.254 DR .253
2 PIM-SM routers .254 and .253 only the DR .254 sends Joins to the RP to build the shared-tree….
If HOST sources multicast, the DR sends Register messages to the RP….
.254 and .253 both start receiving multicast traffic from the same source RP (source is upstream from the RP say), this triggers both to send PIM Assert messages to determine forwarder, PIM Assert determine if all the routers are running the same unicast protocol, the router with the best metric wins the Assert. If the metrics are equal, the router with the highest IP address is elected. Then .253 will prune and only .254 will send….