Multicast Being Forwarded from one Mrouter to Another - for no reason ?

[Shlomy Maron]

I have an environment of L3 N5K switch connected to 4500x (L2 Switch).

they have PIM and eigrp neighbor relationship over the same interface VLAN.

I've added a new N5K L3 Switch (N5K2) - I've added it to the same VLAN for the EIGRP and PIM neighbor relationship.

at the moment there is nothing connected to N5K2 - all the hosts are connected to N5K1.

there are multicast streams from the Core Switch that are going towards hosts at N5K1.

for some reason - the same multicast are arriving N5K2 - despite the fact it has no hosts that are listenning to it.

looking at http://lisa.mindbit.ro/wiki/doku.php?id=igmp_snooping 

the IGMP beavhior should be that multicast from 1 Mrouter interfece will not go to another mrouter interface unless the mrouter had joined that group.

so why am I getting these multicasts ?

[Vasilii Mikhailovskii · Accepted solution]

Hello.

I'm not sure about the article.

Per RFC 4541 (section 2.1.2):

1) Packets with a destination IP address outside 224.0.0.X which are
      not IGMP should be forwarded according to group-based port
      membership tables and must also be forwarded on router ports.

You may also find interesting the questionnaire in section 4 of RFC (and question 6).

[Shlomy Maron]

Hi Vasilii,

thanks for your help ! I think you are correct.

I think that the solution would be to activate pim snooping.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/snooppim.html

but how do I activate pim snooping on 4500X ? the command IP pim snooping doesn't work.