|  |  | A Media Access Control (MAC) address is the physical address, also called the layer two address, configured in a Network Interface Card (NIC). MAC address lock down: catalyst Ethernet switches block access to a MAC address that has not been configured or learned for the switch. In a lock down, the port is disabled after the unauthorized MAC address attempts access. The LED for the port changes from green to orange, which signifies a link down state and prevents anyone from putting an unauthorized PC on the network.