dd><p>
Log to standard output.
</p></dd><dt><span class="term">stderr</span></dt><dd><p>
Log to standard error.
</p></dd><dt><span class="term">syslog[<span class="optional">:<em class="replaceable"><code>fac</code></em></span>]</span></dt><dd><p>
Log via syslog. The optional
<em class="replaceable"><code>fac</code></em> (which is
separated from the word "syslog" by a colon)
specifies the
facility to be used for the log messages. Unless
specified, messages will be logged using the
facility "local0".
</p></dd></dl></div><p>
Any other value is treated as a name
of the output file. If not specified otherwise, Kea will log to
standard output.
</p></dd></dl></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="faq"></a>Chapter 18. Frequently Asked Questions</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#faq-generic">18.1. Generic Frequently Asked Questions</a></span></dt><dd><dl><dt><span class="section"><a href="#q1-generic">18.1.1. Where did the Kea name came from?</a></span></dt><dt><span class="section"><a href="#q2-generic">18.1.2. Feature X is not supported yet. When/if will it be available?</a></span></dt></dl></dd><dt><span class="section"><a href="#faq-dhcp4">18.2. Frequently Asked Questions about DHCPv4</a></span></dt><dd><dl><dt><span class="section"><a href="#idp51413776">18.2.1. I set up a firewall, but the Kea server still receives the traffic. Why?</a></span></dt></dl></dd><dt><span class="section"><a href="#faq-dhcp6">18.3. Frequently Asked Questions about DHCPv6</a></span></dt><dd><dl><dt><span class="section"><a href="#idp54575072">18.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I checked with tcpdump (or other traffic
capture software) that the incoming traffic is reaching the box. What's wrong?</a></span></dt></dl></dd></dl></div><p>This chapter contains a number of frequently asked questions and
troubleshooting tips. It currently lacks content, but it is expected to grow
over time.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="faq-generic"></a>18.1. Generic Frequently Asked Questions</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="q1-generic"></a>18.1.1. Where did the Kea name came from?</h3></div></div></div><p>Kea is the name of a high mountain parrot living in New Zealand.
See this <a class="ulink" href="https://lists.isc.org/pipermail/kea-users/2014-October/000032.html" target="_top">https://lists.isc.org/pipermail/kea-users/2014-October/000032.html</a>
for an extended answer.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="q2-generic"></a>18.1.2. Feature X is not supported yet. When/if will it be available?</h3></div></div></div><p>Kea is developed by a small team of engineers. Our resources are
limited, so we need to prioritize requests. The complexity of a new
feature (how difficult it is to implement a feature and how likely it
would break something that already works), amount of work required and
expected popularity (i.e., how many users would actually benefit from it)
are three leading factors. We sometimes also have contractual obligations.
</p><p> Simply stating that you'd like feature X is useful. We try to
implement features that are actively requested first, but the reality
is that we have more requests than we can handle, so some of them must
be postponed, at least in the near future. So is your request likely to
be rejected? Not at all. You can do many things to greatly improve the
chances of your request being fulfilled. First, it helps to explain why you
need a feature. If your explanation is reasonable and there are likely
other users that would benefit from it, the chances for Kea developers
to put this task on a roadmap is better. Saying that you are willing
to participate in tests (e.g., test engineering drops when they become
available) is also helpful.</p><p>Another thing you can do to greatly improve the chances of a feature
to appear is to actually develop it on your own and submit a patch.
That's an avenue that people often forget about. Kea is open source
software and we do accept patches. There are certain requirements, like
code quality, comments, unit-tests, documentation, etc., but we have
accepted a significant number of patches in the past, so it's doable.
Accepted contributions range from minor documentation corrections to
significant new features, like support for a new database type. Before
considering writing and submitting a patch, make sure you read
the Contributor's Guide in <a class="ulink" href="http://git.kea.isc.org/~tester/kea/doxygen/" target="_top">Kea Developer's Guide</a>.
</p><p>Kea is developed by ISC, which is a non-profit organization.
You may consider signing a development contract with us. In the past
we did implement certain features due to contractual obligations.
