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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 5 Administering the Switch
Managing the MAC Address Table
If the switch is running the metro IP access or metro access image, you can disable MAC address
learning on a per-VLAN basis. Customers in a service provider network can tunnel a large number of
MAC addresses through the network and fill up the available MAC address table space. You can control
MAC address learning on a VLAN and manage the MAC address table space that is available on the
switch by controlling which VLANs, and therefore which ports, can learn MAC addresses.
Before you disable MAC address learning, be sure that you are familiar with the network topology and
the switch system configuration. Disabling MAC address learning on a VLAN could cause flooding in
the network. See the “Disabling MAC Address Learning on a VLAN” section on page 5-26 for more
information.
Default MAC Address Table Configuration
Table 5-3 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. 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.
Table 5-3 Default MAC Address Table Configuration
Feature Default Setting
Aging time 300 seconds
Dynamic addresses Automatically learned
Static addresses None configured
MAC address learning on VLANs Enabled