Multicast Protocols - 3Com 4500 Configuration Manual

Multicast Protocols

Generally, we refer to IP multicast working at the network layer as Layer 3 multicast and the
corresponding multicast protocols as Layer 3 multicast protocols, which include IGMP, PIM, and
MSDP; we refer to IP multicast working at the data link layer as Layer 2 multicast and the
corresponding multicast protocols as Layer 2 multicast protocols, which include IGMP Snooping.
This section provides only general descriptions about applications and functions of the Layer 2 and
Layer 3 multicast protocols in a network. For details about these protocols, refer to the related
chapters of this manual.
Layer 3 multicast protocols
Layer 3 multicast protocols include multicast group management protocols and multicast routing
protocols. Figure 1-5
Figure 1-5 Positions of Layer 3 multicast protocols
Receiver
1) Multicast management protocols
Typically, the Internet Group Management Protocol (IGMP) is used between hosts and Layer 3
multicast devices directly connected with the hosts. These protocols define the mechanism of
establishing and maintaining group memberships between hosts and Layer 3 multicast devices.
2) 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 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-domain routes.
An intra-domain multicast routing protocol is used to discover multicast sources and build multicast
distribution trees within an autonomous system (AS) so as to deliver multicast data to receivers.
describes where these multicast protocols are in a network.
AS 1
IGMP
PIM
Source
Receiver
MSDP
Receiver
1-9
AS 2
IGMP
PIM
IGMP