Managing IPv4 and IPv6 Multicast 1175
• 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.
Phase-2: Register Stop
Figure 43-2. 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.
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