Using Anycast RP within PIM-SM domains is an implementation strategy that provides RP redundancy, rapid RP failover and RP load sharing
Anycast RP allows two or more RPs to share the load for source registration and the ability to act as hot backup routers for each other
MSDP is the key protocol in making Anycast RP possible, with all connected via it. This allows each RP to learn which sources have been registered with the other Anycast RPs in the domain.
The Anycast RP mechanism works as follows;
- Two or more routers are configured as the active RPs for the same group range at the same time. This would usually cause an error that would partition the PIM-SM domain. However MSDP is used to prevent this
- Each RP is assigned the same IP address. This I usually accomplished using a loopback interface. Each router advertises its RP address as a host route in the unicast routing protocol
- Leaf routers will use the closest RP based on their unicast routing table
Be careful that the loopback address used is not also used for the router ID (OSPF, BGP etc) as this will cause issue.
Recovery from a failed RP is quicker than Auto-RP or BSR. If an RP fails multicast traffic is only interrupted for the time it takes for the IGP to reconverge to the other RP with the same IP.
- Implementing Cisco Multicast (MCAST 2.0)
- Routing TCP/IP Volume II – Jeff Doyle
- Developing IP Multicast Networks, Volume I – Beau Williamson
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