Auto-RP is a proprietary group discovery and mapping mechanism for IPv4 PIM that is described in cisco-ipmulticast/pim-autorp-spec, Auto-RP: Automatic discovery of Group-to-RP mappings for IP multicast. The functionality is similar to the IETF standard bootstrap router (BSR) mechanism that is described in RFC 5059, Bootstrap Router (BSR) Mechanism for Protocol Independent Multicast (PIM), to dynamically learn about the availability of Rendezvous Points (RPs) in a network. When a router is configured as an RP-mapping agent with the pim>rp>auto-rp-discovery command, it listens to the CISCO-RP-ANNOUNCE (224.0.1.39) group and caches the announced mappings. The RP-mapping agent then periodically sends out RP-mapping packets to the CISCO-RP-DISCOVERY (224.0.1.40) group. SR OS supports version 1 of the auto-RP specification, so the ability to deny RP-mappings by advertising negative group prefixes is not supported.
PIM dense-mode (PIM-DM) as described in RFC 3973, Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol Specification (Revised), is used for the auto-RP groups to support multihoming and redundancy. The RP-mapping agent supports announcing, mapping, and discovery functions; candidate RP functionality is not supported.
Auto-RP is supported for IPv4 in multicast VPNs and in the global routing instance. Either BSR or auto-RP for IPv4 can be configured; the two mechanisms cannot be enabled together. BSR for IPv6 and auto-RP for IPv4 can be enabled together. In a multicast VPN, auto-RP cannot be enabled together with sender-only or receiver-only multicast distribution trees (MDTs), or wildcard S-PMSI configurations that could block flooding.