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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 7 Administering the Switch
Managing the MAC Address Table
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).
To verify that dynamic entries have been removed, use the show mac address-table dynamic privileged
EXEC command.
Configuring MAC Address Notification Traps
MAC address notification enables you to track users on a network by storing the MAC address activity
on the switch. Whenever the switch learns or removes a MAC address, an SNMP notification can be
generated and sent to the NMS. If you have many users coming and going from the network, you can set
a trap interval time to bundle the notification traps and reduce network traffic. The MAC notification
history table stores the MAC address activity for each hardware port for which the trap is enabled. MAC
address notifications are generated for dynamic and secure MAC addresses; events are not generated for
self addresses, multicast addresses, or other static addresses.
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.