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Changing the MAC Address Aging Time

May 27, 2008 By Leave a Comment

Dynamic addresses are source MAC addresses that the switch learns and then ages when they are not in use. You can change the aging time setting for all VLANs or for a specified VLAN.  Setting too short an aging time can cause addresses to be prematurely removed from the table. Then when the switch receives a packet for an unknown destination, it floods the packet to all ports in the same VLAN as the receiving port. This unnecessary flooding can impact performance. Setting too long an aging time can cause the address table to be filled with unused addresses, which prevents new addresses from being learned.

Beginning in privileged EXEC mode, follow these steps to configure the dynamic address table aging time:

 

 

Command

Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

mac address-table aging-time [0 | 10-1000000] [vlan vlan-id]

Set the length of time that a dynamic entry remains in the MAC address table after the entry is used or updated.

The range is 10 to 1000000 seconds. The default is 300. You can also enter 0, which disables aging. Static address entries are never aged or removed from the table.

For vlan-id, valid IDs are 1 to 4094.

Step 3 

end

Return to privileged EXEC mode.

Step 4 

show mac address-table aging-time

Verify your entries.

Step 5 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

 

To return to the default value, use the no mac address-table aging-time global configuration command.

Administering the Catalyst Switch

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