H3C Technologies H3C S7500E Series Switches - Manual (Page 357)

13-6
z When a receiver is interested in the IPv6 multicast data addressed to a specific IPv6
multicast group, the router connected to this receiver sends a join message to the RP
corresponding to that IPv6 multicast group. The path along which the message goes hop by
hop to the RP forms a branch of the RPT.
z When an IPv6 multicast source sends IPv6 multicast streams to an IPv6 multicast group,
the source-side designated router (DR) first registers the multicast source with the RP by
sending register messages to the RP by unicast until it receives a register-stop message
from the RP. The arrival a register message at the RP triggers the establishment of an SPT.
Then, the IPv6 multicast source sends subsequent IPv6 multicast packets along the SPT to
the RP. Upon reaching the RP, the IPv6 multicast packet is duplicated and delivered to the
receivers along the RPT.
IPv6 multicast traffic is duplicated only where the distribution tree branches, and this process
automatically repeats until the IPv6 multicast traffic reaches the receivers.
How IPv6 PIM-SM Works
The working mechanism of IPv6 PIM-SM is summarized as follows:
z Neighbor discovery
z DR election
z RP discovery
z Embedded RP
z RPT establishment
z IPv6 Multicast source registration
z Switchover to SPT
z Assert
Neighbor discovery
IPv6 PIM-SM uses the similar neighbor discovery mechanism as IPv6 PIM-DM does. Refer to
Neighbor 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.