3.2.c [i] Intra-domain MSDP [anycast RP]
PIM-SM is the multicast forwarding protocol used in the intra-domain multicast scenarios. Anycast RP is a useful application of MSDP. This technique is used for configuring a multicast sparse mode network to provide for fault tolerance and load sharing within a single multicast domain.
Two or more RPs are configured with the same IP address (for example, 220.127.116.11) on loopback interfaces. The loopback address should be configured with a 32-bit mask. All the downstream routers are configured so that they know that 18.104.22.168 is the IP address of their local RP. IP routing automatically selects the topologically closest RP for each source and receiver. Because some sources use only one RP and some receivers a different RP, a method is needed for the RPs to exchange information about active sources. This information exchange is done with MSDP. All the RPs are configured to be MSDP peers of each other . Each RP will know about the active sources in the area of the other RP. If any of the RPs were to fail, IP routing would converge and one of the RPs would become the active RP in both areas.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 2556-2564). . Kindle Edition.
3.2.c [ii] SA filter
MSDP-SA messages contain Source, Group (S, G) information for rendezvous points (RPs) (also known as MSDP peers) in PIM sparse-mode (PIM-SM) domains. This mechanism allows RPs to learn about multicast sources in remote PIM-SM domains so that they can join those sources if there are local receivers in their own domain. You can also use MSDP between multiple RPs in a single PIM-SM domain to establish MSDP mesh-groups. With a default configuration, MSDP exchanges SA messages without filtering them for specific source or group addresses.
Typically, there are a number of (S, G) states in a PIM-SM domain that should stay within the PIM-SM domain, but, due to default filtering, they get passed in SA messages to MSDP peers. Examples of this include domain local applications that use global IP multicast addresses , and sources that use local IP addresses (such as 10. x.y.z). In the native IP multicast Internet, this default leads to excessive (S, G) information being shared.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 2570-2573). . Kindle Edition.