Users Guide

Table Of Contents

1568 IPv4 and IPv6 Multicast

Phase-2: Register Stop

Figure 46-2. PIM-SM Sender Registration—Part1

• As soon as an active source for group G sends a packet, the designated

router (DR) that is attached to this source is responsible for “Registering”

this source with the RP and requesting the RP to build a tree back to that

router.

• To do this, the source router encapsulates the multicast data from the

source in a special PIM-SM message, called the Register message, and

unicasts that data to the RP.

• When the RP receives the Register message, it does two things:

– It de-encapsulates the multicast data packet inside of the Register

message and forwards it down the Shared Tree.

– The RP sends a source group (S, G) Join back towards the source to

create a branch of an (S, G) Shortest-Path Tree (SPT). This results in

the (S, G) state being created in the entire router path along the SPT,

including the RP.