Multicast Source Discovery Protocol (MSDP) is an inter-domain multicast solution that applies to interconnected multiple Protocol Independent Multicast-Sparse Mode (PIM-SM) domains. Currently, MSDP applies only to IPv4.
A network composed of PIM-SM devices is called a PIM-SM network. In real-world situations, a large PIM-SM network may be maintained by multiple Internet service providers (ISPs).
A PIM-SM network uses Rendezvous Points (RPs) to forward multicast data. A large PIM-SM network can be divided into multiple PIM-SM domains. On a PIM-SM network, an RP does not communicate with RPs in other domains. An RP knows only the local multicast source's location and distributes data only to local domain users. A multicast source registers only with the local domain RP, and hosts send Join messages only to the local domain RP. Using this approach, PIM-SM domains implement load splitting among RPs, enhance network stability, and facilitate network management.
After a large PIM-SM network is divided into multiple PIM-SM domains, a mechanism is required to implement inter-domain multicast. MSDP provides this mechanism, enabling hosts in the local PIM-SM domain to receive multicast data from sources in other PIM-SM domains.
In this section, a PIM-SM domain refers to the service range of an RP. A PIM-SM domain can be a domain defined by bootstrap router (BSR) boundaries or a domain formed after you configure static RPs on the router.