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How does a PIM-SSM LHR select the multicast source ?

[ Edited ]
3 weeks ago

Hello Experts.

 

An IGMP v3 Report message may not be specific about a single source for a requested multicast stream. It may have an INCLUDE source list that contains a list of sources from which any one source would do. Or it may have an EXLUDE source list that contains a list of sources it does NOT want traffic from (any other source would do). 

 

I have two related questions.

Question 1:

If a PIM SSM router receives an IGMPv3 REPORT for group G with an EXCLUDE source list of S1, how does the router decide on a source to send a PIM JOIN to?

 

Question 2:

If a PIM SSM router receives an IGMPv3 REPORT for group G with an INCLUDE source list of S1, S2  how does it decide which of the two sources to send a PIM JOIN to?

 

Many thanks,

Deepak

3 REPLIES 3
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Re: PIM-SSM LHR selection from the IGMPv3 source list.

3 weeks ago

Hi,

 

The SSM protocol mandates that when IGMPv3 join is received on the LHR it will send out PIM join directly to the source IP of S1.

This router LHR would have PIM neighbor ship and hence unicast route to the FHR connected to S1.

Similarly if you have S1 and S2 the PIM join from LHR will be sent directly to FHR for S1 or FHR of S2 depending on the source ip in the IGMP join message.

 

Hope this helps

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Re: PIM-SSM LHR selection from the IGMPv3 source list.

3 weeks ago

Hi raviky

 

Thanks for your response.

 

An IGMPv3 Report message can contain several sources. In this case, which source will the LHR choose?

 

Thanks,

Deepak

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Re: PIM-SSM LHR selection from the IGMPv3 source list.

3 weeks ago

Hi Deepak,

 

I believe when we have multiple sources in an SSM you will have multiple source based tree formed from the LHR to each source. This is because in SSM we need to have the shortest path source rooted tree and hence for each different source we will have the different source based tree. The source selection will depend on the IGMPv3 feature (INCLUDE/EXLUDE) which determines which source to be included to form the tree and which ones to ignore.

 

 

 

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