HP 4800G Series Configuration Manual page 1014

configured RP or the RP dynamically calculated based on the BSR mechanism. The DR does not need
to know the RP address beforehand. The specific process is as follows.
At the receiver side:
1) A receiver host initiates an MLD report to announce its joining an IPv6 multicast group.
2) Upon receiving the MLD report, the receiver-side DR resolves the RP address embedded in the
IPv6 multicast address, and sends a join message to the RP.
At the IPv6 multicast source side:
1) The IPv6 multicast source sends IPv6 multicast traffic to the IPv6 multicast group.
2) The source-side DR resolves the RP address embedded in the IPv6 multicast address, and sends
a register message to the RP.
RPT establishment
Figure 1-5 RPT establishment in an IPv6 PIM-SM domain
As shown in Figure 1-5, the process of building an RPT is as follows:
1) When a receiver joins IPv6 multicast group G, it uses an MLD report message to inform the directly
connected DR.
2) Upon getting the IPv6 multicast group G's receiver information, the DR sends a join message,
which is hop by hop forwarded to the RP corresponding to the multicast group.
3) The routers along the path from the DR to the RP form an RPT branch. Each router on this branch
generates a (*, G) entry in its forwarding table. The * means any IPv6 multicast source. The RP is
the root, while the DRs are the leaves, of the RPT.
The IPv6 multicast data addressed to the IPv6 multicast group G flows through the RP, reaches the
corresponding DR along the established RPT, and finally is delivered to the receiver.
When a receiver is no longer interested in the IPv6 multicast data addressed to a multicast group G, the
directly connected DR sends a prune message, which goes hop by hop along the RPT to the RP. Upon
receiving the prune message, the upstream node deletes the interface connected with this downstream
node from the outgoing interface list and checks whether it has receivers for that IPv6 multicast group.
If not, the router continues to forward the prune message to its upstream router.
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