Administrator 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
show ipv6 mld groups
DellEMC#show ip igmp groups
Total Number of Groups: 2
IGMP Connected Group Membership
Group Address Interface Mode Uptime Expires Last Reporter
225.1.1.1 GigabitEthernet 1/1 IGMPV2 00:11:19 00:01:50 165.87.34.100
225.1.2.1 GigabitEthernet 1/1 IGMPV2 00:10:19 00:01:50 165.87.31.100
Dell#show ipv6 mld groups
Total Number of Groups: 1
MLD Connected Group Membership
Group Address Interface Mode Uptime Expires Last Reporter
Ff08::12 Vlan 10 MLDv2 00:00:12 00:02:05 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 time period between queries used to discover IPv6 multicast groups.
Interface mode
ipv6 mld query-interval
• Adjust the maximum response time.
INTERFACE mode
ip igmp query-max-resp-time
• Adjust the maximum amount of time that the querier waits, for an IPv6 query response, before taking further action.
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Internet Group Management Protocol (IGMP)