3Com 3C17203 - SuperStack 3 Switch 4400, Implementation Manual

Page: 39 / 153

3
U
SING
M
ULTICAST
F
ILTERING
Multicast filtering improves the performance of networks that carry
multicast traffic.
This chapter explains multicasts, multicast filtering, and how multicast
filtering can be implemented on your Switch. It covers the following
topics:
■
What is an IP Multicast?
■
Multicast Filtering
■
IGMP Multicast Filtering
For detailed descriptions of the Web interface operations and the
Command Line Interface (CLI) commands that you require to manage the
Switch please refer to the Management Interface Reference Guide
supplied in HTML format on the CD-ROM that accompanies your Switch.
What is an IP
Multicast?
A multicast is a packet that is intended for “one-to-many” and “many-
to-many” communication. Users explicitly request to participate in the
communication by joining an endstation to a specific multicast group. If
the network is set up correctly, a multicast can only be sent to an
endstation or a subset of endstations in a LAN, or VLAN, that belong to
the relevant multicast group.
Multicast group members can be distributed across multiple
subnetworks; thus, multicast transmissions can occur within a campus
LAN or over a WAN. In addition, networks that support IP multicast send
only
one copy of the desired information across the network until the
delivery path that reaches group members diverges. It is only at these
points that multicast packets are replicated and forwarded, which makes
efficient use of network bandwidth.