Im not particularly confident with multicast as its something I have not ye had to configure professionally, so these notes are a bit scatty as I try to get grips with some of it.

Finding the RP using Boost Strap Router (BSR) -
If multiple BSR configured routers exist in a network an election will take place and the one with the highest priority will win then the highest IP address used as a tie breaker. The winner is elected the preferred BSR, this is performed by each router advertising itself until a “better” BSR is discovered. Another election will also take place if a BSR does not receive a BSR message within 150 seconds. The preferred BSR will forward messages but BSRs which were not selected as the preferred BSR will monitor BSR messages but not originate them.

The BSR will be advertised in a BSR bootstrap messages which is forwarded out of all non-RPF interfaces by every router to the all PIM routers multicast group 224.0.0.13 with a TTL of 1, each router in turn resets the TTL to 1, thereby the messages should be received by every router on the network. This alleviates the chicken and egg issue with Auto RP in PIM-SM. Once candidate RPs are aware of the BSR they will announce themselves to the BSR via unicast, and then BSR will advertise this information of all the RPs bootstrap message to all PIM routers, it is then up to each router to decide which RP to use.

To configure BSR, first setup one or more candidate BSRs with the command;

Router(config)#ip pim bsr-candidate {interface} [Hash Mask 0-32] [Priority 0-255]

As with Auto RP you will also need to configure candidate RPs with the command

Router(config)#ip pim rp-candidate [interface] [group-list] [interval] [priority]

Anycast RP with Multicast Source Discovery Protocol (MSDP) – This approach to assisting routers finding the RP is not an independent protocol and can be used with, Auto RP or BSR. Anycast RP Its a relatively simple, firstly Anycast RP need to be configured, this is where multiple mapping Agents or BSRs in the network uses the same IP address. Eg if 3 Auto RP mapping agents were configured with the address 10.0.0.1 and this was advertised into the IGP each router would take the shortest path to get to its nearest Auto RP mapping agent as determined by the IGP. This has the nice benefits of failover in the time it takes for the IGP to reconverge and load balancing.

But there is a problem with Anycast RP a source may register with one RP and its receivers may join a separate RP, so MSDP was developed to allow RPs to exchange information about active sources with each other. MSDP routers are configured as peers and communicate with each other when a source sends a SA message for a multicast group, thereby every MSDP peer will becomes aware of the sources for each multicast group in other areas of the network where they are not the nearest RP. In case of failure the IGP will handle putting the receivers in contact with another Auto RP mapping agent or BSR in the convergence time for the IGP.

Please report any glaring mistakes in the above if you spot any, cheers!