3Com WX3000 Layer 2 multicast protocols, 5Positions of Layer 3 multicast protocols

Figure 1-5Positions of Layer 3 multicast protocols

Receiver AS 1 Receiver AS 2

IGMP

IGMP

PIM	PIM
	MSDP

IGMP

Source 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.

z

z

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. Among a variety of mature intra-domain multicast 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).

An inter-domain multicast routing protocol is used for delivery of multicast information between two ASs. So far, mature solutions include multicast source discovery protocol (MSDP).

For the SSM model, multicast routes are not divided into inter-domain routes and intra-domain routes. Since receivers know the position of the multicast source, channels established through PIM-SM are sufficient for multicast information transport.

Layer 2 multicast protocols

Layer 2 multicast protocols include IGMP Snooping and multicast VLAN. Figure 1-6 shows where these protocols are in the network.

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