MAC Address Aging

A mac address aging timer determines when an entry will age out and be removed from the mac address table.?

The age timer range is from 0 to 1000000, and the default value for Cisco switches is 300 seconds, which means that if the switch has learned some mac addresses but those users are not communicating, then the switch will delete those entries after 300 seconds.

You can also disable that aging by setting the value to 0. As I said by default the value is 300, so there are scenarios in which your mac address table will be deleted.

Aging and getting deleted are two different things. Whenever your switch boots up, mac address entries will be deleted, but if the switch is up and mac address entries are not in use, they will age out.

The following command can be used to check the mac-address aging time on Cisco switches.

show mac address-table aging-time
        

Types of the aging timer in switches:

1. Global aging timer: Time after which all learned MAC addresses are flushed.
2. Per VLAN aging timer: The time period after which MAC addresses belonging to a specific VLAN are flushed.