Computer network is the network which can result in the communication between the devices and the computer systems. There are various applications of computer networks like in scientific and engineering disciplines. The three main applications of computer networks include Local Area Network (LAN), Wide Area Network (WAN) and Wireless LAN and WANs. Computer networks in small geographic area are used in the form of LAN. For a large geographical area WAN technology is used. Computer networks are widely used in buildings and business units to make subunits. Similarly, intranet and extranet technologies are used in the business organizations which are also the applications of computer networks.