Users Guide

3. Sticky secure MAC addresses are learned dynamically but are saved in the running configuration. Secure sticky MAC
addresses never age out.
After you enable port security on an interface, by default, the maximum number of MAC address that the interface can learn
is one. This is applicable for both dynamic and static secure MAC addresses. After you enable port security on an interface, by
default, sticky MAC addresses and MAC movement are disabled on the interface.
MAC address learning limit
Using the MAC address learning limit method, you can set an upper limit on the number of allowed MAC addresses on an
interface. Limiting the MAC addresses protects switches from MAC address flooding attacks. After the configured limit is
reached on an interface, by default, the system drops all traffic from any unknown device.
When you configure MAC address learning limit, ensure that the number of static MAC addresses present on the system is not
greater than the MAC address learning limit that you configure. If the number of dynamically-learned MAC addresses is greater
than your MAC address limit, the system flushes all dynamically-learned MAC addresses.
You can configure an interface to learn a maximum of 3072 MAC addresses. You can also disable the MAC address learning
limit feature so that the interface can learn the maximum number MAC addresses that the system supports. Disabling the MAC
address learning limit feature does not remove the previously learned or configured secure MAC addresses.
MAC address movement
A MAC address movement happens when the system detects the same MAC address on an interface which it has already
learned through another port security-enabled interface on the same broadcast domain. MAC address movement is not allowed
for secure static and sticky MAC addresses. By default, MAC address movement for dynamically-learned MAC address is
disabled on the system.
Secure dynamic MAC address movement is allowed between port-security-enabled and port-security-disabled interfaces.
Sticky MAC addresses
When you reload the system, port security removes the dynamically learned secure MAC addresses. You can use the sticky
feature to make the dynamically learned secure MAC addresses persist even after a system reboot so that the interface
does not have to learn these MAC addresses again. Use the copy running-configuration startup-configuration
command to save the sticky secure MAC addresses.
When you enable sticky MAC address learning on an interface, all existing dynamically-learned MAC addresses and MAC
addresses that are learned in the future are converted to sticky MAC addresses.
To enable sticky MAC address learning on an interface, ensure that the mac learn no-limit command is not configured.
Port security violations
There are two types of port security violations.
● Mac address learning limit violation
● Mac address move violation
Mac address learning limit violation
After the number of secure MAC address reaches the maximum configured, if an interface receives a frame with the source
MAC address different from any of the learned MAC addresses, the system considers this as a MAC address learning limit
violation.
You can configure MAC address learning limit violation actions.
● log — The system drops the packet and displays a log message with the VLAN, interface, and the source MAC address
that caused the violation.
● drop — The system drops the packet and does not display a log message.
● forward — The system forwards the packet without learning the source MAC address or displaying a log message.
● shutdown — The system shuts down the port.
Mac address move violation
If the system detects the same MAC address in a port-security-enabled interface which it has already learned through another
port-security-enabled interface, by default, the system considers this as a MAC address move violation. You can configure
MAC address move violation actions. You can also configure the system to permit MAC address movement across port
security-enabled interfaces.
You can configure MAC address move violation actions.
● log — The system drops the packet and displays a log message with the VLAN, interface, and the source MAC address
that caused the violation.
● drop — The system drops the packet and does not display a log message.
Security
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