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.