Specifications

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Catalyst 2970 Switch Software Configuration Guide
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Chapter 18 Configuring IGMP Snooping and MVR
Configuring IGMP Filtering and Throttling
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.
– If you configure the throttling action as deny, the entries that were previously in the forwarding
table are not removed but are aged out. After these entries are aged out and the maximum
number of entries is in the forwarding table, the switch drops the next IGMP report received on
the interface.
– If you configure the throttling action as replace, the entries that were previously in the
forwarding table are removed. When the maximum number of entries is in the forwarding table,
the switch deletes a randomly selected entry and adds an entry for the next IGMP report received
on the interface.
To prevent the switch from removing the forwarding-table entries, you can configure the IGMP
throttling action before an interface adds entries to the forwarding table.
Beginning in privileged EXEC mode, follow these steps to configure the throttling action when the
maximum number of entries is in the forwarding table:
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. The interface can be a Layer 2 port that does not belong to an
EtherChannel group or an EtherChannel interface. The interface cannot
be a trunk port.
Step 3
ip igmp max-groups action {deny |
replace}
When an interface receives an IGMP report and the maximum number
of entries is in the forwarding table, specify the action that the interface
takes:
• deny—Drop the report.
• replace—Remove a randomly selected multicast entry in the
forwarding table, and add the IGMP group in the report.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-config interface
interface-id
Verify the configuration.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.