HP MSR2003 Configuration Manual page 288

The basic implementation of IPv6 PIM-SM is as follows:
• IPv6 PIM-SM assumes that no hosts need IPv6 multicast data. In the IPv6 PIM-SM mode, a host must
express its interest in the IPv6 multicast data for an IPv6 multicast group before the data is
forwarded to it. IPv6 PIM-SM implements multicast forwarding by building and maintaining
rendezvous point trees (RPTs). An RPT is rooted at a router that has been configured as the
rendezvous point (RP) for an IPv6 multicast group. The IPv6 multicast data to the group is forwarded
by the RP to the receivers along the RPT.
After a receiver host joins an IPv6 multicast group, the receiver-side designated router (DR) sends a
•
join message to the RP for the IPv6 multicast group. The path along which the message goes hop by
hop to the RP forms a branch of the RPT.
When IPv6 multicast data from an IPv6 multicast source to an IPv6 multicast group arrives, the
•
source-side DR must register the source with the RP for that group. The source-side DR encapsulates
the IPv6 multicast data within a register message and unicasts the register message to the RP. It
stops sending register message until it receives a register-stop message from the RP. When the RP
receives the register message, it triggers the establishment of an SPT. Then, the IPv6 multicast source
sends subsequent IPv6 multicast packets along the SPT to the RP. After reaching the RP, the multicast
packet is duplicated and delivered to the receivers along the RPT.
Multicast data is replicated wherever the RPT branches, and this process automatically repeats until the
IPv6 multicast data reaches the receivers.
Neighbor discovery
IPv6 PIM-SM uses a similar neighbor discovery mechanism as IPv6 PIM-DM does. For more information,
see "Neighbor
DR election
On a shared-media LAN like Ethernet, only a DR forwards IPv6 multicast data. A DR is required in both
the source-side network and receiver-side network. A source-side DR acts on behalf of the IPv6 multicast
source to send register messages to the RP. The receiver-side DR acts on behalf of the receiver hosts to
send join messages to the RP.
IMPORTANT:
MLD must be enabled on the device that acts as the receiver-side DR. Otherwise, the receiver hosts
attached to the DR cannot join any IPv6 multicast groups. For more information about MLD, see
"Configuring MLD."
discovery."
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