[c-nsp] Filtering Layer 2 Multicasts on 6509

[Sebastian Wiesinger]

* Pete Lumbis <alumbis at gmail.com> [2011-01-20 22:26]:
> Devin,
> 
> I did a bunch of testing and checking in the lab and here is the scoop:
> Any multicast mac that is received on an SVI will be punted. The short
> reason is because we only look for the "01" in the MAC to indicate
> that this is multicast then we flood to the VLAN. Unlike a unicast

Hi Pete,

I had something like this occur on a Catalyst 4500. It seems that all
"Link-local" Multicast (224.0.0.0/24) is ALWAYS punted even without an
SVI (only L2). There is no way to say "This is only a switch, just
flood it and don't send it to the CPU."

CoPP doesn't really help because then the packet is dropped and not
forwarded at all which is a bad thing(tm) for stuff like OSPF, HSRP,
VRRP, etc.

I don't know if the platform could support a feature to keep multicast
from being punted to the CPU but if so I could really use it.

Regards,

Sebastian

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