For computers to identify each other on the data link layer, they need a MAC address (hardware address). All devices on a LAN must have a unique MAC address. A MAC address is a 48-bit (six octet) address burned into a network interface card. The first three octets (24 bits) of the MAC address indicate the vendor that manufactured the card. This is called the Organization Unique Identifier (OUI). The last three octets of the MAC address are the unique host address. An example of a MAC address is 00-80-C6-E7-9C-EF.