HP 6125G Configuration Manual page 169

If no receivers for the group exist in the domain, RP 2 neither creates an (S, G) entry nor joins
the SPT rooted at the source.
NOTE:
When using MSDP for inter-domain multicasting, once an RP receives information form a multicast source,
it no longer relies on RPs in other PIM-SM domains. The receivers can override the RPs in other domains
and directly join the multicast source-based SPT.
RPF check rules for SA messages
As shown in
on routers within each AS and BGP or MBGP as the interoperation protocol among different ASs. Each
AS contains at least one PIM-SM domain, and each PIM-SM domain contains one or more RPs. MSDP
peering relationship has been established among different RPs. RP 3, RP 4, and RP 5 are in an MSDP
mesh group. On RP 7, RP 6 is configured as its static RPF peer.
NOTE:
When an RP receives an SA message from a static RPF peer, the RP accepts the SA message and forwards
it to other peers without performing an RPF check.
Figure 52 Diagram for RPF check for SA messages
As shown in
rules:
When RP 2 receives an SA message from RP 1:
1.
Because the source-side RP address carried in the SA message is the same as the MSDP peer
address, which means that the MSDP peer where the SA is from is the RP that has created the SA
message, RP 2 accepts the SA message and forwards it to its other MSDP peer (RP 3).
When RP 3 receives the SA message from RP 2:
2.
Because the SA message is from an MSDP peer (RP 2) in the same AS, and the MSDP peer is the
next hop on the optimal path to the source-side RP, RP 3 accepts the message and forwards it to
other peers (RP 4 and RP 5).
When RP 4 and RP 5 receive the SA message from RP 3:
3.
Figure 52, the autonomous systems in the network are AS 1 through AS 5, with IGP enabled
Figure 52, these MSDP peers dispose of SA messages according to the following RPF check
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