By default, a Source Active (SA) message contains only (S, G) information, with no multicast data packets encapsulated. You can configure multicast data encapsulation for an SA message on the source Rendezvous Point (RP) configured with an MSDP peer.
Before encapsulating a multicast data packet in an SA message, complete the following tasks:
The time during which certain multicast sources send multicast data is long, and is longer than the timeout of an (S, G) entry. In this case, the source Designated router (DR) encapsulates multicast data packets in Register messages one by one, and sends the messages to the source RP. The source RP then uses Source Active (SA) messages to forward (S, G) entries to the remote RP. The remote RP then sends a Join message to the source DR. A shortest path tree (SPT) is set up. Because of the timeout of the (S, G) entry, remote users cannot receive multicast data sent by multicast source S.
After the function of encapsulating a multicast packet in an SA message is enabled on the source RP, the source RP encapsulates multicast data in SA messages and sends them out. Once an SA message is received, a remote RP decapsulates the message and forwards the multicast data to users in the domain along the RPT.
msdp [ vpn-instance vpn-instance-name ]
By default, the SA message contains only (S, G) information, and does not contain a multicast data packet.