Cisco WS-C2960-24TC-S Software Guide - Page 393

Configuring the IGMP Throttling Action

Page 393 highlights

Chapter 18 Configuring IGMP Snooping and MVR Configuring IGMP Filtering and Throttling 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 a port can join. Switch(config)# interface gigabitethernet0/2 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 replace the existing group with the new group for which the IGMP report was received 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 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: Step 1 Step 2 Command configure terminal interface interface-id Step 3 ip igmp max-groups action {deny | replace} Purpose Enter global configuration mode. 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 interface. The interface cannot be a trunk port. 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. OL-8603-04 Catalyst 2960 Switch Software Configuration Guide 18-27

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18-27
Catalyst 2960 Switch Software Configuration Guide
OL-8603-04
Chapter 18
Configuring IGMP Snooping and MVR
Configuring IGMP Filtering and Throttling
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 a port can join.
Switch(config)#
interface gigabitethernet0/2
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 replace the existing group with the new group for which the IGMP report was received
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 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
Step 1
configure terminal
Enter global configuration mode.
Step 2
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 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
—Replace the existing group with the new group for which
the IGMP report was received.