The Media access layer is one of the layers of the OSI reference model. It is concerned with the access to the physical network medium. Devices that access this medium need to be identified. For this reason, many network technologies, amongst them Ethernet use unique addresses, to identify the network card, which is used to access the medium. These addresses are usually called the Media Access Control address or MAC address.
Each device is assigned a MAC address by its manufacturer. The original Xerox Ethernet addressing scheme still used to assign MAC addresses. It allows MAC addresses to be 48-bits long. So, there are 248 or 281,474,976,710,656 possible MAC addresses.
- IEEE Std 802-2001. The Institute of Electrical and Electronics Engineers, Inc. (IEEE). 2002-02-07. p. 19. ISBN 0-7381-2941-0. http://standards.ieee.org/getieee802/download/802-2001.pdf. Retrieved 2011-09-08. "The universal administration of LAN MAC addresses began with the Xerox Corporation administering Block Identifiers (Block IDs) for Ethernet addresses."