HP VPN Firewall Appliances Appendix Protocol Reference

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IPv6 PIM
Overview
IPv6 PIM provides IPv6 multicast forwarding by leveraging IPv6 unicast static routes or IPv6 unicast
routing tables generated by any IPv6 unicast routing protocol, such as RIPng, OSPFv3, IS-ISv6, or BGP4+.
IPv6 PIM uses an IPv6 unicast routing table to perform RPF check to implement IPv6 multicast forwarding.
Independent of the IPv6 unicast routing protocols running on the device, IPv6 multicast routing can be
implemented as long as the corresponding IPv6 multicast routing entries are created through IPv6 unicast
routes. IPv6 PIM uses the RPF mechanism to implement IPv6 multicast forwarding. When an IPv6
multicast packet arrives on an interface of the device, RPF check is performed on it. If the RPF check
succeeds, the device creates the corresponding routing entry and forwards the packet. If the RPF check
fails, the device discards the packet. For more information about RPF, see "RPF check mechanism"
Ba
sed on the implementa
tion mechanism, IPv6 PIM supports the following modes:
• Protocol Independent Multicast–Dense Mode for IPv6 (IPv6 PIM-DM)
• Protocol Independent Multicast–Sparse Mode for IPv6 (IPv6 PIM-SM)
• Protocol Independent Multicast Source-Specific Multicast for IPv6 (IPv6 PIM-SSM)
In this document, a network comprising IPv6 PIM routers is referred to as an "IPv6 PIM domain."
The term "router" in this document refers to both routers and routing-capable firewalls.
IPv6 PIM-DM overview
IPv6 PIM-DM is a type of dense mode IPv6 multicast protocols. It uses the push mode for IPv6 multicast
forwarding, and is suitable for small-sized networks with densely distributed IPv6 multicast members.
The following describes the basic implementation of IPv6 PIM-DM:
• IPv6 PIM-DM assumes that at least one IPv6 multicast group member exists on each subnet of a
network, so IPv6 multicast data is flooded to all nodes on the network. Then, branches without IPv6
multicast forwarding are pruned from the forwarding tree, leaving only those branches that contain
receivers. This flood-and-prune process takes place periodically. Pruned branches resume IPv6
multicast forwarding when the pruned state times out. Data is flooded again down these branches,
and then the branches are pruned again.
• When a new receiver on a previously pruned branch joins an IPv6 multicast group, to reduce the
join latency, IPv6 PIM-DM uses the graft mechanism to resume IPv6 multicast data forwarding to
that branch.
In general, the IPv6 multicast forwarding path is a source tree. That is, it is a forwarding tree with the IPv6
multicast source as its "root" and IPv6 multicast group members as its "leaves." Because the source tree
is the shortest path from the IPv6 multicast source to the receivers, it is also called SPT.
The working mechanism of IPv6 PIM-DM is summarized as follows:
• Neighbor discovery
• SPT establishment
• Graft