195
NOTE:
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.
RPF check rules for SA messages
As shown in
:
•
The autonomous systems in the network are AS 1 through AS 5. IGP is enabled on routers
within each AS and BGP or MBGP as the interoperation protocol among the 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 Diagram for RPF check for SA messages
As shown in
, 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:
The source-side RP address carried in the SA message is the same as the MSDP peer address.
This means that the MSDP peer where the SA is from is the RP that has created the SA
message. Therefore, 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:
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. Therefore, 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:
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. However, 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.
