Reference Guide

Viewing IGMP Groups
To view both learned and statically configured IGMP groups, use the following command.
● View both learned and statically configured IGMP groups.
EXEC Privilege mode
show ip igmp groups
Dell(conf-if-te-1/0)#do show ip igmp groups
Total Number of Groups: 2
IGMP Connected Group Membership
Group Address Interface Uptime Expires Last Reporter
224.1.1.1 GigabitEthernet 1/0 00:00:03 Never CLI
224.1.2.1 GigabitEthernet 1/0 00:56:55 00:01:22 1.1.1.2
Adjusting Timers
The following sections describe viewing and adjusting timers.
To view the current value of all IGMP timers, use the following command.
● View the current value of all IGMP timers.
EXEC Privilege mode
show ip igmp interface
For more information, refer to the example shown in Viewing IGMP Enabled Interfaces.
Adjusting Query and Response Timers
The querier periodically sends a general query to discover which multicast groups are active. A group must have at least one
host to be active.
When a host receives a query, it does not respond immediately, but rather starts a delay timer. The delay time is set to a random
value between 0 and the maximum response time. The host sends a response when the timer expires; in version 2, if another
host responds before the timer expires, the timer is nullified, and no response is sent.
The maximum response time is the amount of time that the querier waits for a response to a query before taking further action.
The querier advertises this value in the query (refer to the illustration in IGMP Version 2). Lowering this value decreases leave
latency but increases response burstiness because all host membership reports must be sent before the maximum response time
expires. Inversely, increasing this value decreases burstiness at the expense of leave latency.
When the querier receives a leave message from a host, it sends a group-specific query to the subnet. If no response is
received, it sends another. The amount of time that the querier waits to receive a response to the initial query before sending a
second one is the last member query interval (LMQI). The switch waits one LMQI after the second query before removing the
group from the state table.
● Adjust the period between queries.
INTERFACE mode
ip igmp query-interval
● Adjust the maximum response time.
INTERFACE mode
ip igmp query-max-resp-time
● Adjust the last member query interval.
INTERFACE mode
ip igmp last-member-query-interval
Internet Group Management Protocol (IGMP)
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