Default Mac Address Table Configuration; Changing The Address Aging Time; Removing Dynamic Address Entries - Cisco Catalyst 3750 Software Configuration Manual

Managing the MAC Address Table
Table 5-3
Feature
Aging time
Dynamic addresses
Static addresses

Changing the Address Aging Time

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. Flooding results, which can impact switch performance.
Beginning in privileged EXEC mode, follow these steps to configure the dynamic address table aging
time:
Command
Step 1 configure terminal
Step 2
mac address-table aging-time [0 |
10-1000000] [vlan vlan-id]
Step 3
end
Step 4
show mac address-table aging-time
Step 5 copy running-config startup-config
To return to the default value, use the no mac address-table aging-time global configuration command.

Removing Dynamic Address Entries

To remove all dynamic entries, use the clear mac address-table dynamic command in privileged EXEC
mode. You can also remove a specific MAC address (clear mac address-table dynamic address
mac-address), remove all addresses on the specified physical port or port channel (clear mac
address-table dynamic interface interface-id), or remove all addresses on a specified VLAN (clear
mac address-table dynamic vlan vlan-id).
To verify that dynamic entries have been removed, use the show mac address-table dynamic privileged
EXEC command.
Catalyst 3750 Metro Switch Software Configuration Guide
5-22

Default MAC Address Table Configuration

Default Setting
300 seconds
Automatically learned
None configured
Purpose
Enter global configuration mode.
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, the range is 1 to 4094.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 5 Administering the Switch
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