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Page 9 | AlliedWare™ OS How To Note: IGMP
IGMP snooping > Example
IGMP snooping
In this example, we discuss IGMP snooping, the key to efficient multicast traffic flow in a
layer 2 network. IGMP snooping is enabled by default on switch ports in Allied Telesis
managed layer 3 switches and routers—it does not require any configuration.
In a single-switch network, IGMP snooping makes multicasting happen with no configuration
at all. All you need to do is connect your server and clients to the switch.
In a multi-switch network, at least one switch must also have an IGMP configuration. This
switch is called the IGMP Querier and coordinates the flow of multicast information through
the network. The following example describes a multi-switch configuration, so as well as
discussing the effect of IGMP snooping, it outlines the actions that the Querier takes.
"Multiple potential IGMP queriers" on page 15 discusses the role of the Querier in greater
detail.
Example
This example has a 3-switch loop, as shown in the following figure. One of the switches is
running IGMP and the other two switches are running IGMP snooping.
Multicast Server
AT-8948
Switch 1:
Querier
Rapier 24i
Switch 2:
Snooper
Client 1
Rapier 24i
Switch 3:
Snooper
Client 2
port 1
port 2 port 3
port 25 port 25
port 26port 26
port 50
(blocked by STP)
port 49
igmp-snooper.eps