At the most fundamental level, manufacturers assign each networking component a media access control (MAC) address at the time of manufacturing. The MAC address is embedded in the firmware of the network component, and it serves to identify both the manufacturer and the component itself. Security policies often include MAC addresses to ensure that only authorized devices can connect to the network.

A given computer may have multiple MAC addresses, depending on the number of networking components it has installed. For example, a notebook computer that has Bluetooth, WiFi, and Ethernet adapters will have three separate MAC addresses, although the network will see only the component that is currently connected to the network.

In addition, because the MAC address is associated with the networking component rather than with the computer itself, it is possible for a computer to get a new MAC address if its network card is replaced for some reason.