1-11Multicast 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/MLD,PIM/IPv6 PIM, MSDP, and MBGP/IPv6 MBGP; we refer to IP multicast working at the data linklayer as Layer 2 multicast and the corresponding multicast protocols as Layer 2 multicast protocols,which include IGMP Snooping/MLD Snooping, and multicast VLAN/IPv6 multicast VLAN.z IGMP Snooping, IGMP, multicast VLAN, PIM, MSDP, and MBGP are for IPv4, MLD Snooping,MLD, IPv6 multicast VLAN, IPv6 PIM, and IPv6 MBGP are for IPv6.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 1-8 describes where these multicast protocols are in a network.Figure 1-8 Positions of Layer 3 multicast protocols1) Multicast management protocolsTypically, the internet group management protocol (IGMP) or multicast listener discovery protocol (MLD)is used between hosts and Layer 3 multicast devices directly connected with the hosts. These protocolsdefine the mechanism of establishing and maintaining group memberships between hosts and Layer 3multicast 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.
