A Firewall is a part of a computer system designed to block or permit network communication based on set of predefined rules. The design and operation of the Internet is based on the Internet Protocol Suite, also commonly called Transfer Control Protocol / Internet Protocol (TCP/IP). In this system, hosts and host services are referenced using two components: an address and a port number. For example, HTTP—standard web protocol uses port 80 by default. In general, most services use a limited number of ports. A common technique for detecting running services on a public server is port scanning. It is used by administrators for verification of their security policies and by hackers for obtaining lists of potential targets for later attack. To prevent this and other types of misuse we should block access to all ports except the ones...