IGMP and conference call issue

Unanswered Question
Dec 8th, 2008

Dear All,

I have a customer reported that they have some problem for conference call, one to one call is O.K., however, when multiple user join conference call, it's getting problem, customer requested to enable IGMP on the router, could you please guide what's the good point here to enable IGMP? or any good documentation for IGMP and voice will be great!

Thank you so much.

I have this problem too.
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Giuseppe Larosa Mon, 12/08/2008 - 23:40

Hello Trina,

your customer thinks that the conference call being a multipoint service can be mapped over an IP multicast address.

If this is the case they are right but you may need to enable multicast routing on your router

ip multicast-routing

on each interface that can be source, destination or transit for multicast traffic

ip pim sparse-dense-mode

note: this will also enable igmp on lan interfaces automatically

for more info see

for an introduction to multicast see from 12.4 multicast conf guide:


Hope to help



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