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Catalyst 2960 Switch SoftwareConfiguration Guide
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Chapter20 Configuring IGMP Snooping and MVR
Configuring IGMP Filtering and Thrott ling
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.
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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 n ext IGMP report received on
the interface.
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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 forwar ding table,
the switch replaces a randomly selected entry with the received IGMP report.
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
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the physical interface to be configured, and enter interface
configuration mode. The interface can be a Layer 2 port that does not
belong to an EtherChannel group or an EtherChannel in terface. The
interface cannot be a trunk port.
Step3 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—Replace the existing group with the new group for which
the IGMP report was received.
Step4 end Return to privileged EXEC mode.
Step5 show running-config interface
interface-id
Verify the configuration.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.