HP 4800G Series Configuration Manual page 878

Figure 1-3 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 1-3, 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 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 AS (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
A BGP or MBGP route exists between two MSDP peers in different ASs. Because the SA message is
from an MSDP peer (RP 7) in a different AS, and the MSDP peer is the next hop on the BGP or MBGP
route to the source-side RP, RP 8 accepts the message and forwards it to its other peer (RP 9).
7) When RP 9 receives the SA message from RP 8
Because RP 9 has only one MSDP peer, RP 9 accepts the SA message.
RP 5
(3)
(4)
Mesh group
AS 3
(3)
(4)
RP 4
1-5
RP 9 RP 8
(7)
AS 5
(6)
(5)
RP 6 RP 7
AS 4