Fwd: More Multicast Understanding

 Dear Experts,

I understand that the DR from the server side, is the 1st router receiving
the stream or in case of two routers one will be elected,and this router is
the one that informs the RP that a stream exists (Register message),and the
RP will send a register stop. On the client side,I understand that one of
the two routers on the segment is supposed to communicate with the RP
informing it that a client wants to listen to a certain group.

The thing that is confusing me is from an article I read, I understood that
the forwarder on a segment will be elected based on:
1)Best Administrative Distance to the souce
2)Best Metric to the source
3)Highest IP address.

Scenario:
 PIM SPARSE MODE (RP on loopback of BB1)
R1(STREAMER) -->LAN 1
BB1-->LAN 1
BB2-->LAN 1

BB1-->LAN 2
BB2-->LAN 2
R4(CLIENT)-->LAN 2

1)When everything was left at its default.BB2 was the one forwarding on the
segment,and this makes perfect sense since both BB1 and BB2 are connected to
the stream (Same AD,Same Metric), so what determined the forwarder was the
highest IP address (BB2).

2)When I used the command ip pim dr-priority <255> on BB1, the pim neighbor
relationship was re-established and BB1 was the one forwarding on the
segment. I used to think that the DR is only responsible for communicating
with the RP and is not the one who will forward on the segment. I thought
that the forwarder only depends on the 3 stated rules above. When I gave BB2
a higher priority (ip pim dr-priority 256) it began forwarding again and BB1
stopped forwarding.

This is what is confusing me.

I would be grateful if you can help me.

Best Regards,

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Received on Fri Oct 16 2009 - 16:12:31 ART