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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
, the autonomous systems in the network are AS 1 through AS 5. IGP is enabled
on routers within each AS and BGP or MBGP as the interoperation protocol among the 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.
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
, these MSDP peers dispose of SA messages according to the following RPF check
rules:
1.
When RP 2 receives an SA message from RP 1:
Because the source-side RP address 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.
4.
When RP 6 receives the SA messages from RP 4 and RP 5 (suppose RP 5 has a higher IP address):
