MAC address

Overview
Media Access Control addresses (MAC address) are unique identifiers assigned to network interfaces as identifying names. Many network interface cards (NIC) have the MAC permanently stored on a read-only ROM, with the MAC address determined at manufacture time. However, this can be overcome on most hardware through the software method of "MAC Spoofing".

Technical Details
MAC standards are defined by the Institute of Electrical and Electronics Engineers (IEEE) by one of three standards: MAC-48, EUI-48, or EUI-64. Extended Unique Identifier (EUI) is a trademarked name of IEEE.

The original MAC address is defined by IEEE 802, and uses a 48-bit addressing method. There are two types ad addressing schemes: Universally Administered Addresses, and locally administered addresses. Universally Administered Addresses contain 3 octets, used as a unique identify by manufacturer, called Organizationally Unique Identifier (OUI). These two standards are identified by setting the second least-significant digit of the most significant byte of the address to o for universally administered and 1 for local administration. As an example, in the MAC 07:00:00:00:00:01, 07 is the most significant byte (hexadecimal), where its binary equivalent is 00000111, and the second least significant bit is 1. Another option is using unicast, where the intended recipient is only one specific device. In this case, the least significant bit of the most significant octet is set to zero. For example, in 06:00:00:00:00:01, 06 is most significant, the binary form is 00000110, and the least significant bit is a 0, indicating unicast. This will usually only broadcast withing the collision domain, ending at the nearest switch/bridge/router

The term MAC-48 referred to a specific type of EUI-48 (network hardware only), but is not considered to be an antiquated term, replacing it with the EUI-48 term.

The following technologies use MAC-48:
 * Ethernet
 * 802.11
 * Bluetooth
 * IEEE 802.5 token ring
 * FDDI
 * Asynchronous Transfer Mode (ATM)
 * Fibre Channel and Serial Attached SCSI
 * ITU-T G.hn standard
 * most 802 networks

The following technologies use EUI-64:
 * FireWire
 * IPv6
 * ZigBee / 802.15.4 / 6LoWPAN

Links

 * IEEE Std 802-2001
 * EUI Usage Guidelines
 * Standard Group MAC Guidelines
 * Standards for EUI-64