What is the MAC address?

Each network interface card (NIC) has a unique ‘MAC address’ assigned to it. The MAC address, also referred to as the ‘physical address,’ is a 6-byte (48-bit), hexadecimal serial number hard-coded onto the card by the manufacturer.

A NIC manufacturer (e.g., Intel, 3Com, Cisco, etc.) must apply to the IEEE (institute of Electrical and Electronics Engineers) for a block of addresses to assign to its cards. The leftmost 3 octets of the address identify the manufacturer and the rightmost 3 octets represent the unique serial number for the card.

If your system is running TCP/IP, you can learn your MAC address by going to a command prompt and typing IPCONFIG /ALL (Windows NT) or WINIPCFG (Windows 95). Shown below is a portion of the information returned by the IPCONFIG /ALL command showing the MAC (physical) address of a NIC:

Note that the name ‘MAC’ stands for Media Access Control, a division of the Data Link layer under the IEEE 802 model. Thus, ‘MAC address’ is something of a misnomer. The MAC address is referenced at this layer but actually resides at the physical layer. Although ‘physical address’ is the more accurate description, ‘MAC address’ is the term most often used in practice.