R211x-HP Flexfabric 11900 IP Multicast Configuration Guide

Configuring multicast routing and forwarding

Overview

The following tables are involved in multicast routing and forwarding:

• Multicast routing table of each multicast routing protocol, such as the PIM routing table.

• General multicast routing table that summarizes multicast routing information generated by different

multicast routing protocols. The multicast routing information from multicast sources to multicast

groups are stored in a set of (S, G) routing entries.

• Multicast forwarding table that guides multicast forwarding. The optimal routing entries in the

multicast routing table are added to the 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 creates multicast routing entries based on the existing unicast routes or static

multicast routes. During the process, the reverse path forwarding (RPF) check mechanism ensures the

multicast data delivery along the correct paths and avoids data loops.

A multicast routing protocol uses the following tables to perform an RPF check:

• Unicast routing table—Contains unicast routing information.

• Static multicast routing table—Contains RPF routes that are manually configured.

Static multicast routing table is used for RPF check rather than multicast routing.

RPF check process

When performing an RPF check, the router searches its unicast routing table and static multicast routing

table at the same time using the following process:

1. The router separately chooses an optimal route from the unicast routing table and the static

multicast routing table:

{ The router looks up its unicast routing table by using the IP address of the packet source as the

destination address, and automatically chooses an optimal unicast route. 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 packet that the RPF interface receives from the RPF neighbor as the

shortest path that leads back to the source.

{ The router looks up its static multicast routing table by using the IP address of the packet source

as the source address, and automatically chooses an optimal static multicast route. The route

explicitly defines the RPF interface and the RPF neighbor.

2. The router selects one of the two optimal routes as the RPF route according to the following

principles:

{ If the router uses the longest prefix match principle, the router selects the matching route as the

RPF route. If the routes have the same mask, the router selects the route that has the highest