Rendezvous Points
A rendezvous point (RP) is a role that a device performs when operating in Protocol Independent Multicast (PIM) Sparse Mode
(SM). An RP is required only in networks running PIM SM. In the PIM-SM model, only network segments with active receivers
that have explicitly requested multicast data will be forwarded the traffic. This method of delivering multicast data contrasts
with PIM Dense Mode (PIM DM). In PIM DM, multicast traffic is initially flooded to all segments of the network. Routers that
have no downstream neighbors or directly connected receivers prune back the unwanted traffic. An RP acts as the meeting place
for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic
is then forwarded to receivers down a shared distribution tree.
By default, when the first hop device of the receiver learns about the source, it will send a Join message directly to the
source, creating a source-based distribution tree from the source to the receiver. This source tree does not include the RP
unless the RP is located within the shortest path between the source and receiver. In most cases, the placement of the RP
in the network is not a complex decision.
By default, the RP is needed only to start new sessions with sources and receivers. Consequently, the RP experiences little
overhead from traffic flow or processing. In PIM version 2, the RP performs less processing than in PIM version 1 because
sources must only periodically register with the RP to create state.