Re: Rate Limiting on Cisco Router

[gordon b slater <gordslater () ieee org>]

On Thu, 2010-07-08 at 16:35 -0700, Kenny Sallee wrote:
> I think if you try to traffic-shape 80Mbps on that platform you'll have
> problems.  We have a 7200 with NPE-G1 (rate limited at 80Mbps) and it killed
> the CPU when the threshold was hit.  I imagine that traffic-shaping would do
> the same to CPU and memory.  I'd lab it first.

I've seen that model preceded by a BSD machine with 2 physical ethernet
NICs. When I asked - "limiting for the 7206's outgoing", so I'm assuming
that was a CPU thing. In that case the 7206 was just an edge box for the
fibre, so doing nothing complex. Capped at 48Mbps (IIRC) in that case -
YMMV. 

Also bear in mind that this is borderline black art - it needs a bit of
testing to be sure it's working as you expect :)

My usual technique is to replay some flows then set several iperf
streams going simultaneously to see how it reacts. Sometimes limiting
just seems to temporarily break down under stress in bizarre ways.
Whether it fails "open", "restricted" or "closed" seems to be very
unpredictable and not very reproducible on some kit- keep your eye on it
at first, or use BSD to do it if you're more familiar with that.


Gord
--
Awake! for morning in the bowl of light has flung the stone that puts
the stars to flight