Operation Manual – Multicast ProtocolH3C S3610&S5510 Series Ethernet Switches Chapter 8 Multicast Policy Configuration8-1Chapter 8 Multicast Policy Configuration8.1 Multicast Policy OverviewTo ensure the correct transmission of multicast packets in the network, every multicastpacket is subject to a reverse path forwarding (RPF) check on the incoming interface:z If the packet passes the RPF check, the router creates the correspondingmulticast forwarding entry and forwards the packet;z If the packet fails the RPF check, it is discarded.Multicast policies are policies used for filtering the RPF routing information.8.1.1 Introduction to Multicast PolicyI. Multicast routing and forwardingIn multicast implementations, multicast routing and forwarding include three aspects:z Each multicast routing protocol has its own multicast routing table, such as PIMrouting table.z The information of different multicast routing protocols forms a general multicastrouting table.z The multicast forwarding table is directly used to control the forwarding of multicastpackets.The multicast forwarding table consists of a group of (S, G) entries, each indicating aroute from a multicast source to a multicast group. If a router supports multiple multicastprotocols, its multicast routing table will include routes generated by multiple protocols.The router chooses the optimal route from the multicast routing table based on theconfigured multicast routing and forwarding policy and updates its multicast forwardingtable accordingly.The multicast forwarding table is the table that guides multicast forwarding. Uponreceiving a multicast packet that a multicast source S sends to a multicast group G, thedevice first searches its multicast forwarding table:z If the corresponding (S, G) entry exists, and the interface on which the packet hasactually arrived is the incoming interface in the multicast forwarding table, therouter forwards the packet to all the outgoing interfaces.z If the corresponding (S, G) entry exists, but the interface on which the packet hasactually arrived is not the incoming interface in the multicast forwarding table, therouter performs an RPF check for the packet. If the packet passes the RPF check,the router modifies the incoming interface to the interface on which the packet hasactually arrived and forwards the packet to all the outgoing interfaces; if the RFPcheck fails, the router discards the packet.
