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Catalyst 2940 Switch Software Configuration Guide
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Chapter16 Configuring IGMP Snooping and MVR
Configuring IGMP Filtering and Thrott li ng
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If you configure the throttling action as deny, the en tries t hat were pre v iously i n the f orwa rding
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 deletes a randomly selected entry and adds an entry for the next IGMP r eport recei ved
on the interface.
To prevent the switch from removing the forwarding-table entries, you can configure t he IG M P
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:
To return to the default action of dropping the report, use the no ip igmp max-groups action interface
configuration command.
This example shows how to configure an interface to remove a randomly selected multicast entry in the
forwarding table and to add an IGMP group to the forwarding table if the maximum number of entries
is in the table.
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# ip igmp max-groups action replace
Switch(config-if)# end
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 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.
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—Remove a randomly selected multicast entry in the
forwarding table, and add the IGMP group in the report.
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.