[c-nsp] 7600 ES line card traffic policing outbound

[Saku Ytti]

On 31 August 2016 at 16:51, James Bensley <jwbensley at gmail.com> wrote:

Hey,

> Even if it does have a correct (large enough) burst size set, when you
> trying to police in the range of Gbps on these cards, you might be
> hitting the max burst limit. For LAN cards its around 31250000 bytes
> (circa 250Mbits per second).

Consider 3Gbps * 300ms = 112.5MB, so your TCP window needs to grow to
112.5MB to get 3Gbps rate on 300ms latency. TCP windows grow
exponentially, so worst case window growth could be ~56MB, sender
could be 100Gbps for all we know, so we could be looking at this 56MB
bursting all at once. If you can't send it through policer, window
fails to grow, and full 3Gbps can't be done on single TCP session.

On the flip side if you do allow 56MB bursts at linerate, that'll not
give you very good QoS, and you might end up congesting some buffers
along the way, so it's going to be compromise any way you look at it.

I would recommend OP configures shaping instead.
-- 
  ++ytti