Multicast and the RPF logic

Answered Question
Nov 6th, 2007

Dear friends,

I'm studying multicast. While I was reading a book, I saw this: "A multicast router can have more than one interface in the outgoing interface list, but it can have only one interface in the incoming interface list.".

The excerpt above is talking about the "show ip mroute" command.

The question is: what if I have to routes to the same source of multicast traffic - let's say, through two different interfaces using the same cost? I'll have two routes in my unicast routing table, right?

How can PIM handle this? Will it choose one of them and discard the other one?

Cheers,

Mauricio

I have this problem too.
0 votes
Correct Answer by ankbhasi about 9 years 1 month ago

Hi Mauricio,

These doubts are obvious to come when you start reading multicast. Keep going ahead and you will come to know across the way PIM take different decisions.

For now coming to your doubt you can read these 2 links and I am sure you will be clear about many stuff

http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml#equalcostpaths

Read section 2.9 from this link

http://tools.ietf.org/html/rfc2362

Please come back if you have any doubts.

HTH

Ankur

*Pls rate all helpfull post

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nambi_gct Tue, 11/06/2007 - 06:48

Hi Mauricio,

In this case the router with the highest ip address will be chosen as rpf neighbor.

Thanks

Nambi

Correct Answer
ankbhasi Tue, 11/06/2007 - 08:16

Hi Mauricio,

These doubts are obvious to come when you start reading multicast. Keep going ahead and you will come to know across the way PIM take different decisions.

For now coming to your doubt you can read these 2 links and I am sure you will be clear about many stuff

http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml#equalcostpaths

Read section 2.9 from this link

http://tools.ietf.org/html/rfc2362

Please come back if you have any doubts.

HTH

Ankur

*Pls rate all helpfull post

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