Reference Guide

Adjusting the IGMP Querier Timeout Value
If there is more than one multicast router on a subnet, only one is elected to be the querier, which is the router that sends
queries to the subnet.
1. Routers send queries to the all multicast systems address, 224.0.0.1. Initially, all routers send queries.
2. When a router receives a query, it compares the IP address of the interface on which it was received with the source IP
address given in the query. If the receiving router IP address is greater than the source address given in the query, the
router stops sending queries. By this method, the router with the lowest 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 other querier present
interval.
● Adjust the other querier present interval.
INTERFACE mode
ip igmp querier-timeout
Configuring a Static IGMP Group
To configure and view a static IGMP group, use the following commands.
Multicast traffic for static groups is always forwarded to the subnet even if there are no members in the group.
Static groups have an expiration value of Never and a Last Reporter value of CLI, as shown in the example in Viewing IGMP
Groups.
● Configure a static IGMP group.
INTERFACE mode
ip igmp static-group
● View the static groups.
EXEC Privilege mode.
show ip igmp groups
Enabling IGMP Immediate-Leave
If 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 for the subnet.
IGMP immediate leave reduces leave latency by enabling a router to immediately delete the group membership on an interface
after receiving a Leave message (it does not send any group-specific or group-and-source queries before deleting the entry).
● Configure the system for IGMP immediate leave.
ip igmp immediate-leave
● View the enable status of the IGMP immediate leave feature.
EXEC Privilege mode
show ip igmp interface
View the enable status of this feature using the command from EXEC Privilege mode, as shown in the example in Selecting an
IGMP Version.
326
Internet Group Management Protocol (IGMP)