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Multicast protocols
Generally, Layer 3 multicast refers to IP multicast working at the network layer. The corresponding
multicast protocols are Layer 3 multicast protocols, which include IGMP, MLD, PIM, IPv6 PIM, MSDP,
MBGP, and IPv6 MBGP. Layer 2 multicast refers to IP multicast working at the data link layer. The
corresponding multicast protocols are Layer 2 multicast protocols, which include IGMP snooping, MLD
snooping, PIM snooping, IPv6 PIM snooping, multicast VLAN, and IPv6 multicast VLAN.
IGMP snooping, PIM snooping, multicast VLAN, IGMP, PIM, MSDP, and MBGP are for IPv4, and MLD
snooping, IPv6 PIM snooping, IPv6 multicast VLAN, MLD, IPv6 PIM, and IPv6 MBGP are for IPv6.
This section provides only general descriptions about applications and functions of the Layer 2 and Layer
3 multicast protocols in a network. For more information about these protocols, see the related chapters.
Layer 3 multicast protocols
Layer 3 multicast protocols include multicast group management protocols and multicast routing
protocols.
Figure 8 Positions of Layer 3 multicast protocols
• Multicast group management protocols
Typically, the Internet Group Management Protocol (IGMP) or Multicast Listener Discovery Protocol
(MLD) is used between hosts and Layer 3 multicast devices that directly connect to the hosts. These
protocols define the mechanism of establishing and maintaining group memberships between
hosts and Layer 3 multicast devices.
• Multicast routing protocols
A multicast routing protocol runs on Layer 3 multicast devices to establish and maintain multicast
routes and forward multicast packets correctly and efficiently. Multicast routes constitute loop-free
data transmission paths from a data source to multiple receivers, namely, a multicast distribution
tree.
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