3Com S7906E Configuration Manual page 1285

RP discovery
Embedded RP
RPT establishment
IPv6 Multicast source registration
Switchover to SPT
Assert
Neighbor discovery
IPv6 PIM-SM uses the similar neighbor discovery mechanism as IPv6 PIM-DM does. Refer to
discovery.
DR election
IPv6 PIM-SM also uses hello messages to elect a DR for a multi-access network (such as a LAN). The
elected DR will be the only IPv6 multicast forwarder on this multi-access network.
In the case of a multi-access network, a DR must be elected, no matter this network connects to IPv6
multicast sources or to receivers. The DR at the receiver side sends join messages to the RP; the DR at
the IPv6 multicast source side sends register messages to the RP.
A DR is elected on a multi-access subnet by means of comparison of the priorities and IPv6
link-local addresses carried in hello messages.
MLD must be enabled on a device that acts as a receiver-side DR before receivers attached to this
device can join IPv6 multicast groups through this DR.
For details about MLD, refer to MLD Configuration in the IP Multicast Volume.
Figure 1-3 DR election
DR
Source
Hello message
Register message
Join message
As shown in Figure 1-3, the DR election process is as follows:
DR
RP
1-6
Receiver
Receiver
Neighbor