Mac Address-Table Learning - Cisco ME 3800X Command Reference Manual

Chapter 2 Cisco ME 3800X and ME 3600X Switch Cisco IOS Commands

mac address-table learning

To enable MAC address learning on a VLAN or bridge domain, use the mac address-table learning
command in global configuration mode. This is the default state. To disable MAC address learning to
control which VLANs or bridge domains can learn MAC addresses, use the no form of this command.
Syntax Description
bridge-domain
domain-id
vlan vlan-id
Defaults By default, MAC address learning is enabled on all VLANs and bridge domains.
Command Modes Global configuration
Command History Release
12.2(52)EY
Usage Guidelines Customers in a service provider network can tunnel a large number of MAC addresses through the
network and fill the available MAC address table space. When you control MAC address learning on a
VLAN or bridge domain, you can manage the available MAC address table space by controlling which
VLANs or bridge domains, and therefore which ports, can learn MAC addresses.
You can disable MAC address learning on a VLAN or bridge domain by entering the no mac
address-table learning {vlan vlan-id | bridge-domain domain-id} command.
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 could cause flooding in the network.
For example, if you disable MAC address learning on a VLAN with a configured switch virtual interface
(SVI), the switch floods all IP packets in the Layer 2 domain. If you disable MAC address learning on a
VLAN that includes more than two ports, every packet entering the switch is flooded in that VLAN
domain. We recommend that you disable MAC address learning only in VLANs that contain two ports
and that you use caution before disabling MAC address learning on a VLAN with an SVI.
To display MAC address learning status or all VLANs and bridge domains, enter the show
mac-address-table learning command. To display for a specific VLAN or bridge domain, enter the
show mac address-table learning [bridge-domain number] [vlan vlan-id] command.
Examples This example shows how to disable MAC address learning on VLAN 2003:
Switch(config)# no mac address-table learning vlan 2003
OL-28238-01
mac address-table learning {vlan vlan-id | bridge-domain domain-id}
no mac address-table learning {vlan vlan-id | bridge-domain domain-id}
Specifies MAC address learning per bridge domain. The bridge domain ID
range is from 1 to 8000.
Specifies MAC address learning per VLAN. Valid VLAN IDs are 1 to 4094.
Modification
This command was introduced.
Cisco ME 3800X and ME 3600X Switch Command Reference
mac address-table learning
2-151