If the number of MAC addresses learned on an interface enabled with port security reaches...

When port security is enabled and the maximum number of learned MAC addresses is reached, the switch can trigger multiple security actions depending on configuration:

Discard packets with unknown source MACs

Generate alarms

Shut down the port (set to error-down)

Do all the above combined (default behavior)

The most comprehensive and commonly configured behavior is error-down + alarm generation, which corresponds to Option D.

Exact Extract - Huawei HCIE-Datacom Switching Guide:

“When the MAC address limit is reached on a port with port security enabled, the system can generate alarms and set the port to error-down state based on security policies.”