HP A8800 Configuration Manual page 396

1. Router B and Router C multicast DF election messages to all PIM routers (224.0.0.13). The election
messages carry the RP's address, and the priority and metric of the unicast route, MBGP route, or
multicast static route to the RP.
2. The router with a route of the highest priority becomes the DF.
3. In the case of a tie, the router with the route with the lowest metric wins the DF election.
4. In the case of a tie in the metric, the router with the highest link-local IPv6 address wins.
Bidirectional RPT building
A bidirectional RPT comprises two parts: receiver-side RPT and source-side RPT. The receiver-side RPT is
rooted at the RP and takes the routers directly connected with the receivers as leaves. The source-side RPT
is also rooted at the RP but takes the routers directly connected with the IPv6 multicast sources as leaves.
The processes for building these two parts are different.
Figure 109 RPT building at the receiver side
Receiver
Host A
Source
Server A
As shown in
in IPv6 PIM-SM:
1. When a receiver joins IPv6 multicast group G, it uses an MLD message to inform the directly
connected router.
2. Upon getting the receiver information, the router sends a join message, which is forwarded hop by
hop to the RP of the IPv6 multicast group.
3. The routers along the path from the receiver's directly connected router to the RP form an RPT
branch, and each router on this branch adds a (*, G) entry to its forwarding table. The * means
any IPv6 multicast source.
When a receiver is no longer interested in the multicast data addressed to IPv6 multicast group G, the
directly connected router sends a prune message, which goes hop by hop along the reverse direction of
the RPT to the RP. Upon receiving the prune message, each upstream node deletes the interface
connected with the downstream node from the outgoing interface list and checks whether it has receivers
in that IPv6 multicast group. If not, the router continues to forward the prune message to its upstream
router.
Join message
Receiver-side RPT
IPv6 Multicast packets
Figure 109, the process for building a receiver-side RPT is similar to that for building an RPT
RP
384
Source
Server B
Receiver
Host B
Receiver
Host C