3Com MSR 50 Series Configuration Manual page 1135

Figure 335 Diagram for RPF check for SA messages
Source
RP 1
AS 1
(1)
(2)
RP 2 RP 3
AS 2
MSDP peers
Static RPF peers
SA message
As illustrated in Figure
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 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)
Although RP 4 and RP 5 are in the same SA (AS 3) and both are MSDP peers of RP
6, because RP 5 has a higher IP address, RP 6 accepts only the SA message from RP
5.
5 When RP 7 receives the SA message from RP 6
Because the SA message is from a static RPF peer (RP 6), RP 7 accepts the SA
message and forwards it to other peer (RP 8).
6 When RP 8 receives the SA message from RP 7
RP 5
(3)
Mesh group
AS 3
(3)
RP 4
335, these MSDP peers dispose of SA messages according
MSDP Overview
RP 9
(7)
AS 5
(4)
(5)
(4)
RP 6
AS 4
1135
RP 8
(6)
RP 7