IP Multicast Overview
For example, if there are 10 groups with 6 sources per group and 3 outgoing interfaces:
of (*,G)s x (380 + (# of OIL entries x 150)) = 10 x (380 + (3 x 150)) = 8300 bytes for (*,G)
of (S,G)s x (220 + (# of OIL entries x 150)) = 60 x (220 + (3 x 150))= 40,200 bytes for (S,G)
A total of 48,500 bytes of memory is required for the mroute table.
There are several methods for deploying RPs.
RPs can be deployed using a single, static RP. This method does not provide redundancy or load-balancing and is not recommended.
Auto-RP is used to distribute group-to-RP mapping information and can be used alone or with Anycast RP. Auto-RP alone provides failover, but does not provide the fastest failover nor does it provide load-balancing.
Anycast RP is used to define redundant and load-balanced RPs and can be used with static RP definitions or with Auto-RP. Anycast RP is the optimal choice as it provides the fast failover and load-balancing of the RPs.
In this document, the examples illustrate the most simplistic approach to Anycast RP by using locally-defined RP mappings.
Anycast RP is the preferred deployment model as opposed to a single static RP deployment. It provides for fast failover of IP multicast (within milliseconds or in some cases seconds of IP Unicast routing) and allows for load-balancing.
In the PIM-SM model, multicast sources must be registered with their local RP. The router closest to a source performs the actual registration. Anycast RP provides load sharing and redundancy across RPs in PIM-SM networks. It allows two or more RPs to share the load for source registration and to act as hot backup routers for each other (multicast only). Multicast Source Discovery Protocol (MSDP) is the key protocol that makes Anycast RP possible. MSDP allows RPs to share information about active sources.
With Anycast RP, the RPs are configured to establish MSDP peering sessions using a TCP connection. When the RP learns about a new multicast source (through the normal PIM registration mechanism), the RP encapsulates the first data packet in a Source-Active (SA) message and sends the SA to all MSDP peers.
Two or more RPs are configured with the same IP address on loopback interfaces. The Anycast RP loopback address should be configured with a 32-bit mask, making it a host address. All the downstream routers are configured to “know” that the Anycast RP loopback address is the IP address of their RP. The non-RP routers will use the RP (host route) that is favored by the IP unicast route table. When an RP fails, IP routing converges and the other RP assumes the RP role for sources and receiver that were previously registered with the failed RP. New sources register and new receivers join with the remaining RP.
Cisco AVVID Network Infrastructure IP Multicast Design