Re: [LARTC] FW: Traffic shaping in conjunction with QoS

[bert hubert <ahu@ds9a.nl>]

On Thu, Dec 06, 2001 at 02:58:40PM -0600, Phil Doroff wrote:

> The jist of my problem is this.  I need to ratelimit an entire interface
> (all traffic) to 1.5mbit/sec.  Now, this is obviously really easy and
> accurate to do with a tbf qdisc, but when the 1.5mbit gets nailed, things
> like ssh tend to suffer a bit with added latency.  Not to mention the game
> servers that are run on the box (but that's not the issue right now, lets
> stick with SSH. ;)

If you set your limit/latency low enough, latency will be reasonable, but
you can do cooler things:

> Now, what I want to do is limit the interface to 1.5mbit but ALSO allow
> interactive (relying for now on the application to set the correct bits)
> precedence over all other traffic.  I.e. ssh traffic.  Obviously a prio rule
> here works very well for prioritizing the traffic (or in this case a pfifo
> would work just as well), but I can't limit *all* traffic to 1.5mbit.  I can
> limit each category of traffic to whatever I want, but I can't have them
> combined.  (i.e. I could "give" ssh 500kbit/sec but I can't say "if ssh
> isn't using all that bandwidth, give it up to the other greedy services").

You could make PRIO qdisc, make a filter that sends up to 25kbits/second of
SSH traffic to band 0, and everything else to band 1. Band 1 would then
contain a TBF set to 1.5mbit/s-25kbit/s.

See
http://ds9a.nl/lartc/HOWTO/cvs/2.4routing/output/2.4routing-12.html#ss12.3
for how to make policing filters. 

> I looked over cbq a bit, but it seems way too complex, and definitely too
> inaccurate to use if I can help it.  But if needed, I'm game.  I also
> attempted to get HTB working via the kernel patches, but it seems it doesn't
> work quite right (if I try to follow the step-by-step examples things start
> to error halfway trhough.. it even killed the box once when I hit it with a
> lot of data). The reason I want to use the QoS bits is because people scp

Devik will be very interested in hearing the details! One crasher bug has
been fixed recently. Please inform him of your problems!

> large files off this box quite often, and that's the only way to distinguish
> scp from ssh traffic.

True. You can even match on those with filters, I just added TOS selection
to
  http://ds9a.nl/lartc/HOWTO/cvs/2.4routing/output/2.4routing-9.html#ss9.5

> What would be ideal, is a TBF filter on the interface, with a prio filter
> behind that.  (prio as opposed to pfifo so I can later add rulesets for
> certain TCP ports to give them priority over "everything else").  Obviously

You just described HTB :-)

> I guess where I'm getting confused is the whole stateful/unstateful qdisc
> thing.

Classful/unclassful.

> thanks much!  I hope to be around a while here, there is some seriously
> interesting stuff.  Makes for some good reading.

Just bug Devik about the problems you see with HTB. The more you can help
him, the earlier HTB will be *rock-solid* and in the mainline kernel.

Regards,

bert

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