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By now, the subsequent multicast data flows to RP 2 along the SPT, and then from RP 2 to the
receiver-side DR along the RPT. After receiving the multicast data, the receiver-side DR
determines whether to initiate an RPT-to-SPT switchover process based on its configuration.
{ If no receivers exist in the domain, RP 2 neither creates an (S, G) entry nor sends a join message
toward the multicast source.
In inter-domain multicasting using MSDP, once an RP gets information about a multicast source in another
PIM-SM domain, it no longer relies on RPs in other PIM-SM domains. The receivers can override the RPs
in other domains and directly join the multicast SPT rooted at the source.
Anycast RP through MSDP
PIM-SM requires only one active RP to serve each multicast group. If the active RP fails, the multicast traffic
might be interrupted. The Anycast RP mechanism enables redundancy backup among multiple RPs by
configuring the RPs with the same IP address for one multicast group. A multicast source registers with the
closest RP or a receiver joins the closest RP to implement source information synchronization.
Anycast RP has the following benefits:
• Optimal RP path—A multicast source registers with the closest RP to build an optimal SPT. A receiver
joins the closest RP to build an optimal RPT.
• Redundancy backup among RPs—When an RP fails, the RP-related multicast sources and
receiver-side DRs register with or join the closest available RP. This achieves redundancy backup
among RPs.
Anycast RP can be implemented through MSDP by configuring multiple RPs with the same IP address for
one multicast group and establishing MSDP peering relationships among the RPs.
As shown in Figure 5
2, within a PIM-SM domain, a multicast source sends multicast data to multicast
group G, and the receiver joins the multicast group.
To implement Anycast RP:
1. Configure the same IP address (known as Anycast RP address, typically a private address) to an
interface on Router A and Router B.
{ An Anycast RP address is usually configured on a logical interface, such as a loopback
interface.
{ Make sure the Anycast RP address is a host address (with the subnet mask 255.255.255.255).
2. Configure these interfaces as C-RPs.
3. Establish an MSDP peering relationship between Router A and Router B. An MSDP peer address
must be different from the Anycast RP address.