Operation Manual – MulticastH3C S5600 Series Ethernet Switches Chapter 1 Multicast Overview1-11I. Layer 3 multicast protocolsLayer 3 multicast protocols include multicast group management protocols andmulticast routing protocols. Figure 1-5 describes where these multicast protocols are ina network.AS 1 AS 2SourceReceiver ReceiverReceiverPIM PIMMSDPIGMP IGMPIGMPFigure 1-5 Positions of Layer 3 multicast protocols1) Multicast management protocolsTypically, the Internet Group Management Protocol (IGMP) is used between hosts andLayer 3 multicast devices directly connected with the hosts. These protocols define themechanism of establishing and maintaining group memberships between hosts andLayer 3 multicast devices.2) Multicast routing protocolsA multicast routing protocol runs on Layer 3 multicast devices to establish and maintainmulticast routes and forward multicast packets correctly and efficiently. Multicast routesconstitute a loop-free data transmission path from a data source to multiple receivers,namely a multicast distribution tree.In the ASM model, multicast routes come in intra-domain routes and inter-domainroutes.z An intra-domain multicast routing protocol is used to discover multicast sourcesand build multicast distribution trees within an autonomous system (AS) so as todeliver multicast data to receivers. Among a variety of mature intra-domainmulticast routing protocols, Protocol Independent Multicast (PIM) is a popular one.Based on the forwarding mechanism, PIM comes in two modes – dense mode(often referred to as PIM-DM) and sparse mode (often referred to as PIM-SM).
