debian/doc/htb/htbfaq.htm

   1 <html><head><title>HTB FAQ</title></head>
   2 <body>
   3 <h1><center>HTB FAQ</center></h1>
   4 <center><address>
   5 Martin Devera aka devik (devik@cdi.cz)<br>
   6 Last updated: 7.7.2003
   7 </address></center>
   8 <br>
   9 <b>How to set single HTB up for more interfaces or for incoming packets</b>
  10 <p>
  11 You need IMQ for this because all qdisc can handle only outgoing
  12 traffic on single interface. See
  13 <a href="http://www.linuximq.net/">http://www.linuximq.net/</a>.
  14 <p>
  15 <b>When HTB is used on machine with Apache (FTP, Samba, ...) server running
  16    then downloading from it can't be limited precisely</b>
  17 <p>
  18 Try to add PFIFO with limit 10 under HTB classes. When you use default
  19 (much larger PFIFO) or SFQ then TCP stack will back off itself as it
  20 see too large memory used for outgoing packets. You can also play
  21 with /proc/sys/net/ipv4/tcp_wmem.
  22 <p>
  23 <b>"HTB: mindelay=500, report it please !" messages in syslog</b>
  24 <p>
  25 This means that all indicated that some class should be ready
  26 soon but when we looked for it we haven't found one which will
  27 be ready in 5 seconds.
  28 <br>
  29 After this message you can see lines like
  30 <pre>
  31 kernel: htb*g j=154480191
  32 kernel: htb*r7 m=0
  33 kernel: htb*r6 m=0
  34 kernel: htb*r5 m=0
  35 kernel: htb*r4 m=0
  36 kernel: htb*r3 m=0
  37 kernel: htb*r2 m=0
  38 kernel: htb*r1 m=0
  39 kernel: htb*r0 m=0
  40 kernel: htb*c20110 m=2 t=636487 c=17888 pq=0 df=483328 ql=0 pa=0 f:
  41 kernel: htb*c20220 m=1 t=-59999999 c=42404 pq=154487461 df=450560 ql=14 pa=40 f:
  42 kernel: htb*c20001 m=2 t=5131 c=6439 pq=0 df=8192 ql=0 pa=0 f:
  43 </pre>
  44 If you decide to treat is as real bug then I'll need all of these. They
  45 are logged under kernel.debug facility so often you need to add it so
  46 your syslog.conf. These "htb*" are dump of internal state of all classes.
  47 c20110 means class 2:110. *r lines are states of row activity bitsmasks.
  48 *c indicates stet of all classes. You are interested in classes
  49 with m=1 resp. m=0. These will become ready after time -c resp. -t whatever
  50 is negative and smaller.
  51 It is 59999999 us for class 2:110 above which is 59sec. It is way too much
  52 and HTB will spill that error because it is &gt; 5 sec.
  53 <p>
  54 <i>So what is the problem ?</i> Probably you have too small rate or ceil
  55 for such class - you should use at least 4kbit for realiable operation
  56 of HTB - it leads to max 3sec of delay for 1500 byte packets which seems
  57 as reasonable value.
  58 <br>
  59 Also try <a href=v3/htb_3.7_delay_bug.patch>this</a> patch against 2.4.20.
  60 (works against older too with one reject). It increases timeout to
  61 10secs and makes errors more readable.
  62 <i>I'm interested in your experiences (good or bad) with the patch !</i>
  63 <br>
  64 If you think it is not the case and you still get weird errors, contact
  65 me with syslog data above and output of commands
  66 <pre>
  67 tc -s -d qdisc
  68 tc -s -d class show dev your_htb_device1_here
  69 tc -s -d class show dev your_htb_device2_here
  70 ...
  71 </pre>
  72
  73 <p>
  74 <b>Why HTB sharing setup works with eth0 but on lo (loopback)
  75         it exhibits weird rates ?
  76 </b>
  77 <p>Try to execute
  78 <pre>
  79 ifconfig lo mtu 1500
  80 </pre>
  81 or use parameter mtu 16400 on "tc qdisc add" line. It is because
  82 HTB reserves rate table for 1500 bytes long packets and loopback
  83 uses 16384 as default.
  84 <p>
  85 <b>What's difference between kbps and kbit ?
  86 </b>
  87 <p>
  88 1kbps=8kbit. Don't forget it !
  89 <p>
  90 <b>What if sum of child rates is smaller than parent rate ?
  91 </b>
  92 <p>
  93 It is like if you create unused child with remaining rate - the
  94 rate difference is divided between other children.
  95 <p>
  96 <b>What if sum of child rates is greater than parent rate ?
  97 </b>
  98 <p>
  99 Then interesting things can happen. Total rate delivered
 100 by children can be higher that parent's rate (thus its rate
 101 is not respected). However when sum of actual child rates are
 102 under parent's rate then borrowing will occur like in regular case.
 103 <p>
 104 I use setup with 4 classes, parent has rate=ceil=6kbps, child
 105 "mail" has rate=1kbps ceil=4kbps, "web" has rate=ceil=15kbps
 106 and "other" has rate=2kbps ceil=4kbps.
 107 HTB is attached to an PPP interface with compressed multilink pair
 108 of modems which can go from 6kbps to cca 16kbps (depends on compresability
 109 of data). When "web" traffic is present it can go as high as compression
 110 allows while still allowing mail 1kbps and other 2kbps.
 111 <br>
 112 When "web" traffic is smaller than 6kbps then "mail" and "other"
 113 can borrow more bw up to 4k each.
 114 Parent's class it not set to 18k because then "mail" and "other"
 115 could get as much as 8k which is more that link's minimum and
 116 would saturate the link. Thus I set parent to 6k so that
 117 "mail"+"other" are limited to 6k while "web" can go over.
 118 <p>
 119 You can do similar setup by using one more class and deeper hierarchy
 120 but this is just to show you the possibility.
 121 <p>
 122 <b>"RTNETLINK answers: Invalid argument" and tc parameters are correct
 123 </b>
 124 <p>
 125 Probably you use tc tool not suited for HTB in kernel. Reread
 126 main HTB page section Downloads.
 127 <p>
 128 <b>All packets are dropped when "default" is set to nonleaf
 129 </b>
 130 <p>
 131 Yes. Default kwyword must point to leaf or be 0 (so unclassified
 132 packets go thru directly). If you want to "direct" other packets
 133 to non-leaf do it by catch all filter with the largest "pref".
 134 <p>
 135 <b>What tool was used to create graphs in HTB manual ?
 136 </b>
 137 <p>
 138 It is proprietary tool called ethloop
 139 (<a href=http://luxik.cdi.cz/~devik/qos/ethloop/>luxik.cdi.cz/~devik/qos/ethloop/</a>).
 140
 141 </body></html>