Configuring SA message contents

Some multicast sources send multicast data at an interval longer than the aging time of (S, G) entries. In this case, the source-side DR must encapsulate multicast data packet-by-packet in register messages and send them to the source-side RP. The source-side RP transmits the (S, G) information to the remote RP through SA messages. Then, the remote RP sends join messages to the source-side DR and builds an SPT. Because the (S, G) entries have timed out, remote receivers can never receive the multicast data from the multicast source.

To avoid this problem, you can configure the source-side RP to encapsulate multicast data in SA messages. As a result, the source-side RP can forward the multicast data in SA messages to its remote MSDP peers. After receiving the SA messages, the remote RP decapsulates the SA messages and forwards the multicast data to the receivers in the local domain along the RPT.

The MSDP peers deliver SA messages to one another. After receiving an SA message, a router performs an RPF check on the message. If the router finds that the remote RP address is the same as the local RP address, it discards the SA message.

However, in the Anycast RP application, you must configure the same IP address for the RPs in the same PIM-SM domain and configure these RPs as MSDP peers. To make sure SA messages can pass the RPF check, you must assign SA messages a logical RP address that is different than the actual RP address. A logical RP address is the address of a logical interface on the router where the RP resides.

To configure the SA message contents: