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Chapter 3 General Management of the Switch 3-55
The purpose of IP multicast filtering is to optimize a switched network’s
performance, so that multicast packets will only be forwarded to those ports
containing multicast group hosts or multicast routers/switches, instead of flooding
traffic to all ports in the subnet (VLAN).
3.3.2.1 Configuring IGMP Snooping Parameters
You can configure the switch to forward multicast traffic intelligently. Based on the
IGMP query and report messages, the switch forwards traffic only to the ports that
request multicast traffic. This prevents the switch from broadcasting the traffic to all
ports and possibly disrupting network performance.
Note the following points about IGMP snooping:
■ IGMP Snooping – The switch can passively snoop on IGMP Query and Report
packets transferred between IP multicast routers/switches and IP multicast host
groups to identify the IP multicast group members. It monitors the IGMP packets
passing through it, picks out the group registration information, and configures
multicast filters accordingly.
■ IGMP Querier – A router, or multicast-enabled switch, can periodically ask their
hosts if they want to receive multicast traffic. If there is more than one router/
switch on the LAN performing IP multicasting, one of these devices is elected
“querier” and assumes the role of querying the LAN for group members. It then
propagates the service requests on to any upstream multicast switch/router to
ensure that it will continue to receive the multicast service.
Note – Multicast routers use this information, along with a multicast routing
protocol such as DVMRP, to support IP multicasting across the Internet.
When configuring IGMP snooping through the web interface or CLI, the following
parameters are displayed or can be configured:
■ IGMP Snooping – The operating status of IGMP. When enabled, the switch will
monitor network traffic to determine which hosts want to receive multicast traffic.
The default is Disabled.
■ IGMP Protocol Version – The protocol version. Specify 1 or 2 for compatibility
with other devices on the network. The default is 2.
■ IGMP Querier – The operating status of IGMP querier. When enabled, the switch
can serve as the querier, which is responsible for asking hosts if they want to
receive multicast traffic. The default is Disabled.
■ Query Count – The maximum number of queries issued (between 2 and 10) for
which there has been no response before the querier takes action to drop a
client from the multicast group. The default is 2.