With additional funds we are able to put extra engineering efforts
into Kea development. We can reshuffle our schedule or add extra
hands to the team if needed. Please keep in mind that Kea is
open source software and its principle goal is to provide a good DHCP
solution that can be used by everyone. In other words, we may
refuse a contract that would tie the solution to specific proprietary
technology or make it unusable for other users. Also, we strive to
make Kea a reference implementation, so if your proposal significantly
violates a RFC, we may have a problem with that. Nevertheless, please
talk to us and we may be able to find a solution.</p><p>Finally, Kea has a <a class="ulink" href="http://kea.isc.org/roadmap" target="_top">public
roadmap</a>, with releases happening several times each year. We tend
to not modify plans for the current milestone, unless there are very good
reasons to do so. Therefore "I'd like a feature X in 6 months" is much
better received than "I'd like a feature X now".</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="faq-dhcp4"></a>18.2. Frequently Asked Questions about DHCPv4</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp51413776"></a>18.2.1. I set up a firewall, but the Kea server still receives the traffic. Why?</h3></div></div></div><p>Any DHCPv4 server must be able to receive from and send traffic to
hosts that don't have an IPv4 address assigned yet. That is typically not
possible with regular UDP sockets, therefore the Kea DHCPv4 server uses raw
sockets by default. Raw sockets mean that the incoming packets are received
as raw Ethernet frames, thus bypassing the whole kernel IP stack, including
any firewalling rules your kernel may provide.</p><p>If you do not want the server to use raw sockets, it is possible to
configure the Kea DHCPv4 server to use UDP sockets instead. See <span class="command"><strong>dhcp-socket-type</strong></span>
described in <a class="xref" href="#dhcp4-interface-configuration" title="7.2.4. Interface configuration">Section 7.2.4, “Interface configuration”</a>. However,
using UDP sockets has certain limitations. In particular, they may not allow
for sending responses directly to clients without IPv4 addresses assigned.
That's ok, if all your traffic is coming through relay agents.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="faq-dhcp6"></a>18.3. Frequently Asked Questions about DHCPv6</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp54575072"></a>18.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I checked with tcpdump (or other traffic
capture software) that the incoming traffic is reaching the box. What's wrong?</h3></div></div></div><p>Please check whether your OS has any IPv6 filtering rules. Many
operating systems are shipped with firewalls that discard incoming IPv6
traffic by default. In particular, many Linux distributions do that. Please
check the output of the following command:
</p><pre class="screen">
# <strong class="userinput"><code>ip6tables -L -n</code></strong></pre><p>
One common mistake in this area is to use <span class="command"><strong>iptables</strong></span> tool,
which lists IPv4 firewall rules only.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="acknowledgments"></a>Chapter 19. Acknowledgments</h1></div></div></div><p>Kea is primarily designed, developed, and maintained by
Internet Systems Consortium, Inc. It is an open source project
and contributions are welcomed.</p><p>Support for the development of the DHCPv4, DHCPv6 and
DHCP-DDNS components was provided by
<a class="ulink" href="http://www.comcast.com/" target="_top">Comcast</a>.</p><p>Kea was initially implemented as a collection of applications
within the BIND 10 framework. Hence, Kea development would not be
possible without the generous support of past BIND 10 project sponsors.</p><p><a class="ulink" href="http://jprs.co.jp/" target="_top">JPRS</a> and
<a class="ulink" href="http://cira.ca/" target="_top">CIRA</a> were Patron Level
BIND 10 sponsors.</p><p><a class="ulink" href="https://www.afnic.fr/" target="_top">AFNIC</a>,
<a class="ulink" href="https://www.cnnic.net.cn/" target="_top">CNNIC</a>,
<a class="ulink" href="https://www.nic.cz/" target="_top">CZ.NIC</a>,
<a class="ulink" href="http://www.denic.de/" target="_top">DENIC eG</a>,
<a class="ulink" href="https://www.google.com/" target="_top">Google</a>,
<a class="ulink" href="https://www.ripe.net/" target="_top">RIPE NCC</a>,
<a class="ulink" href="https://registro.br/" target="_top">Registro.br</a>,
<a class="ulink" href="https://nzrs.net.nz/" target="_top">.nz Registry Services</a>, and
<a class="ulink" href="https://www.tcinet.ru/" target="_top">Technical Center of Internet</a>
were past BIND 10 sponsors.</p><p><a class="ulink" href="https://www.afilias.info/" target="_top">Afilias</a>,
<a class="ulink" href="https://www.iis.se/" target="_top">IIS.SE</a>,
<a class="ulink" href="http://www.nominet.org.uk/" target="_top">Nominet</a>, and
<a class="ulink" href="https://www.sidn.nl/" target="_top">SIDN</a> were founding
sponsors of the BIND 10 project.</p></div></div></body></html>
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