HP MSR2003 Configuration Manual page 94

RPT building
Figure 34 RPT building in a PIM-SM domain
Source
Server
As shown in
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 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 (*) represents 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. The prune message 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. It also checks whether it still 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.
RP
RPT
Join message
Multicast packets
Figure 34, the process of building an RPT is as follows:
DR
84
Host A
Receiver
DR
Host B
Receiver
Host C