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Community Member

Catalyst L2 Multicast Forwarding Table Question

Does the dynamically created entries in the L2 multicast forwarding table, made by IGMP Snooping expire, and if so, what is the interval or maxage? Also how does it work with 'response suppression' in IGMPv2, so that each group member can retain their membership, if only one member replies to a query?

Community Member

Re: Catalyst L2 Multicast Forwarding Table Question

With IGMP snooping, the switch does not forward replies to membership

queries out every port, so each group member has to respond to the query.

The switch will forward one of the replies to the router. In other words, igmp

snooping stops response suppression from working.

Multicast cam entries are not timed out, they're removed when the client attached to sends a leave (if you've got fast leave enabled), or after the

switch receives no replies to a group specific query sent out the port after

a leave has been received on that port (if you don't have fast leave enabled).

If clients do not send leaves (and just about every client should), the switch will remove the port once it stops receiving replies to normal igmp querys.

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