R21xx-HP FlexFabric 11900 IP Multicast Configuration Guide

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RPT building
Figure 28 RPT building in a PIM-SM domain
As shown in Figure 28, the process of building an RPT is as follows:
1. When a receiver wants to join the multicast group G, it uses an IGMP message to inform the
receiver-side DR.
2. After getting the receiver information, the DR sends a join message, which is forwarded hop by
hop to the RP that provides services for the multicast group.
3. The routers along the path from the DR to the RP form an RPT branch. Each router on this branch
adds to its forwarding table a (*, G) entry, where the asterisk (*) means any multicast source. The
RP is the root of the RPT, and the DR is a leaf of the RPT.
When the multicast data addressed to the multicast group G reaches the RP, the RP forwards the data to
the DR along the established RPT, and finally to the receiver.
When a receiver is no longer interested in the multicast data addressed to the multicast group G, the
receiver-side DR sends a prune message, which goes hop by hop along the RPT to the RP. After receiving
the prune message, the upstream node deletes the interface that connects to this downstream node from
the outgoing interface list and determines whether it has receivers for that multicast group. If not, the
router continues to forward the prune message to its upstream router.
Multicast source registration
The multicast source uses the registration process to inform an RP of its presence.
Source
Server
Host A
Host B
Host C
Receiver
Receiver
Multicast packets
RPT
Join message
RP DR
DR