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Catalyst 2940 Switch Software Configuration Guide
78-15507-02
Chapter 16 Configuring IGMP Snooping and MVR
Configuring IGMP Filtering and Throttling
Setting the Maximum Number of IGMP Groups
You can set the maximum number of IGMP groups that a Layer 2 interface can join by using the ip igmp
max-groups interface configuration command. Use the no form of this command to set the maximum
back to the default, which is no limit.
You can use this command on an logical EtherChannel interface but cannot use it on ports that belong to
an EtherChannel port group.
Beginning in privileged EXEC mode, follow these steps to set the maximum number of IGMP groups in
the forwarding table:
To remove the maximum group limitation and return to the default of no maximum, use the no ip igmp
max-groups interface configuration command.
This example shows how to limit to 25 the number of IGMP groups that an interface can join.
Switch(config)# interface fastethernet0/4
Switch(config-if)# ip igmp max-groups 25
Switch(config-if)# end
Configuring the IGMP Throttling Action
After you set the maximum number of IGMP groups that a Layer 2 interface can join, you can configure
an interface to remove a randomly selected multicast entry in the forwarding table and to add the next
IGMP group to it by using the ip igmp max-groups action replace interface configuration command.
Use the no form of this command to return to the default, which is to drop the IGMP join report.
Follow these guidelines when configuring the IGMP throttling action:
• You can use this command on a logical EtherChannel interface but cannot use it on ports that belong
to an EtherChannel port group.
• When the maximum group limitation is set to the default (no maximum), entering the ip igmp
max-groups action {deny | replace} command has no effect.
• If you configure the throttling action and set the maximum group limitation after an interface has
added multicast entries to the forwarding table, the forwarding-table entries are either aged out or
removed, depending on the throttling action.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and enter the physical interface to
configure, for example gigabitethernet0/1. The interface can be a
Layer 2 port that does not belong to an EtherChannel group or a
EtherChannel interface.
Step 3
ip igmp max-groups number Set the maximum number of IGMP groups that the interface can join.
The range is from 0 to 4294967294. The default is to have no maximum
set.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-configuration interface
interface-id
Verify the configuration.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.