[c-nsp] CEF and multicast on a 3750

[John Neiberger]

On Tue, Jun 26, 2012 at 2:48 PM, Saku Ytti <saku at ytti.fi> wrote:
> On (2012-06-26 22:07 +0200), Gert Doering wrote:
>
>> Haaaahahaa... so the 3750 has the same issues the 2960 has - if you
>> turn on "mls qos", the tiny buffers get reduced to tiny/4 buffers,
>
> Common misconception. Just turning 'mls qos' on makes situation worse for
> microbursts, but tuning it correctly it behaves better than no 'mls qos'.
> Unfortunately good documentations are not searchable via CCO.
>
> https://supportforums.cisco.com/docs/DOC-8093#_Toc191205672
> --
>  ++ytti

In our case, around 99.99% of the traffic on that switch is multicast
video that is all marked the same way. In that sort of situation, QoS
isn't going to help and it adds additional latency because the
scheduler still has to check all the queues. (At least that's what the
SME from Cisco said.) Turning off mls qos re-enables FIFO and
decreases latency by getting rid of the unnecessary scheduler.

John