Core Issue
Auto-Rendezvous Point (RP) provides administrators a way to distribute group-to-RP mappings within a multicast network without having to manually configure static RPs on every router.
To accomplish this, auto-RP uses these mechanisms:
- Candidate RPs (C-RPs) send RP announcements to multicast group 224.0.1.39.
- Mapping agents receive the RP announcements from C-RPs. They decide which should be the RP for any given group (or groups) based on the highest IP address. The mapping agents then distribute that information to all multicast routers to the auto-RP multicast group 224.0.1.40. This is done using using RP discovery messages.
The sending of both RP announcements and RP discovery messages occurs every 60 seconds by default with a holdtime of 180 seconds. If no RP is found, the next search is done locally on each router for a static RP mapping. If no static RP mapping is configured, the router defaults to dense mode.
An improperly-configured ip pim rp-announce-filter command may result in RP announcements being ignored. In addition, issuing the ip pim rp-announce-filter command on any other router but the mapping agent itself fails. This is because non-mapping agents do not listen to group 224.0.1.39. Even if non-mapping agents were to receive these messages, they still would not distribute the necessary group-to-RP mappings to everyone on the shared tree because they would not know what to do with them.
Resolution
To resolve this issue, check the Protocol Independent Multicast (PIM) auto-RP mapping agent router for the ip pim rp-announce-filter command. Make sure the correct filters are set.
For detailed information regarding the command, refer to IP Multicast Routing Commands.
