A Rendezvous Point Mapping Agent joins the multicast group 224.0.1.39 to receive rendezvous point advertisements.
When an announcement has been received, it will store it in a group to rendezvous point mapping cache along with a hold timer. If there are multiple of the same group range advertised, the candidate rendezvous points advertisement with the highest IP address will be selected and stored.
The mapping agents advertise their stored mappings in the cache to another multicast address, 224.0.1.40, the Cisco rendezvous point discovery address.
The messages are advertised every 60 seconds or when a change in the cache is detected. The mapping agents advertisements contain the elected rendezvous points and their group to rendezvous point mappings.
PIM enabled routers listen on the multicast address 224.0.1.40 and will store these rendezvous point mapping messages in their own caches.
Multiple mapping agents can be configured on the same network to provide a backup in case of a network failure. Mapping agents act independently with no mechanism to elect a primary mapping agent between them – they will all advertise their own collected cache information on the multicast address 224.0.1.40
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