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How CGMP/IGMP Snooping enabled switches behave when a multicast source

Hello all,

I have a trivial question about multicast behaviour.

I have found a lot of documents on how CGMP/IGMP snooping enabled switches behave when a receiver wants to join a multicast group (IGMP join report ..etc)

I would like to know what happens when a source host starts sending a multicast stream. How does a switch understand to send it just to the multicast router (I guess because it reads some IGMP report packets).

What happen on other ports. Will the multicast traffic flood to all other local ports ?

As far as I know a multicast source does not use any signalling protocol (IGMP)

Am I wrong ?

Cheers

1 REPLY

Re: How CGMP/IGMP Snooping enabled switches behave when a multic

Hi,

Generally a source would send them in PIM register messages which if you look at a switches CAM table has the associated MAC address of 224.0.0.13 is swithced to CPU and Router port and hence know's the source of the PIM.

Here is a extract from a 6k doing a sh cam sys:

9 01-00-5e-00-00-0d # 1/3 = PIM

9 01-00-5e-00-00-16 # 1/3 = IGMP

Regards

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