This document specifies the Bootstrap Router (BSR) mechanism for the class of multicast routing protocols in the PIM (Protocol Independent Multicast) family that use the concept of a Rendezvous Point as a means for receivers to discover the sources that send to a particular multicast group. BSR is one way that a multicast router can learn the set of group-to-RP mappings required in order to function. The mechanism is dynamic@ largely self-configuring@ and robust to router failure.