H3C Technologies H3C S12500 Series Switches - Manual (Page 204)

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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 Figure 57 , the autonomous systems in the network are AS 1 through AS 5, with IGP 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 relationship 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.
NOTE:
When the switch receives an SA message from a static RPF peer, it 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 Figure 57 , 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 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