HP A8800 Configuration Manual page 202

An MSDP mesh group refers to a group of MSDP peers that have MSDP peering relationships among one
another and share the same group name.
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
enabled 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 relationships have 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.
After 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 57 Diagram for RPF check for SA messages
As illustrated in
check rules:
1. When RP 2 receives an SA message from RP 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).
2. When RP 3 receives the SA message from RP 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).
3. When RP 4 and RP 5 receive the SA message from RP 3, because the SA message is from an MSDP
peer (RP 3) in the same mesh group, RP 4 and RP 5 both accept the SA message, but they do not
forward the message to other members in the mesh group; instead, they forward it to other MSDP
peers (RP 6 in this example) out of the mesh group.
When RP 6 receives the SA messages from RP 4 and RP 5 (supposing that RP 5 has a higher IP
4.
address), although RP 4 and RP 5 are in the same AS (AS 3) and both are MSDP peers of RP 6, RP
6 accepts only the SA message from the MSDP with a higher IP address, that is, RP 5.
Figure 57, there are five autonomous systems in the network, AS 1 through AS 5, with IGP
Figure 57, these MSDP peers dispose of SA messages according to the following RPF
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