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: