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Community Member

Multiple sources for a single multicast group

Is it possible to have multiple sources for a single (i.e.same) multicast group in a pim environment.

If it is possible what are issues i might experience

Thanks in advance

7 REPLIES
Bronze

Re: Multiple sources for a single multicast group

There can be multiple sources for a single group. There should not be any issue as long as PIM discovers neighbors and builds the data distribution tree, and RPF check passes for the source.

Community Member

Re: Multiple sources for a single multicast group

Does this mean that there will be multiple multicast streams of the same group to the end receiver i.e. one from each source or will there only be one stream to the end receiver ?

Community Member

Re: Multiple sources for a single multicast group

The end station should be assigned to a multicast group which it is intersted in. To make it clear, the end station application should be configured with one multicast IP address which it would like to receive data from. Imagine the end station is your TV at home and the sources are all the channels out there.

Bronze

Re: Multiple sources for a single multicast group

Until the router directly connected to the receiver joins the SP-Tree (immediately by default on Cisco), you will receive multiple streams.

~Zach

Community Member

Re: Multiple sources for a single multicast group

How does the rp decide which source to take the multicast stream from ? If the same multicast group is being sent by multiple sources

How long would it take if the active source failed, for the next source of the same multicast group to take over ?

Bronze

Re: Multiple sources for a single multicast group

The RP doesn't. The RP joins the SP-Tree to each source router and forwards the traffic from both sources. The DR (the router directly connected to the receivers) initiates the SP-Tree join to the closest source, and then prunes itself from the RP-based shared tree.

~Zach

Community Member

Re: Multiple sources for a single multicast group

Hello,

Independent of whether the DR joins the shortest path tree towards the source, the IGMPv2 can only request a multicast group, it can't specify the source, so if using IGMPv2, and the PC requests group 225.100.100.99, and there are 20 sources sending to this group, the PC will receive traffic from all 20 sources. If you want the PC to select a group and a source you need IGMPv3.

Regards

Ian

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