Configuring Multicast Routing And Forwarding; Overview; Rpf Check Mechanism - HP 5920 series Configuration Manual

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.
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General multicast routing table that summarizes multicast routing information of different multicast
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routing protocols.
Multicast forwarding table that guides multicast forwarding.
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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 routing protocols, its multicast routing table lists all routes generated by these protocols. The
router chooses an optimal route from the multicast routing table based on the configured multicast routing
and forwarding policy, and adds this route entry to its multicast forwarding table.

RPF check mechanism

A multicast routing protocol uses Reverse path forwarding (RPF) check to ensure the multicast data
delivery along the correct paths when the multicast routing protocol creates multicast routing entries
based on the existing unicast routes or static multicast routes. RPF check also helps avoid data loops.
A multicast routing protocol uses the following tables to perform an RPF check:
Unicast routing table—Contains unicast routing information.
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• 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:
The router separately chooses an optimal route from the unicast routing table and the static
1.
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.
The router selects one of the two optimal routes as the RPF route according to the following
2.
principles:
If the router uses the longest prefix match principle, it selects the matching route as the RPF route.
If the routes have the same mask, the router selects the route that has the highest priority as the
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