Multicast routing and forwarding maintain a protocol routing table, multicast routing table, and multicast forwarding table. A multicast routing protocol creates multicast routing entries through RPF.
In the FW, multicast routing and forwarding consist of the following three aspects:
Each multicast routing protocol has its routing table, such as PIM routing table.
The multicast routing information of each multicast routing protocol forms a general multicast routing table.
The multicast routing table resides in the multicast route management module. It is composed of (S, G) entries. (S, G) indicates that S sends multicast data to G. If the multicast route management module supports multiple multicast protocols, the routing table contains multicast routes that are generated by the protocols. The routing entries are copied to the forwarding table.
The multicast forwarding table controls the forwarding of multicast data packets.
The multicast forwarding table guides the forwarding of multicast data packets. It remains consistent with the multicast routing table.
To ensure that multicast data is transmitted along the correct path, multicast routing protocols use the Reverse Path Forwarding (RPF) to create multicast routing entries.
The system performs RPF check based on the following types of routes:
Unicast routes
The unicast routing table collects the shortest paths to each destination.
Static multicast routes
The static multicast routing table provides RPF routing information that is specified through static configuration.