A VPN instance can support MSDP. To be specific, between the interfaces of the same instance on a multicast router (public network instance or VPN instance), the MSDP peer relationship can be set up, and then MSDP peers exchange Source Active (SA) messages to implement inter-domain VPN multicast.
A multicast router on which multi-instance is applied maintains a set of MSDP mechanism for each instance, including SA cache, peer connection, timer, sending cache, and the cache area for exchanging PIM information. At the same time, the multicast router isolates information between different instances. In this manner, only MSDP information and PIM-SM information of the same instance can be exchanged.