[c-nsp] Cat4500 High CPU with Multicast Stream

[Chris Evans]

Check the ttl on the multicast stream. A ttl of 1 will cause it to hit the
CPU of your first hop router.
On Jul 13, 2011 8:02 AM, "Antonio Soares" <amsoares at netcabo.pt> wrote:
> Hello group,
>
> I have a customer with a few 3560/3750's and one 4500/SUP5 acting as the
> core switch.
>
> For some reason, when a user start one multicast stream, the 4500 suffers
> high cpu utilization and the network is affected. Only the 4500 suffers of
> this problem, the 3560/3750's don't have any complaints.
>
> I see that the 4500 is a CEF based platform and I know that IP Multicast
is
> not supported in the CEF path. So I was expecting to have this traffic
> switched in hardware or fast-switched. But a packet capture shows me that
> the traffic goes to the cpu. I used this debug and output to confirm this:
>
> debug platform packet all receive buffer
>
> show platform cpu packet buffered
>
> The processes that eat most of the cpu are "Cat4k Mgmt LoPri" and "Cat4k
> Mgmt HiPri". We thought this could be a bug and we upgraded the 4500 to
the
> latest release but the problem is exactly the same. The multicast stream
is
> processed by the cpu.
>
> Anyone has seen this before ? Is this normal behavior of the 4500 ?
>
> Usually the multicast streams are destined to 224.x.x.x. The end users do
> not respect the 239 rule.
>
>
> Thanks.
>
> Regards,
>
> Antonio Soares, CCIE #18473 (R&S/SP)
> amsoares at netcabo.pt
> http://www.ccie18473.net
>
>
>
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