Users Guide
IPv4 and IPv6 Multicast 1531
PIM-SM Protocol Operation
This section describes the workings of PIM-SM protocol per RFC 4601. The
protocol operates essentially in three phases, as explained in the following
sections.
Phase-1: RP Tree
Figure 44-1. PIM-SM Shared Tree Join
• In this example, an active receiver (attached to leaf router at the bottom of
the drawing) has joined multicast group “G”.
• The leaf router (labeled DR above) knows the IP address of the
Rendezvous Point (RP) for group G and sends a (*, G) Join for this group
towards the RP.
• This (*, G) Join travels hop-by-hop to the RP, building a branch of the
Shared Tree that extends from the RP to the last-hop router directly
connected to the receiver.
• At this point, group “G” traffic can flow down the Shared Tree to the
receiver.