Reference Guide

556 | Internet Group Management Protocol (IGMP)
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• IGMP snooping reacts to Layer 2 topology changes triggered by MSTP by sending a general query
on the interface that comes in FWD state.
Important Points to Remember for IGMP Querier
• The IGMP snooping Querier supports version 2.
• You must configure an IP address to the VLAN interface for IGMP snooping Querier to begin.
The IGMP snooping Querier disables itself when a VLAN IP address is cleared, and then it
restarts itself when an IP address is re-assigned to the VLAN interface.
• When enabled, IGMP snooping Querier will not start if there is a statically configured multicast
router interface in the VLAN.
• When enabled, IGMP snooping Querier starts after one query interval in case no IGMP general
query (with IP SA lower than its VLAN IP address) is received on any of its VLAN members.
• When enabled, IGMP snooping Querier periodically sends general queries with an IP source
address of the VLAN interface. If it receives a general query on any of its VLAN member, it will
check the IP source address of the incoming frame.
If the IP SA in the incoming IGMP general query frame is lower than the IP address of
the VLAN interface, then the switch disables its IGMP snooping Querier functionality.
If the IP SA of the incoming IGMP general query is higher than the VLAN IP address,
the switch will continue to work as an IGMP snooping Querier.
ip igmp snooping enable
c e s
Enable IGMP snooping on all or a single VLAN. This is the master on/off switch to enable IGMP
snooping.
Syntax
ip igmp snooping enable
To disable IGMP snooping, enter no ip igmp snooping enable command.
Defaults
Disabled
Command Modes
CONFIGURATION
INTERFACE VLAN
Command
History
Usage
Information
You must enter this command to enable IGMP snooping. When enabled from CONFIGURATION
mode, IGMP snooping is enabled on all VLAN interfaces (except default VLAN).
Related
Commands
Version 7.6.1.0 Introduced on S-Series
Version 7.5.1.0 Introduced on C-Series
E-Series legacy command
Note: You must execute the no shutdown command on the VLAN interface for IGMP
Snooping to function.
no shutdown Activate an interface