3Com 5500-EI PWR Install Manual page 399

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 5-4, 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 5-4 Typical network diagram of Anycast RP
RP 1
Router A
Source
MSDP peers
SA message
The work process of Anycast RP is as follows:
1) The multicast source registers with the nearest RP. In this example, Source registers with RP 1,
with its multicast data encapsulated in the register message. When the register message arrives to
RP 1, RP 1 decapsulates the message.
RP 2
Router B
Receiver
PIM-SM
6