3Com 7757 Configuration Manual page 484

484 C 48: MSDP C
HAPTER
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ONFIGURATION
5 Upon receiving the SA message created by RP 1, RP 2 in PIM-SM 2 checks whether
there are any receivers for the multicast group in the domain.
If so, the RPT for the multicast group G is maintained between RP 2 and the
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receivers. RP 2 creates an (S, G) entry, and sends an (S, G) join message hop by
hop towards 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 is forwarded by RP 2 to the receivers along
the RPT. Upon receiving the multicast traffic, the DR at the receiver side (DR 2)
decides whether to initiate an RPT-to-SPT switchover process.
If no receivers for the group exist in the domain, RP 2 does dot create an (S, G)
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entry and does not join the SPT rooted at the source.
An MSDP mesh group refers to a group of MSDP peers that have MSDP
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peering relationships among one another and share the same group name.
When using MSDP for inter-domain multicasting, once an RP receives
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information from 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 122, there are five autonomous systems in the network, AS 1
through AS 5, with IGP enabled on routers within each AS and EBGP 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.
If only one MSDP peer exists in a PIM-SM domain, this PIM-SM domain is also
called a stub domain. For example, AS 4 in Figure 122 is a stub domain. The MSDP
peer in a stub domain can have multiple remote MSDP peers at the same time.
You can configure one or more remote MSDP peers as static RPF peers. 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 122 Diagram for RPF check for SA messages
Source
RP 1
AS 1
(1)
(2)
RP 2
AS 2
MSDP peers
Static RPF peers
SA message
RP 5
(3)
Mesh group
AS 3
RP 3
(3)
RP 4
RP 9
(7)
AS 5
(4)
(5)
(4)
RP 6
AS 4
RP 8
(6)
RP 7