Allied Telesis AR400 manual Multiple potential IGMP queriers, Example

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.

	Multicast Server
	port 1	AT-8948
			Switch 1:
			Potential Querier
	port 50	port 49
	(blocked by STP)
	port 26		port 26
Switch 2:	Rapier 24i		Rapier 24i	Switch 3:
Elected Querier	port 25		port 25	Snooper
	port 2		port 3
	Client 1		Client 2
				igmp-querier.eps

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.

Page 15 AlliedWare™ OS How To Note: IGMP