/usr/src/xtables-addons-2.6/extensions/libxt_IPMARK.man is in xtables-addons-dkms 2.6-1.
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Allows you to mark a received packet basing on its IP address. This
can replace many mangle/mark entries with only one, if you use
firewall based classifier.
.PP
This target is to be used inside the \fBmangle\fP table.
.TP
\fB\-\-addr\fP {\fBsrc\fP|\fBdst\fP}
Select source or destination IP address as a basis for the mark.
.TP
\fB\-\-and\-mask\fP \fImask\fP
Perform bitwise AND on the IP address and this bitmask.
.TP
\fB\-\-or\-mask\fP \fImask\fP
Perform bitwise OR on the IP address and this bitmask.
.TP
\fB\-\-shift\fP \fIvalue\fP
Shift addresses to the right by the given number of bits before taking it
as a mark. (This is done before ANDing or ORing it.) This option is needed
to select part of an IPv6 address, because marks are only 32 bits in size.
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The order of IP address bytes is reversed to meet "human order of bytes":
192.168.0.1 is 0xc0a80001. At first the "AND" operation is performed, then
"OR".
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Examples:
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We create a queue for each user, the queue number is adequate
to the IP address of the user, e.g.: all packets going to/from 192.168.5.2
are directed to 1:0502 queue, 192.168.5.12 -> 1:050c etc.
.PP
We have one classifier rule:
.IP
tc filter add dev eth3 parent 1:0 protocol ip fw
.PP
Earlier we had many rules just like below:
.IP
iptables \-t mangle \-A POSTROUTING \-o eth3 \-d 192.168.5.2 \-j MARK
\-\-set\-mark 0x10502
.IP
iptables \-t mangle \-A POSTROUTING \-o eth3 \-d 192.168.5.3 \-j MARK
\-\-set\-mark 0x10503
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Using IPMARK target we can replace all the mangle/mark rules with only one:
.IP
iptables \-t mangle \-A POSTROUTING \-o eth3 \-j IPMARK \-\-addr dst
\-\-and\-mask 0xffff \-\-or\-mask 0x10000
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On the routers with hundreds of users there should be significant load
decrease (e.g. twice).
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(IPv6 example) If the source address is of the form
2001:db8:45:1d:20d:93ff:fe9b:e443 and the resulting mark should be 0x93ff,
then a right-shift of 16 is needed first:
.IP
\-t mangle \-A PREROUTING \-s 2001:db8::/32 \-j IPMARK \-\-addr src \-\-shift
16 \-\-and\-mask 0xFFFF
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