Ipv6 Pim-Sm Overview - HP FlexNetwork 7500 Series Configuration Manual

Figure 94 Assert mechanism
As shown in
they both forward the packet to the local subnet. As a result, the downstream node Router C
receives two identical multicast packets. In addition, both Router A and Router B, on their
downstream interfaces, receive a duplicate packet forwarded by the other. After detecting this
condition, both routers send an assert message to all IPv6 PIM routers on the local subnet through
the interface that received the packet. The assert message contains the IPv6 multicast source
address (S), the IPv6 multicast group address (G), and the metric preference and metric of the IPv6
unicast route/MBGP route/static multicast route to the IPv6 multicast source. By comparing these
parameters, either Router A or Router B becomes the unique forwarder of the subsequent (S, G)
packets on the subnet. The comparison process is as follows:
The router with a higher metric preference to the IPv6 multicast source wins.
1.
If both routers have the same metric preference to the IPv6 multicast source, the router with a
2.
smaller metric to the IPv6 multicast source wins.
If both routers have the same metric, the router with a higher IPv6 link-local address on the
3.
downstream interface wins.

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. Therefore, 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.
IPv6 PIM-SM assumes that no hosts need IPv6 multicast data. A multicast receiver must express its
interest in the IPv6 multicast data for an IPv6 multicast group before the data is forwarded to it. A
rendezvous point (RP) is the core of an IPv6 PIM-SM domain. Relying on the RP, SPTs and
rendezvous point trees (RPTs) are established and maintained to implement IPv6 multicast data
forwarding. An SPT is rooted at the IPv6 multicast source and has the RPs as its leaves. An RPT is
rooted at the RP and has the receiver hosts as its leaves.
Neighbor discovery
IPv6 PIM-SM uses the same neighbor discovery mechanism as IPv6 PIM-DM does. For more
information, see
DR election
A designated router (DR) is required on 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.
Figure 94, after Router A and Router B receive an (S, G) packet from the upstream node,
"Neighbor discovery."
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