[c-nsp] what would be the normal burst size in policer on 3550 cisco switch for 500Mbps

[Saku Ytti]

On (2014-11-05 21:32 +0100), Per Carlson wrote:

> > what would be the normal burst size in policer on 3550 cisco switch for 500
> > Mbps.
> 
> A common rule of thumb for best effort (TCP) traffic is a burst size of 1.5
> seconds. The math is left for your  exercise.

I often see people offering some kind of formulas for this, sometimes using
RTT, sometimes using policer rate.
We should care about ingress rate, when configuring egress policer burst size.
Because ingress is dictating how fast the bucket can fill, policer rate
dictating how fast it can empty.

To determine useful burst size, you must know where the traffic is coming in
from, as that is setting your worst case.
1.5s is very long time, these boxes often have single digit millisecond
buffering to begin with.
I would start with much more modest number, maybe 5ms * ingress_rate, that
would already be 610kB for accepting 5ms burst from 1GE ingress.


-- 
  ++ytti