Multicast Source Discovery Protocol (MSDP) is designed to connect different PIM-SM multicast domains together in such a way that a multicast source can transmit to hosts in other PIM-SM domains. MSDP is not dependent on PIM-SM and can be used with other protocols as well. MSDP capable routers in one domain form a MSDN peering relationships with routers in other domains. Control information is exhanged over a TCP connection.