[Hidden-tech] Cisco Router rate limiting

[R. David Murray]

On Tue, 26 Oct 2010 15:54:58 -0400, David Korpiewski <davidk at cs.umass.edu> wrote:
> I'd be interested in knowing how to do resource reservation for 
> preferred traffic instead.  Any advice would be very appreciated :-)

Heh.  I think I shouldn't have used the term 'resource reservation'.
I was using it in a colloquial sense, forgetting that RSVP uses
it with a particular technical meaning.

Anyway, what I'm referring to is really priority queueing, and goes
something like this:


    class-map match-any TS
      match access-group 120
     
    policy-map llq
      class TS
       priority 1024
      class class-default
       fair-queue

    interface Serial0
      service-policy output llq

    access-list 120 permit tcp 192.168.200.0 0.0.7.255 192.168.200.0 0.0.7.255 eq 3389


This will give priority to outbound traffic whose source or destination
port is 3398 on S1, up to 1024K bits per second (2/3 of the T1), but if
there isn't that much port 3398 traffic, any leftover bandwidth will be
available to the remainder of the traffic using the default prioritization
(that's the fair queue default).

You can set this on your ethernet port too, but that won't have much
effect since you generally don't get a queue buildup on the ethernet
port when the traffic is bottlenecked at the T1.

It also does no good to set it on the input traffic, since draining
the queue once the packets are sitting on the router isn't the problem.
What the llq config is doing is making sure the terminal services packets
get priority when they are sent over the bottleneck (highest latency)
link, and consequently delaying the packets that don't have priority.
It doesn't *quite* make it as if the other traffic doesn't exist, but
it's about as close as you can get to that ideal.

To make this work well you really need to have control of both sides
of the slow link and do the outbound llq on both sides.  It sounds like
you have that.

--
R. David Murray                                      www.bitdance.com