Allied Telesis AR400 - Manual (Page 15)

Page 15 | AlliedWare™ OS How To Note: IGMP
Multiple potential IGMP queriers > Example
Multiple potential IGMP queriers
To find out more about IGMP, we next investigate what happens when more than one router
or switch has an IGMP configuration.
RFC 2236, Internet Group Management Protocol, Version 2, says that each Layer 2 network
should have only one IGMP Querier. You may configure IGMP on more than router or
switch, perhaps for redundancy, but the routers and switches have a pseudo election and the
device with the lower IP becomes the operating IGMP Querier. This example describes a
network with two potential Queriers.
Example
The network for this example uses the same loop as for "IGMP snooping" on page 9 and is
shown in the following figure.
Both switch 1 and switch 2 are configured with IGMP, making both of them potential
Queriers. Switch 3, by default configuration, is an IGMP Snooper.
Multicast Server
AT-8948
Switch 1:
Potential Querier
Rapier 24i
Switch 2:
Elected Querier
Client 1
Rapier 24i
Switch 3:
Snooper
Client 2
port 1
port 2 port 3
port 25 port 25
port 26 port 26
port 50
(blocked by STP)
port 49
igmp-querier.eps