H3C Technologies H3C S12500 Series Switches - Manual (Page 205)

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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 (supposing that 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.
SA messages from paths other than those described previously will not be accepted or forwarded by
MSDP peers.
Intra-domain Anycast RP through MSDP
Anycast RP refers to 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 relationship between, these RPs.
The significance of Anycast RP is as follows:
• Optimal RP path—A multicast source registers with the nearest RP so that an SPT with the optimal
path is built. A receiver joins the nearest RP so that an RPT with the optimal path is built.
• Load balancing between RPs—Each RP needs to maintain just part of the source/group information
within the PIM-SM domain and forward part of the multicast data, thus achieving load balancing
between different RPs.
• Redundancy backup between RPs—When an RP fails, the multicast source previously registered on
it or the receivers that previously joined it will register with or join another nearest RP, achieving
redundancy backup between RPs.
As shown in Figure 58 , 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.
NOTE:
Usually an Anycast RP address is configured on a logic interface, like a loopback interface.