Layer 2 | 307
MAC Learning Limit
This section describes the following:
• MAC Learning Limit Dynamic
• MAC Learning Limit Station-Move
• Learning Limit Violation Actions
• Station Move Violation Actions
• Recovering from Learning Limit and Station Move Violations
The MAC address learning limit is a method of port security on Layer 2 port-channel and physical
interfaces, and virtual local area networks (VLANs). It allows you to set an upper limit on the number of
MAC addresses that are learned on an interface/VLAN. After the limit is reached, the system drops all
traffic from a device with an unlearned MAC address.
To set a MAC learning limit on an interface, use the following command:
Three options are available with the mac learning-limit command: dynamic, no-station-move, and station-move.
FTOS Behavior: When configuring the MAC learning limit on a port, the configuration is accepted
(becomes part of the running-config and show mac learning-limit interface) before the system verifies that
sufficient content addressable memory (CAM) space exists. If the CAM check fails, a message is
displayed:
%E90MH:5 %ACL_AGENT-2-ACL_AGENT_LIST_ERROR: Unable to apply access-list
Mac-Limit on TenGigabitEthernet 5/84
In this case, the configuration is still present in the running-config and the show output. Remove the
configuration before re-applying a MAC learning limit with a lower value. Also, ensure that you can
view the syslog message on your session.
Task Command Syntax Command Mode
Specify the number of MAC addresses that the system
can learn off a Layer 2 interface.
mac learning-limit address_limit
INTERFACE
Note: A simple network management protocol (SNMP) trap is available for mac learning-limit station-move.
No other SNMP traps are available for the MAC learning limit, including limit violations.
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