3
USING MULTICAST FILTERING
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.