A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model. MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card?s read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer?s registered identification number. It may also be known as an Ethernet hardware address (EHA), hardware address, adapter address, or physical address.