HTB FAQ

#
HTB FAQ

How to set single HTB up for more interfaces or for incoming packets

You need IMQ for this because all qdisc can handle only outgoing traffic on single interface. See http://www.linuximq.net/.

When HTB is used on machine with Apache (FTP, Samba, ...) server running then downloading from it can't be limited precisely

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.

"HTB: mindelay=500, report it please !" messages in syslog

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.
After this message you can see lines like

    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:

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.

So what is the problem ? 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.
Also try this patch against 2.4.20. (works against older too with one reject). It increases timeout to 10secs and makes errors more readable. I'm interested in your experiences (good or bad) with the patch !
If you think it is not the case and you still get weird errors, contact me with syslog data above and output of commands

    tc -s -d qdisc
    tc -s -d class show dev your_htb_device1_here
    tc -s -d class show dev your_htb_device2_here
    ...

Why HTB sharing setup works with eth0 but on lo (loopback) it exhibits weird rates ?

Try to execute

    ifconfig lo mtu 1500

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.

What's difference between kbps and kbit ?

1kbps=8kbit. Don't forget it !

What if sum of child rates is smaller than parent rate ?

It is like if you create unused child with remaining rate - the rate difference is divided between other children.

What if sum of child rates is greater than parent rate ?

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.

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.
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.

You can do similar setup by using one more class and deeper hierarchy but this is just to show you the possibility.

"RTNETLINK answers: Invalid argument" and tc parameters are correct

Probably you use tc tool not suited for HTB in kernel. Reread main HTB page section Downloads.

All packets are dropped when "default" is set to nonleaf

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".

What tool was used to create graphs in HTB manual ?

It is proprietary tool called ethloop (luxik.cdi.cz/~devik/qos/ethloop/).