LAN – Local Area Network. This term is used to describe a network within a data centre or building. It is also used to distinguish such a network from one crossing longer distances; a wide-area network or WAN. The main network protocol used in LANs is Ethernet. Every linked device in an Ethernet LAN has a unique 48-bit Media Access Controller (MAC) address. Data is sent out in packets with MAC addresses specifying the source and destination addresses of the packet.