multicast join question

[gongya001]

Two RPs are configured as follows:

ip pim rp-candidate Loopback0

ip pim bsr Loopback0 0 100

R1 and R2 mutually redistribute ospf and bgp.

239.6.6.6 should join both RPs? 

I do not need MSDP in this scenario to make multicast group available to both AS domain, right ?

[willwetherman · Accepted solution]

Hi,

The edge routers can only use a single RP for a specific multicast group for both multicast source registrations and receiver joins. If the multicast sources and receivers all use the same RP for the same multicast group then MSDP is not required. However, if sources and receivers are using different RPs for the same multicast group, then MSDP is required to allow the sources and receivers to correctly locate each other.

In your scenario, assuming ip pim bsr-border is not configured on the interfaces connecting the two RPs, all of the edge routes will learn of both RPs. As both RPs are advertised with the same priority value of 100, the highest RP IP address will be used as the tie-breaker, which in your scenario, will be R2. As a result, multicast source registration and receiver joins for group 239.6.6.6 will use RP R2 so MSDP will not be required.

If you configure ip pim bsr-border between the RPs, then BSR information will not be propagated between the domains resulting in the edge routers in each domain to learn of their local RP only. MSDP will be required in this situation.

I hope that this helps

Will

[gongya001]

thanks so much !!