How A Network Supports Ip Multicast; Ip Multicast Routing - 3Com corebuilder 3500 Implementation Manual

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How a Network

To support IP multicast, the sending and receiving nodes, as well as the

network infrastructure between them, must be multicast-enabled.

Specifically, there must be cohesive support for IP multicast in the

following components: TCP/IP protocol stack, operating systems,

application software, NICs, and Layer 3 devices. Support for IP multicast

in Layer 2 devices is not required by the standard, but is desirable, as

explained later in this section.

IP multicast transmissions fundamentally depend on multicast-enabled

Layer 3 devices (traditional routers or Layer 3 switches; hereafter both are

called routers) to direct packets on an efficient path from sources to

destinations.

As shown in Figure 66, routers that support IP multicast must accomplish

two important tasks:

Communicate with other routers to determine the shortest, loopfree

delivery path between an IP multicast source and its group members

Communicate with hosts on its directly attached subnetworks to

determine which hosts want to join or leave IP multicast groups

Figure 66 IP Multicast Communication Processes

Router-to-host

communication

IP multicast application sources

Router-to-router

communication

Router-to-host

communication