That's not really the critical thing, so much as - you need an IGMP querier active in the VLAN in order for snooping to work correctly/reliably. Some applications may behave fine without; others won't. The key is periodic joins from the hosts are required to maintain membership state for snooping. The querier ensures that happens.

So what you really need is an SVI *with* an IP address for that vlan, and then enable igmp snooping querier for that vlan. The configured IP is used to source queries. The SVI in this case can actually be shutdown, it doesn't really matter.

The config is like:
int vlan 200
 ip add 10.1.1.1/24
 ip igmp snooping querier
 shut

The other option is to just enable PIM on the (admin up) SVI in the vlan, but you may not want to do that, depends on the network design.

int vlan 200
 ip add 10.1.1.1/24
 ip pim sparse
 no shut

HTH,
Tim



At 10:46 AM 7/12/2009, Adrian Minta remarked:

Phil Mayers wrote:
>
> Config? Software version?
>
> If you don't already have it, try creating an un-numbered SVI e.g.:
>
> vlan 200
>  name multicast
> int Vlan200
>  no ip address
>
> I seem to recall references to this being required for some multicast
> functionality on some versions of 6500/7600 IOS
>
>
Seems weird, but I will give it a try !

--
Best regards,
Adrian Minta


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Tim Stevenson, [email protected]
Routing & Switching CCIE #5561
Technical Marketing Engineer, Cisco Nexus 7000
Cisco - http://www.cisco.com
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