What is a MAC Address
Almost every network adaptor has a unique identifier. This identifier is call a MAC (Media Access Control) address which is designed to be globally unique. The MAC address consists of a manufacturers ID followed by a device number that is unique for that manufacturer.
A standard MAC address consists of is 48 bits (6 bytes) and is officially referred to as MAC-48. There are also two other versions of numbering. These are EUI-48 and EUI-64. EUI is an abbreviation of Extended Unique Identifier. EUI-48 addresses are similar to MAC-48 addresses and even use the same number space. EUI-64 addresses contain 8 bytes (64 bits). With all three numbering systems, the first three bytes identify the manufacturer. With MAC-48 and EUI-48 the remaining 3 bytes identify the individual device (these bytes are assigned by the manufacturer to uniquely identify their own devices). With EUI-64, the remaining five bytes are used by the manufacturer to identify the device.
MAC addresses (and EUI-48 addresses) are displayed as 6 groups of 2 hexadecimal digits (eg. FF-F0-89-AE-05-CO). EUI-64 addresses are usually displayed in a similar format, with the addition of the 2 extra bytes.
MAC addresses are used to uniquely identify network hosts. For example, DHCP uses MAC addresses to track which network device is assigned which IP address.