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When port security is enabled, MAC addresses are detected but after a short while the port is shut down due to restrictive port security configuration


Core issue

The port security feature is used to restrict input to an interface by limiting and identifying MAC addresses of the workstations that are allowed to access the port.

Port security voilations occur when the following happens:

  • maximum number of secure MAC addresses is reached
  • MAC address of a workstation attempting to access the port is different from any of the identified secure MAC addresses
  • workstation with a secure MAC that is address configured or learned on    one secure port attempts to access another secure port


To troubleshoot port security violations, perform the following steps:

  • Changed the violation mode to restrict or protect if the default shutdown mode is not desired.

  • Sniff the LAN and verify there is not an unauthorized device attempting to access the secured port, causing shutdown due to violation.

  • Verify that a MAC address secured on another port is not attempting    access to a different secured port.

  • Verify that maximum number of secure MAC addresses is not exceeded.

  • Verify that NIC cards on clinets are not faulty, sending erroneous MAC adderesses.

For additional information, refer to Port Security.

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