3Com CoreBuilder 3500, Implementation Manual, Page: 334 / 592

334 C
HAPTER
13: IP M
ULTICAST
R
OUTING
How a Network
Supports IP
Multicast
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 Routing 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
IP multicast application sources
L3
L3
L3
Router-to-router
communication
Router-to-host
communication
Router-to-host
communication