362
Configuring IPv6 multicast routing and
forwarding
This chapter describes IPv6 multicast routing and forwarding, how to configure IPv6 multicast routing
and forwarding, configuration examples, and troubleshooting methods.
Overview
In IPv6 multicast implementations, the following types of tables implement multicast routing and
forwarding:
•
Multicast routing table of an IPv6 multicast routing protocol
—Each IPv6 multicast routing
protocol has its own multicast routing table, such as the IPv6 PIM routing table.
•
General IPv6 multicast routing table
—The multicast routing information of different IPv6
multicast routing protocols forms a general IPv6 multicast routing table.
•
IPv6 multicast forwarding table
—The IPv6 multicast forwarding table guides the forwarding
of IPv6 multicast packets.
An IPv6 multicast forwarding table consists of a set of (S, G) entries. Each entry contains the routing
information for delivering multicast data from a multicast source to a multicast group. If a router
supports multiple IPv6 multicast protocols, its IPv6 multicast routing table contains all routes that
these protocols have generated. The router chooses the optimal route from the IPv6 multicast
routing table based on the configured multicast routing and forwarding policy and installs the route
entry into its IPv6 multicast forwarding table.
The term "interface" in this chapter collectively refers to Layer 3 interfaces, including VLAN
interfaces and Layer 3 Ethernet interfaces. You can set an Ethernet port as a Layer 3 interface by
using the
port link-mode route
command (see
Layer 2—LAN Switching Configuration Guide
).
RPF check mechanism
An IPv6 multicast routing protocol relies on the existing IPv6 unicast routing information or IPv6
MBGP routes in creating IPv6 multicast routing entries. When creating IPv6 multicast routing table
entries, an IPv6 multicast routing protocol uses the RPF check mechanism to ensure IPv6 multicast
data delivery along the correct path. The RPF check mechanism also helps avoid data loops caused
by various reasons.
RPF check process
A multicast routing protocol uses the following tables to perform the RPF check:
•
IPv6 unicast routing table
—Contains unicast routing information.
•
IPv6 MBGP routing table
—Contains IPv6 MBGP multicast routing information.
When performing an RPF check, a router searches its IPv6 unicast routing table and IPv6 MBGP
routing table at the same time. The specific process is as follows:
1.
The router chooses an optimal route from the IPv6 unicast routing table and the IPv6 MBGP
routing table, respectively.
{
The router searches its IPv6 unicast routing table and automatically selects an optimal route
to the packet source address. The outgoing interface of the route is the RPF interface and
the next hop is the RPF neighbor. The router considers the path of the IPv6 multicast packet
that the RPF interface receives from the RPF neighbor as the shortest path that leads back
to the source.
