Ipv6 Pim-Sm Overview - HP 6125XLG Ip Multicast Configuration Manual

IPv6 PIM-SM overview

IPv6 PIM-DM uses the flood-and-prune cycles to build SPTs for IPv6 multicast data forwarding. Although
an SPT has the shortest paths from the IPv6 multicast source to the receivers, it is built with a low efficiency.
IPv6 PIM-DM is not suitable for large- and medium-sized networks.
IPv6 PIM-SM uses the pull mode for IPv6 multicast forwarding, and it is suitable for large-sized and
medium-sized networks with sparsely and widely distributed IPv6 multicast group members.
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 multicast receiver 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 the source-side DR receives IPv6 multicast data from an IPv6 multicast source, it must register
the source with the RP by unicasting register messages to the RP. The IPv6 multicast source 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 the same 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
discovery."
MLD."
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