In IEEE 802 networks, the Data Link Control (DLC) layer of the OSI Reference Model is divided into two sublayers: the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The Media Access Control (MAC) layer interfaces directly with the network medium. The MAC address is used by the Media Access Control sublayer to identify physical devices. On networks that do not conform to the IEEE 802 standards, the node address maybe called the Data Link Control (DLC) address.

In a local area network (LAN) conforming to the IEEE 802, the MAC (Media Access Control) address is the unique hardware number for an adaptor of a network device such as computer or switch. On an Ethernet LAN, MAC address is called the Ethernet address. MAC addresses are 12-digit hexadecimal numbers (48 bits in length) and are usually written in one of the following two formats:

MM:MM:MM:SS:SS:SS or MM-MM-MM-SS-SS-SS

Whereas MAC addressing works at the data link layer (layer 2), IP addressing functions at the network layer (layer 3). MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter of a network device on a LAN. The MAC address generally remains fixed and stays with the network device regardless where it is installed, but the IP address changes as the network device moves from one network to another and sometimes a dynamic IP address is assigned to a network device.

IP networks maintain a mapping between the IP address of a device and its MAC address. The Address Resolution Protocol (ARP) allows for obtaining this mapping and keeping the ARP cache up to date. Dynamic Host Configuration Protocol (DHCP), which allows a computer to join an IP-based network without having a pre-configured IP address, usually relies on MAC addresses to manage the unique assignment of IP addresses to devices.

All popular network operating systems contain utility programs that allow one to find (and sometimes change) MAC address settings. The table below summarizes options for finding a computer's MAC address.

Related Terms: IP address, ARP, DHCP, Data Link Control