# MAC Address **A unique identifier assigned to network interface controllers for use in [[medium access control]].** A **[[medium access control]] address** or **MAC address** is a unique identifier assigned to the *network interface controllers* of devices such that they can be identified in medium access control. MAC addresses are mainly assigned to devices by their manufacturers and are thus often also referred to as the **burned-in** or **physical address**. Every network interface, regardless of whether they are of the same device, in the same network segment must have a unique MAC address. In IPv4, the MAC address of a network interface is translated from its associated [[IP address]] through the [[Address Resolution Protocol]]. ## Address format ![[MediumAccessControlAddress.svg]] *A MAC address consists of six octets which can be divided into two groups of three, the first forming the organisationally unique identifier* MAC addresses typically consist of six groups or octets of two hexadecimal numerals each, separated by a hyphen. The first three groups form the *organisationally unique identifier* of the manufacturer of the device while the last three groups are uniquely assigned by the manufacturer per device. ### Individual/Group bit The *last bit* of the first octet is the **Individual/Group** or **I/G bit** which identifies whether a frame is being transmitted unicast or multicast. - if the bit is *zero*, the frame is transmitted *unicast* and intended to be received by only one network interface. - if the bit is *one*, the frame is transmitted *multicast* and intended to be received by a group of network interfaces configured to receive certain multicast addresses. ### Universal/Local Bit The *second last bit* of the first octet is the **Universal/Local** or **U/L bit** which identifies whether the address is universally or locally administrated. - if the bit is *zero*, the MAC address is *universally* administrated. - if the bit is *one*, the MAC address is *locally* administrated.