Content

| 7.3 |  | Routing Multicast Traffic |
| 7.3.13 |  | Configure auto-RP (optional) |

Manually configuring multiple rendezvous points in a large campus network can result in inconsistent RP configurations and can cause connectivity problems. Auto-RP is a Cisco proprietary standalone protocol that automates the distribution of group-to-RP mappings in a network running sparse-mode PIM. Auto-RP facilitates the use of multiple RPs within a network to serve different group ranges. Auto-RP also allows load splitting among different RPs and arrangement of RPs according to the locations of group participants. (With the auto-RP mechanism, an RP announce command must be entered on the router to act as an RP for a certain range of multicast group addresses. Multiple RPs can be used to serve different group ranges, or as backups of each other. An RP mapping agent is assigned to a router to receive the RP-announcement messages. The RP mapping agent then sends the consistent group-to-RP mappings to all designated routers. This method allows all designated routers to automatically discover which RP to use for attached receivers and senders.

Auto-RP is disabled by default. To enable auto-RP on a router, enter the following command in global configuration mode.

> Router(config)#ip pim send-rp-announce type number scope ttl group-list access-list-number

To disable a router as a candidate RP, enter the no ip pim send-rp-announce command. Candidate RPs send an auto-RP RP announcement message to the well-known group CISCO-RP-ANNOUNCE (224.0.1.39). A router configured as an RP-mapping agent listens on this well-known group address to determine which RPs act for the various ranges of multicast group addresses.

The RP mapping agent then sends the RP-to-group mappings in an auto-RP RP discovery message to the well-known group CISCO-RP-DISCOVERY (224.0.1.40). PIM DRs listen to this well-known group to determine which RPs to use.

By default, a router is not configured as a PIM RP mapping agent. To configure a router to send auto-RP RP discovery messages, enter the following command in global configuration mode.

> Router#(config)ip pim send-rp-discovery scope ttl

Where ttl is the TTL value that limits the scope of the discovery message.

The following example shows that Router 172.16.2.146 is an RP mapping agent. The scope of the discovery messages is 16 router hops.

> hostname Router
> !ip multicast-routing
> !(text deleted)
> ip pim send-rp-discovery scope 16

To disable a router as an RP mapping agent, enter the no ip pim send-rp-discovery command.