A multicast forwarding table consists of groups of (S, G) entries. In an (S, G) entry, S indicates the source information, and G indicates the group information. The multicast route management module supports multiple multicast routing protocols. The multicast forwarding table therefore collects multicast routing entries generated by various types of protocols.
RPF check
This function is used to find an optimal unicast route to the multicast source and build a multicast distribution tree. The outbound interface of the unicast route functions as the inbound interface of the forwarding entry. Then, when the forwarding module receives a multicast data packet, the module matches the packet with the forwarding entry and checks whether the inbound interface of the packet is correct. If the inbound interface of the packet is identical with the outbound interface of the unicast routing entry, the packet passes the RPF check; otherwise, the packet fails the RPF check and is discarded. The RPF check prevents traffic loops in multicast data forwarding.
Multicast load splitting
If a multicast load splitting policy is configured, different forwarding entries that specify the same multicast source can select different equal-cost routes as RPF routes to guide multicast data forwarding. The RPF routes of forwarding entries can be hashed to different equal-cost routes, and multicast data distribution is then implemented.
Longest-match multicast routing
During multicast routing, the router preferentially selects the route with the longest matched mask length to implement accurate route matching.
Multicast multi-topology
The multicast multi-topology function helps you plan a multicast topology for multicast services on a physical network. Then, when a multicast device performs the RPF check, the device searches for routes and builds a multicast distribution tree only in the multicast topology. In this manner, the problem that multicast services heavily depend on unicast routes is addressed.
Multicast Boundary
Multicast boundaries are used to control multicast information transmission by allowing the multicast information of each multicast group to be transmitted only within a designated scope. A multicast boundary can be configured on an interface to form a closed multicast forwarding area. After a multicast boundary is configured for a specific multicast group on an interface, the interface cannot receive or send multicast packets for the multicast group.