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MULTICAST ROUTING AND
FORWARDING CONFIGURATION
When configuring multicast routing and forwarding, go to these sections for
information you are interested in:
■ “Multicast Routing and Forwarding Overview” on page 701
■ “Configuring Multicast Routing and Forwarding” on page 706
■ “Displaying and Maintaining Multicast Routing and Forwarding” on page 709
■ “Configuration Examples” on page 709
■ “Troubleshooting Multicast Routing and Forwarding” on page 713
n
The term “router” in this document refers to a router in a generic sense or a Layer
3 switch running an IP routing protocol.
Multicast Routing and
Forwarding Overview
Introduction to Multicast
Routing and Forwarding
In multicast implementations, multicast routing and forwarding are implemented
by three types of tables:
■ Each multicast routing protocol has its own multicast routing table, such as PIM
routing table.
■ The information of different multicast routing protocols forms a general
multicast routing table.
■ The multicast forwarding table is directly used to control the forwarding of
multicast packets.
A multicast forwarding table consists of a set of (S, G) entries, each indicating 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 will include 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 installs the route entry
into its multicast forwarding table.
RPF Mechanism When creating multicast routing table entries, a multicast routing protocol uses
the reverse path forwarding (RPF) mechanism to ensure multicast data delivery
along the correct path.
The RPF mechanism enables routers to correctly forward multicast packets based
on the multicast route configuration. In addition, the RPF mechanism also helps
avoid data loops caused by various reasons.
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