[c-nsp] Cat4500 High CPU with Multicast Stream

[Antonio Soares]

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