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<h1><center>HTB FAQ</center></h1>
<center><address>
Martin Devera aka devik (devik@cdi.cz)<br>
Last updated: 7.7.2003
</address></center>
<br>
<b>How to set single HTB up for more interfaces or for incoming packets</b>
<p>
You need IMQ for this because all qdisc can handle only outgoing
traffic on single interface. See
<a href="http://www.linuximq.net/">http://www.linuximq.net/</a>.
<p>
<b>When HTB is used on machine with Apache (FTP, Samba, ...) server running
then downloading from it can't be limited precisely</b>
<p>
Try to add PFIFO with limit 10 under HTB classes. When you use default
(much larger PFIFO) or SFQ then TCP stack will back off itself as it
see too large memory used for outgoing packets. You can also play
with /proc/sys/net/ipv4/tcp_wmem.
<p>
<b>"HTB: mindelay=500, report it please !" messages in syslog</b>
<p>
This means that all indicated that some class should be ready
soon but when we looked for it we haven't found one which will
be ready in 5 seconds.
<br>
After this message you can see lines like
<pre>
kernel: htb*g j=154480191
kernel: htb*r7 m=0
kernel: htb*r6 m=0
kernel: htb*r5 m=0
kernel: htb*r4 m=0
kernel: htb*r3 m=0
kernel: htb*r2 m=0
kernel: htb*r1 m=0
kernel: htb*r0 m=0
kernel: htb*c20110 m=2 t=636487 c=17888 pq=0 df=483328 ql=0 pa=0 f:
kernel: htb*c20220 m=1 t=-59999999 c=42404 pq=154487461 df=450560 ql=14 pa=40 f:
kernel: htb*c20001 m=2 t=5131 c=6439 pq=0 df=8192 ql=0 pa=0 f:
</pre>
If you decide to treat is as real bug then I'll need all of these. They
are logged under kernel.debug facility so often you need to add it so
your syslog.conf. These "htb*" are dump of internal state of all classes.
c20110 means class 2:110. *r lines are states of row activity bitsmasks.
*c indicates stet of all classes. You are interested in classes
with m=1 resp. m=0. These will become ready after time -c resp. -t whatever
is negative and smaller.
It is 59999999 us for class 2:110 above which is 59sec. It is way too much
and HTB will spill that error because it is > 5 sec.
<p>
<i>So what is the problem ?</i> Probably you have too small rate or ceil
for such class - you should use at least 4kbit for realiable operation
of HTB - it leads to max 3sec of delay for 1500 byte packets which seems
as reasonable value.
<br>
Also try <a href=v3/htb_3.7_delay_bug.patch>this</a> patch against 2.4.20.
(works against older too with one reject). It increases timeout to
10secs and makes errors more readable.
<i>I'm interested in your experiences (good or bad) with the patch !</i>
<br>
If you think it is not the case and you still get weird errors, contact
me with syslog data above and output of commands
<pre>
tc -s -d qdisc
tc -s -d class show dev your_htb_device1_here
tc -s -d class show dev your_htb_device2_here
...
</pre>
<p>
<b>Why HTB sharing setup works with eth0 but on lo (loopback)
it exhibits weird rates ?
</b>
<p>Try to execute
<pre>
ifconfig lo mtu 1500
</pre>
or use parameter mtu 16400 on "tc qdisc add" line. It is because
HTB reserves rate table for 1500 bytes long packets and loopback
uses 16384 as default.
<p>
<b>What's difference between kbps and kbit ?
</b>
<p>
1kbps=8kbit. Don't forget it !
<p>
<b>What if sum of child rates is smaller than parent rate ?
</b>
<p>
It is like if you create unused child with remaining rate - the
rate difference is divided between other children.
<p>
<b>What if sum of child rates is greater than parent rate ?
</b>
<p>
Then interesting things can happen. Total rate delivered
by children can be higher that parent's rate (thus its rate
is not respected). However when sum of actual child rates are
under parent's rate then borrowing will occur like in regular case.
<p>
I use setup with 4 classes, parent has rate=ceil=6kbps, child
"mail" has rate=1kbps ceil=4kbps, "web" has rate=ceil=15kbps
and "other" has rate=2kbps ceil=4kbps.
HTB is attached to an PPP interface with compressed multilink pair
of modems which can go from 6kbps to cca 16kbps (depends on compresability
of data). When "web" traffic is present it can go as high as compression
allows while still allowing mail 1kbps and other 2kbps.
<br>
When "web" traffic is smaller than 6kbps then "mail" and "other"
can borrow more bw up to 4k each.
Parent's class it not set to 18k because then "mail" and "other"
could get as much as 8k which is more that link's minimum and
would saturate the link. Thus I set parent to 6k so that
"mail"+"other" are limited to 6k while "web" can go over.
<p>
You can do similar setup by using one more class and deeper hierarchy
but this is just to show you the possibility.
<p>
<b>"RTNETLINK answers: Invalid argument" and tc parameters are correct
</b>
<p>
Probably you use tc tool not suited for HTB in kernel. Reread
main HTB page section Downloads.
<p>
<b>All packets are dropped when "default" is set to nonleaf
</b>
<p>
Yes. Default kwyword must point to leaf or be 0 (so unclassified
packets go thru directly). If you want to "direct" other packets
to non-leaf do it by catch all filter with the largest "pref".
<p>
<b>What tool was used to create graphs in HTB manual ?
</b>
<p>
It is proprietary tool called ethloop
(<a href=http://luxik.cdi.cz/~devik/qos/ethloop/>luxik.cdi.cz/~devik/qos/ethloop/</a>).
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