2.0 CHAPTER TWO 2.1 INTRODUCTION The ever increasing need for information technology as a result of globalisation has brought about the need for an application of a better network security system. It is without a doubt that the rate at which computer networks are expanding in this modern time to accommodate higher bandwidth, unique storage demand, and increase number of users can not be over emphasised. As this demand grows on daily bases, so also, are the threats associated with it. Some of which are, virus attacks, worm attacks, denial of services or distributed denial of service attack etc. Having this in mind then call for swift security measures to address these threats in order to protect data reliability, integrity, availability and other needed network resources across the network. Generally, network security can simply be described as a way of protecting the integrity of a network by making sure authorised access or threats of any form are restricted from accessing valuable information. As network architecture begins to expand, tackling the issue of security is becomes more and more complex to handle, therefore keeping network administrators on their toes to guard against any possible attacks that occurs on daily basis. Some of the malicious attacks are viruses and worm attacks, denial of service attacks, IP spoofing, cracking password, Domain Name Server (DNS) poisoning etc. As an effort to combat these threats, many security elements have been designed to tackle these attacks on the network. Some of which includes, firewall, Virtual Private Network (VPN), Encryption and Decryption, Cryptography, Internet Protocol Security (IPSec), Data Encryption Standard (3DES), Demilitarised Zone, (DMZ), Secure Shell Layer (SSL) etc. This chapter starts by briefly discussing Internet Protocol (IP), Transmission Control Protocol (TCP), User datagram Protocol (UDP), Internet Control Message Protocol (ICMP), then discussed the Open system interconnection (OSI) model and the protocols that operate at each layer of the model, network security elements, followed by the background of firewall, types and features of firewalls and lastly, network security tools. 2.2 A BRIEF DESCRIPTION OF TCP, IP, UDP AND ICMP 2.2.1 DEFINITION Going by the tremendous achievement of the World Wide Web (internet), a global communication standard with the aim of building interconnection of networks over heterogeneous network is known as the TCP/IP protocol suite was designed (Dunkels 2003; Global Knowledge 2007; Parziale et al 2006). The TCP/IP protocol suite is the core rule used for applications transfer such as File transfers, E-Mail traffics, web pages transfer between hosts across the heterogeneous networks (Dunkels 2003; Parziale et al 2006). Therefore, it becomes necessary for a network administrator to have a good understanding of TCP/IP when configuring firewalls, as most of the policies are set to protect the internal network from possible attacks that uses the TCP/IP protocols for communication (Noonan and Dobrawsky 2006). Many incidents of network attacks are as a result of improper configuration and poor implementation TCP/IP protocols, services and applications. TCP/IP make use of protocols such as TCP, UDP, IP, ICMP etc to define rules of how communication over the network takes place (Noonan and Dobrawsky 2006).
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