3Com 4800G Series, Configuration Manual

Page: 677 / 1246

MSDP Overview 677
As illustrated in Figure 201, 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
An EBGP 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 EBGP 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.
SA messages from other paths than described above will not be accepted nor
forwarded by MSDP peers.
Implementing intra-domain Anycast RP by leveraging MSDP peers
Anycast RP refers to such an application that enables load balancing and
redundancy backup between two or more RPs within a PIM-SM domain by
configuring the same IP address for, and establishing MSDP peering relationships
between, these RPs.
As shown in Figure 202, within a PIM-SM domain, a multicast source sends
multicast data to multicast group G, and Receiver is a member of the multicast
group. To implement Anycast RP, configure the same IP address (known as anycast
RP address, typically a private address) on Router A and Router B, configure these
interfaces as C-RPs, and establish an MSDP peering relationship between Router A
and Router B.