3Com S7906E Configuration Manual page 1089

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.
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 1-4, 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.
Usually an Anycast RP address is configured on a logic interface, like a loopback interface.
Figure 1-4 Typical network diagram of Anycast RP
RP 1
Router A
Source
MSDP peers
SA message
The work process of Anycast RP is as follows:
RP 2
Router B
Receiver
PIM-SM
1-6