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RPT building
Figure 43 RPT building in a PIM-SM domain
As shown in
, 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 travels 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. At the same time, the upstream router checks
for the existence of receivers for that multicast group. If no receivers for the multicast group exist, 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
