What is PIM Sparse Mode?
PIM sparse mode is more efficient when you have relatively few listeners for any given multicast stream. It saves bandwidth over Dense mode but is much more complex and requires a central router called a Rendezvous Point or RP to arbitrate traffic flow. When a receiver wants to receive traffic from a particular multicast group it sends a Join message toward the RP. This builds up a multicast path called the shared tree from the RP to the receiver as it travels toward the RP. When a source begins to transmit on a group the directly connected router initially encapsulates the packet in a Register message and sends it via Unicast to the RP. The RP sends the encapsulated multicast traffic down the shared tree to any listeners that have already joined. The RP also sends a join toward the sender to extend the shared tree to it. Now all traffic is flowing from sender to all receivers, although it is all passing through the RP rather than taking the most efficient path. If the bandwidth used b
