9.4 Optional IP Multicast Routing Tasks
9.6.4
Change IGMP versions
Cisco routers do not automatically detect the IGMP version of systems on the subnet and dynamically switch between versions. If some hosts on the subnet support only IGMPv1, then the DR must be configured for IGMPv1. However, when the router is statically configured for IGMPv1, the router will ignore any IGMPv2 leave group messages that the router receives from any IGMPv2 hosts on the same subnet.

IGMP Version 2 mode is the default for all systems using Cisco IOS Release 11.3(2)T or later. To determine the current version setting for an interface, enter the following command in privileged EXEC mode.

Router#show ip igmp interface type-number

Where type-number represents the name of the interface on which the IGMP protocol is configured.

An example of this command is shown in the figure to the left.

If you must reenable IGMP Version 2 or specify IGMP Version 1, enter the following command in interface configuration mode.

Router(config-if)#ip igmp version {2 | 1}

To restore the default value of Version 2, enter the no ip igmp version command.