H3C S5500-EI Configuration Manual page 233

In addition, you can configure MSDP peers into an MSDP mesh group so as to avoid flooding of
SA messages between MSDP peers.
An MSDP mesh group refers to a group of MSDP peers that have MSDP peering relationship
among one another and share the same group name.
SA messages are forwarded from one MSDP peer to another, and finally the information about the
4.
multicast source traverses all PIM-SM domains with MSDP peers (PIM-SM 2 and PIM-SM 3, in this
example).
After receiving the SA message that RP 1 created, RP 2 in PIM-SM 2 determines whether any
5.
receivers for the multicast group exist in the domain.
If receivers for the multicast group exist in the domain, the RPT for the multicast group G is
maintained between RP 2 and the receivers. RP 2 creates an (S, G) entry and sends an (S, G)
join message hop by hop toward DR 1 at the multicast source side, so that it can directly join
the SPT rooted at the source over other PIM-SM domains. Then, the multicast data can flow
along the SPT to RP 2 and RP 2 can forward the data to the receivers along the RPT. After
receiving the multicast traffic, the DR at the receiver side (DR 2) determines whether to initiate
an RPT-to-SPT switchover process.
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 60, the autonomous systems in the network are AS 1 through AS 5, with IGP enabled
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