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