Overview of MSDP

Multicast Source Discovery Protocol (MSDP) is an inter-domain multicast protocol that sets up an MSDP peer relationship between Rendezvous Points (RPs) in different PIM-SM domains. MSDP peers exchange (S, G) information by sending SA messages, so that the MSDP peers can share multicast source information and hosts can receive multicast data from sources in another PIM-SM domain.

Generally, a multicast source registers only with the RP in the local PIM-SM domain. Multicast source information is isolated between domains and therefore an RP knows only the multicast source in the local domain and sets up an MDT only for hosts in the local domain.

Therefore, MSDP is needed to transfer information about multicast sources of other domains to the RP in the local domain. The RP in the local domain can then send Join messages to the multicast sources of other PIM-SM domains and set up MDTs between the local domain and remote domains. In addition, multicast data packets can be transmitted across domains and the group members in the local domain can receive multicast data sent by the multicast sources in other domains.

MSDP peers set up TCP connections and perform the RPF check on received Source Active (SA) messages.

MSDP applies only to the Any-Source Multicast (ASM) model in PIM-SM.

MSDP can set up peer relationships between RPs in the same PIM-SM domain, so that the RPs can share multicast source information to implement Anycast-RP.