Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 289
Rendezvous Points

PIM-SM uses specific routers known as the rendezvous point (RP) to start out the shared tree. Senders and receivers join a multicast group by registering at their rendezvous router. A rendezvous point is simply an IP address of a single router. These points are used by senders to announce themselves and for receivers to find out about new senders for a group.

Where and how is the RP found? There is one router in a single PIM domain (a contiguous set of routers that all implement PIM) called the bootstrap router (BSR). This router is responsible for sending out Bootstrap messages. The BSR is dynamically elected and distributes information about the RP. BSR information is sent to each router in the PIM domain. To find out about RPs, all routers within a PIM domain collect Bootstrap messages and store the information contained in the BSR messages.

If a router wishes to work as an RP, it becomes a candidate RP (C-RP). C-RPs send out Advertisement messages to the BSR for the domain. Inside the advertisements are the Group Address and the Group Mask (prefix) fields for which it can become the RP; in other words, what group address ranges it can support as an RP. This range can be one group to all groups. This allows the BSR to distribute RP information to other PIM routers in the domain using the All-PIM-Routers message.