[c-nsp] Filtering Layer 2 Multicasts on 6509

[Tóth András]

Hi Sebastian,

There is a solution for your problem for 4500 switches which is called
per-vlan capture mode. You can enable it with the 'access-list
hardware capture mode vlan' command. This will make sure special
multicast traffic is punted to CPU only in case there's an SVI for
that vlan.

Refer to the "Selecting Mode of Capturing Control Packets" section on
the following link:
http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/54sg/configuration/guide/secure.html#wp1128851


Best regards,
Andras


On Fri, Jan 21, 2011 at 12:09 AM, Sebastian Wiesinger
<cisco-nsp at ml.karotte.org> wrote:
> * 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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