Cisco Catalyst 4500 Series, Software Configuration Manual

Page: 208 / 2086

4-30
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 4 Administering the Switch
Managing the MAC Address Table
When PVLANs are configured, address learning depends on the type of MAC address:
• Dynamic MAC addresses learned in one VLAN of a PVLAN are replicated in the associated
VLANs. For example, a MAC address learned in a private-VLAN secondary VLAN is replicated in
the primary VLAN.
•
Static MAC addresses configured in a primary or secondary VLAN are not replicated in the
associated VLANs. When you configure a static MAC address in a PVLAN primary or secondary
VLAN, you should also configure the same static MAC address in all associated VLANs.
For more information about PVLANs, see Chapter 47, “Configuring Private VLANs.”
Default MAC Address Table Configuration
Table 4-4 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. 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.
To configure the dynamic address table aging time, perform this task:
Table 4-4 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
Enters global configuration mode.
Step 2
mac address-table aging-time
[
0
|
10-1000000
] [
vlan vlan-id
]
Sets the length of time that a dynamic entry remains in the MAC
address table after the entry is used or updated.
To return to the default value, use the no mac address-table
aging-time global configuration command.
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 , valid IDs are 1 to 4094.
Step 3
end
Returns to privileged EXEC mode.