Source Active messages
In a PIM domain, MSDP enabled routers are RPs. MSDP routers form
adjacencies through TCP port 639 to share multicast source information.
This functionality is similar to the Border Gateway Protocol (BGP).
When an MSDP router receives multicast source information, the routers
use reachability information to perform Reverse Path Forwarding (RPF)
checks. The reachability information is exchanged through BGP or any
other unicast routing protocol.
When a RP router learns of a new (S,G), the RP router saves the (S,G) information and the RP
address in the MSDP Source Active (SA) local cache. The RP router learns the new (S,G)
through a directly connected source or PIM register message. The RP router then sends an
SA update message which contains (S,G,RP) information to the MDSP peers. The MSDP peers
broadcast the SA to RPs in their local domains and to their MSDP peers in other PIM-SM domains.
Note
A PIM domain is a set of routers in a single Autonomous System (AS), which uses
the same RP for any given multicast group.
When an SPB-PIM Gateway Controller in the SPB domain learns of a new (S,G) in its own domain, the
Controller saves the (S,G) information in the local SA cache. The Controller learns the
new (S,G) through a directly connected source or
Intermediate-System-to-Intermediate-System (IS-IS). The controller sends an SA update
message to the MSDP peers in the PIM domain. SA uses the CLIP address configured on the
controller as the RP address.
Note
Configure CLIP before you enable MSDP. Peer connections use the CLIP address as
the local address.
