1-9Multicast Protocolsz Generally, we refer to IP multicast working at the network layer as Layer 3 multicast and thecorresponding multicast protocols as Layer 3 multicast protocols, which include IGMP, PIM, MSDP,and MBGP; we refer to IP multicast working at the data link layer as Layer 2 multicast and thecorresponding multicast protocols as Layer 2 multicast protocols, which include IGMP Snooping,and multicast VLAN.z This section provides only general descriptions about applications and functions of the Layer 2 andLayer 3 multicast protocols in a network..Layer 3 multicast protocolsLayer 3 multicast protocols include multicast group management protocols and multicast routingprotocols. Figure 1-5 describes where these multicast protocols are in a network.Figure 1-5 Positions of Layer 3 multicast protocolsAS 1 AS 2SourceReceiver ReceiverReceiverPIM PIMMSDP/MBGPIGMP IGMPIGMP1) Multicast management protocolsTypically, the internet group management protocol (IGMP) is used between hosts and Layer 3 multicastdevices directly connected with the hosts. These protocols define the mechanism of establishing andmaintaining group memberships between hosts and Layer 3 multicast devices.2) Multicast routing protocolsA multicast routing protocol runs on Layer 3 multicast devices to establish and maintain multicast routesand forward multicast packets correctly and efficiently. Multicast routes constitute a loop-free datatransmission 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-domain routes.z An intra-domain multicast routing protocol is used to discover multicast sources and build multicastdistribution trees within an AS so as to deliver multicast data to receivers. Among a variety of
