Operation Manual – MulticastH3C S7500 Series Ethernet Switches Chapter 1 Multicast Overview1-9AS 1 AS 2SourceReceiver ReceiverReceiverPIM PIMMSDPIGMP IGMPIGMPsFigure 1-5 Positions of multicast-relevant protocolI. Multicast group management protocolInternet group management protocol (IGMP) runs between hosts and multicast routers.This protocol defines the mechanism of establishing and maintaining groupmembership between hosts and routers.II. Multicast routing protocolsA multicast routing protocol operates between multicast routers to establish andmaintain multicast routes and forward multicast packets accurately and effectively. Amulticast route establishes a loop-free data transmission path from a data source tomultiple receivers. The multicast routing protocol is designed to establish a distributiontree. Multicast routers can establish the data transmission path (namely, distributiontree) in many ways.Like unicast routes, multicast routes come in intra-domain routes and inter-domainroutes. Intra-domain multicast routes are quite mature now. Protocol independentmulticast (PIM) is the most commonly used protocol currently. It can cooperate with anyunicast routing protocol.1.3 Forwarding Mechanism of Multicast PacketsIn a multicast model, a multicast source transmits information to the multicast group,which is identified by the multicast group address in the destination address field of anIP data packet. Unlike a unicast model, a multicast model must forward data packets tomultiple external interfaces so that all receivers can receive the packets. Therefore theforwarding process of multicast is more complicated than unicast.
