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Configuring multicast routing and
forwarding
This chapter describes multicast routing and forwarding, how to configure multicast routing and
forwarding, configuration examples, and troubleshooting methods.
Hardware compatibility
To use GRE related features on the switches, you must install SD or EB cards.
Overview
In multicast implementations, the following types of tables implement multicast routing and
forwarding:
•
Multicast routing table of a multicast routing protocol
—Each multicast routing protocol has
its own multicast routing table, such as the PIM routing table.
•
General multicast routing table
—The multicast routing information of different multicast
routing protocols forms a general multicast routing table.
•
Multicast forwarding table
—The multicast forwarding table helps guide the forwarding of
multicast packets.
A multicast routing 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 multicast protocols, its multicast routing table contains all routes generated by
multiple protocols. The router chooses the optimal route from the multicast routing table based on
the configured multicast routing and forwarding policy and adds the route entry to its 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
A multicast routing protocol relies on the existing unicast routes, MBGP routes, or static multicast
routes in creating multicast routing entries. When creating multicast routing table entries, a multicast
routing protocol uses the RPF check mechanism to ensure multicast data delivery along the correct
paths.
In addition, the RPF check mechanism also helps avoid data loops.
RPF check process
A multicast routing protocol uses the following tables to perform the RPF check:
•
Unicast routing table
—Contains unicast routing information.
•
MBGP
multicast
routing table
—Contains MBGP multicast routing information.
•
Static multicast routing table
—Contains static multicast routes.
MBGP multicast routing table and static multicast routing table are
used for RPF check rather than
multicast routing.
When a router performs an RPF check, it looks up its unicast routing table, MBGP routing table, and
static multicast routing table.
