Internet Group Management Protocol | 4112. When a router receives a query it compares the IP address of the interface on which it was receivedwith the source IP address given in the query. If the receiving router IP address is greater than thesource address given in the query, the router stops sending queries. By this method, the router with thelowest IP address on the subnet is elected querier and continues to send queries.3. If a specified amount of time elapses during which other routers on the subnet do not receive a query,those routers assume that the querier is down, and a new querier is elected.The amount of time that elapses before routers on a subnet assume that the querier is down is the OtherQuerier Present Interval. Adjust this value using the command ip igmp querier-timeout from INTERFACEmode.Configuring a Static IGMP GroupConfigure a static IGMP group using the command ip igmp static-group. Multicast traffic for static groupsis always forwarded to the subnet even if there are no members in the group.View the static groups using the command show ip igmp groups from EXEC Privilege mode. Static groupshave an expiration value of Never and a Last Reporter value of CLI, as shown in Figure 19-8.Enabling IGMP Immediate-leaveIf the querier does not receive a response to a group-specific or group-and-source query, it sends another(Querier Robustness Value). Then, after no response, it removes the group from the outgoing interface forthe subnet.IGMP Immediate Leave reduces leave latency by enabling a router to immediately delete the groupmembership on an interface upon receiving a Leave message (it does not send any group-specific orgroup-and-source queries before deleting the entry). Configure the system for IGMP Immediate Leaveusing the command ip igmp immediate-leave.View the enable status of this feature using the command show ip igmp interface from EXEC Privilegemode, as shown in Figure 19-7.Note: The timeout value for an IGMP querier is calculated differently on Dell Force10 FTOS routers thanon Cisco IOS routers. As a result, if the IGMP querier in a subnet goes down, a Cisco IOS router may beelected as the new querier before a Dell Force10 FTOS router.
