MAC address

A 'Media Access Control address' or MAC address is a 48-bit identifier used to assign addresses in OSI Layer 2 networks. MAC addresses are assigned by the IEEE, and are used in Ethernet and Token Ring networks.

Since the original designers of Ethernet had the foresight to use a 48 bit address space, there are potentially 2⁴⁸ or 281 million million possible MAC addresses. The IEEE hands out 24-bit OUI prefixes to organizations, effectively allocating blocks of 2²⁴ (around 16 million) MAC addresses at a time.

They are also closely related to NSAP addresses.

External links:

• http://standards.ieee.org/regauth/oui/index.shtml