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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 7 Administering the Switch
Managing the MAC Address Table
Default MAC Address Table Configuration
Table 7-3 shows the default MAC address table configuration.
Changing the Address Aging Time
Dynamic addresses are source MAC addresses that the switch learns and then ages when they are not in
use. The aging time parameter defines how long the switch retains unseen addresses. This parameter
applies to all VLANs.
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:
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).
Table 7-3 Default MAC Address Table Configuration
Feature Default Setting
Aging time 300 seconds
Dynamic addresses Automatically learned
Static addresses None configured
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
mac address-table aging-time [0 |
10-1000000]
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.
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.
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