Shared distribution trees and the rendezvous point
The Rendezvous Point (RP) is placed at a selected location that sees the traffic between the multicast source and the receiver groups. The RP maintains state for the respective groups. Multicast receivers initiate IGMP Join messages to their upstream router, which is named the designated router. The designated router forwards the packet to the RP.
In this model, the RP must be configured on all designated routers and must be reachable from those routers through a PIM-enabled interface.
Shared distribution trees consume much less memory than source distribution trees. At the same time, because a complete set of shortest paths is not maintained, the paths represented in a shared distribution tree may not be optimal and network latency may be greater than with a source tree.