3Com Switch 8800 Advanced Software V5 Configuration Guide

MULTICAST ROUTING AND

FORWARDING CONFIGURATION

When configuring multicast routing and forwarding, go to the following sections

for information you are interested in:

■ “Multicast Routing and Forwarding Overview” on page 503

■ “Configuring Multicast Routing and Forwarding” on page 507

■ “Displaying and Maintaining Multicast Routing and Forwarding” on page 510

■ “Configuration Examples” on page 511

■ “Troubleshooting Multicast Routing and Forwarding” on page 513

The term "router" in this document refers to a router in a generic sense or a

Switch 8800 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 device supports multiple multicast protocols, its multicast

routing table will include routes generated by multiple protocols. The device

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 devices 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.