Configuring the Content of an SA Message
Context
The interval for sending multicast data by some multicast sources is longer than the aging time of (S, G) entries. In this case, the source designated router (DR) can only encapsulate multicast data into Register messages, and send the messages to the source rendezvous point (RP). The source RP transmits (S, G) information contained in Source-Active (SA) messages to the remote RP. Then the remote RP sends an (S, G) Join message to the source DR and creates an SPT. The remote RP cannot receive multicast data sent by this source because the (S, G) entry is aged out.
After the function of encapsulating a multicast packet in an SA message is enabled on a source RP, the source RP encapsulates a multicast packet in an SA message and sends the message out. After receiving the SA message, the remote RP decapsulates it and transmits the multicast packet along RPT to users in the local domain.
- When the RP creates an SA message for the first time, it checks the TTL value of the IP header in the multicast packet. If the value is smaller than the threshold, the RP does not create an SA message. If the value is equal to or larger than the threshold, the RP encapsulates the multicast packet in an SA message and forwards the message to an MSDP peer.
- When the RP receives an SA message that contains the multicast packet, it reduces the TTL value in the IP header by 1 and checks the TTL value. If the value is smaller than the threshold, the RP does not forward the SA message to any MSDP peer. If the value is equal to or larger than the threshold, the RP forwards the SA message to an MSDP peer.
Procedure
- Run system-view
The system view is displayed.
- Run msdp [ vpn-instance vpn-instance-name ]
The MSDP view is displayed.
- Run encap-data-enable
The function of encapsulating multicast data packets in SA messages is enabled.
- (Optional) Run peer peer-address minimum-ttl ttl
The TTL value of multicast data packets is set.
By default, the TTL value of multicast data packets is set to 0.