One of the important parts of a computer network, a firewall is necessary to prevent the unauthorized access to the system. Implementing a firewall is significant to avoid security breach as well as to prevent data corruption that is usually caused by accessing harmful sites. Aside from these, it is also important to filter messages in intranets. To extend our understanding on this special and useful computer architecture, it is best to have a closer look at the functions of this appliance as well as the different kinds of firewall techniques that can be used to enhance the security features of a network.