Solved: 2950 and igmp snooping

Ronyn____ · ‎09-30-2009

Hi

I have got stand alone 2950 switch and a few multicast sources and receivers connected to it. I enabled IGMP Snooping, but it seems that the multicast traffic is flooded to all ports. The configuration is as follows:

IGMP Snooping enabled

IGMP filtering disabled

IGMP Snooping Source-only-learning enabled

Disablig IGMP Snooping Source-only-learning doesn't change anything. Commands show ip igmp snooping group

and show mac address-table multicast

don't list any ports. Receivers use IGMPv3. Please advise how to configure IGMP snooping on 2950.

Thanks

Jon Marshall · ‎10-01-2009

IGMP snooping works by the switch listening to the answer to IGMP queries ie. something has to make IGMP queries.

If the switch supports the IGMP querier function then the switch can make the IGMP queries. But if that function does not exist on the switch then for the switch to learn dynamic multicast groups with IGMP snooping you will have to have a router connected to the switch.

If the switch is standalone and does not support the IGMP querier function then IGMP snooping will not work and the multicast packets would be flooded to all ports unless as you have already done you configure static entries.

Jon

View solution in original post

glen.grant · ‎09-30-2009

https://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_22_ea11x/configuration/guide/swigmp.html

Ronyn____ · ‎10-01-2009

Thank you for the post. I have no experience with multicast. This switch is stand alone. With the configuration described in the first post the switch doesn't learn multicast group dynamically. The only time when the switch performs IGMP snooping is when the static association is configured. This can be explained: the switch floods unknown multicast traffic. As soon as static association is configured the traffic becomes known for the switch and can be filtered. The question is: how to configure dynamic association? There is no option for IGMP querier configuration.

Jon Marshall · ‎10-01-2009

IGMP snooping works by the switch listening to the answer to IGMP queries ie. something has to make IGMP queries.

If the switch supports the IGMP querier function then the switch can make the IGMP queries. But if that function does not exist on the switch then for the switch to learn dynamic multicast groups with IGMP snooping you will have to have a router connected to the switch.

If the switch is standalone and does not support the IGMP querier function then IGMP snooping will not work and the multicast packets would be flooded to all ports unless as you have already done you configure static entries.

Jon

Ronyn____ · ‎10-01-2009

Jon

Thanks for your post. This is the answer that I expected to get.