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Configuring IPv6 PIM
Overview
IPv6 Protocol Independent Multicast (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, IPv6 IS-IS, or IPv6 BGP. IPv6 PIM uses the underlying IPv6
unicast routing to generate an IPv6 multicast routing table without relying on any particular IPv6
unicast routing protocol.
IPv6 PIM uses the RPF mechanism to implement multicast forwarding. When an IPv6 multicast
packet arrives on an interface of the device, the packet undergoes an RPF check. If the RPF check
succeeds, the device creates an IPv6 multicast routing entry and forwards the packet. If the RPF
check fails, the device discards the packet. For more information about RPF, see "Configuring IPv6
multicast routing and forwarding."
Based on the implementation mechanism, IPv6 PIM includes the following categories:
•
IPv6 Protocol Independent Multicast–Dense Mode (IPv6 PIM-DM)
•
IPv6 Protocol Independent Multicast–Sparse Mode (IPv6 PIM-SM)
•
IPv6 Bidirectional Protocol Independent Multicast (IPv6 BIDIR-PIM)
•
IPv6 Protocol Independent Multicast Source-Specific Multicast (IPv6 PIM-SSM)
In this document, an IPv6 PIM domain refers to a network composed of IPv6 PIM routers.
IPv6 PIM-DM overview
IPv6 PIM-DM uses the push mode for multicast forwarding and is suitable for small networks with
densely distributed IPv6 multicast members.
IPv6 PIM-DM assumes that all downstream nodes want to receive IPv6 multicast data from a source,
so IPv6 multicast data is flooded to all downstream nodes on the network. Branches without
downstream receivers are pruned from the forwarding trees, leaving only those branches that
contain receivers. When the pruned branch has new receivers, the graft mechanism turns the
pruned branch into a forwarding branch.
In IPv6 PIM-DM, the multicast forwarding paths for an IPv6 multicast group constitute a forwarding
tree. The forwarding tree is rooted at the IPv6 multicast source and has multicast group members as
its "leaves." Because the forwarding tree consists of the shortest paths from the IPv6 multicast
source to the receivers, it is also called a "shortest path tree (SPT)."
Neighbor discovery
In an IPv6 PIM domain, each IPv6 PIM interface periodically multicasts IPv6 PIM hello messages to
all other IPv6 PIM routers on the local subnet. Through the exchanging of hello messages, all IPv6
PIM routers determine their IPv6 PIM neighbors, maintain IPv6 PIM neighboring relationship with
other routers, and build and maintain SPTs.
SPT building
The process of building an SPT is the flood-and-prune process:
1.
In an IPv6 PIM-DM domain, the IPv6 multicast data from the IPv6 multicast source S to the IPv6
multicast group G is flooded throughout the domain. A router performs an RPF check on the
IPv6 multicast data. If the check succeeds, the router creates an (S, G) entry and forwards the
data to all downstream nodes in the network. In the flooding process, all the routers in the IPv6
PIM-DM domain create the (S, G) entry.
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Troubleshooting
