The connection of an internal network to an external network such as Internet has made it vulnerable to attacks. One class of network attack is unauthorized penetration into network due to the openness of networks. It is possible for an attacker or hackers to sum access to an internal network, this pose great danger to the network and network resources. Our objective and major concern of network design was to build a secured network, based on software firewall that ensured the integrity and confidentiality of information on the network. We proposed an Object-Oriented Methodology and developed an improved software based solution that allows all the inbound and outbound traffic to pass through the firewall. The firewall in turn determines which traffic should be allowed in or out of the network. The firewall algorithm was implemented using Java programming language, which was based on java security architecture. It also utilizes the concept of XML and HTML programming which enables network communication over the Internet.

Chapter 1: Introduction

  1.  Introduction

Computer network is the engineering discipline concerned with communication between computer system and devices. The purposes of networking are exchange of data and resources sharing. With network, large volume of data can be exchanged through both short and long-range connections. Likewise computer resources such as hardware (printers, scanner etc.) and software can be remotely shared among network hosts.

     With increase reliance on computer network, calls for serious monitoring of the traffic in and out of the system network. Attackeron the internet could break into the network and do harm in a number of ways; they can steal or damage important data, damage individuals computer or their entire network, and use the internal network computer resources. Due to some of these security threats, there was the need to build a defensive mechanism that ensures that attackers and their likes are not allowed into the network. Firewalls are designed to stop unwanted or suspected traffics from flowing into the internal network. Sets of rules are applied to control the type of networking traffic flowing in and out of the system. This would ensure that attackers have no access to the internal network.

      This thesis is organized in four chapters. Chapter 2 provides theoretical background information about firewalls, roles, controls and their impact in network security; a comprehensive literature review on how network traffic can be monitored in order to prevent an unauthorized access to internal network. Chapter 3, we proposed and developed an improved software based solution that allows all the inbound and outbound traffic to pass through the firewall which, in turn determines which traffic should be allowed in or out of the network using object-oriented methodology. Chapter 4, Firewall security system was implementation using software-based solution. The use of Java programming language and the concept of xml and html programming were considered in order to achieve our objectives.

1.1 Statement of Problem

The problem to be solved is the problem of organizations network. What can firms do to protect their network over potential threats against the “resources” they share on the network?

1.2 Objectives

  1. To developed a firewall system to block unauthorized access to the network and prevent malicious attack which could lead to data loss
  2. To build a secured network, based on software firewall to protect network resources and ensured the integrity and confidentiality of information on the network are not compromised

1.3 Significance of the Study

The significance of this study is to show how a firewall could prevent attack and protect network resources which will make harder for an attacker to penetrate into the system. The system will be able to offer online services. The probability of exploring vulnerability will be reduced to low risk and the system will be more stable

Chapter 2: Literature Review

2.0 Introduction

This chapter describes what firewalls can do for network security, types of network attack. What firewall needs to control and protect and the impact of firewall in organisation network and users. A review on how network traffic can be monitored in order to prevent an unauthorized access to internal network.

2.1 Theoretical Background

Firewalls are usually the first component of network security. They separate networks in different security levels, by utilizing network access control policies. The major function of the firewall is to protect the private network from non-legitimate traffic.

Firewalls are located between the Internet and private network. They can monitor the outgoing and incoming traffic; also they can prevent the harmful traffic and attacks from Internet. They also can stop the non-legitimate outgoing traffic. If a computer from the local network is attacked by an intruder and generates non-legitimate traffic, the firewall can prevent and detect the computer. Firewall can detect such succeeded attack, so it can be recovered.

A firewall is the most effective way to connect a network to the Internet and still protect that network [1]. Firewalls create a separation between public networks (Internet) and private networks by examining the traffic according to the predefined policy, and allowing only legitimate traffic to pass between the public and private network. They help implementing a larger security policy that defines the services and access to be permitted. It is an implementation of that policy in terms of a network configuration, one or more host systems and routers, and other security measures such as advanced authentication in place of static passwords.

A firewall system can be a router, a personal computer, a host, or a collection of hosts and/or routers, set up specifically to shield a site or subnet from protocols and services that can be abused from hosts outside the subnet [2].  Firewalls must be installed at the choke points to control network traffic and implement network security policy of the organization. Firewalls achieve this by examining the all incoming and outgoing network traffic according to the predefined firewall policy. All network traffic must pass through the firewall, which ensures that only permitted traffic are allowed through [3]. Firewalls have some advantage and disadvantages they are summarized below.


• Firewalls can stop non-legitimate traffic at first point,

• Firewalls can filter protocols and services that are either not necessary or that cannot be adequately secured from exploitation [4],

• A firewall can “hide” names of internal systems and internal network schema, thereby revealing less information to outside hosts [4],

• Firewalls can concentrate extended logging of network traffic on one system.


• Firewalls utilize manually configured set of rules to differentiate legitimate traffic from non-legitimate traffic,

• Once a static policy is defined, the firewall can’t react to a network attack – nor can it initiate effective counter-measures [4],

• Firewalls only examine network packets that pass through them, do not examine network traffic between any two inside hosts,

• Most firewalls do not analyse the contents of the data packets that make up network traffic,

• Firewall policies can vary in effectiveness, depending on the expertise of the security manager and the complexity of the network environment.