Network security parameters and their optimization

Security in computer networks and Internet comprise serious issues in today's dynamic work environment. Besides increasing new vulnerabilities and exploits, sometime even a fully patched system or network have security gaps,therefore network and system administrators should focus on the best setting for decreasing vulnerabilities in the network. In order to protect single users, companies, customers and business partners from the attacks of hackers, it is needed to think just like a hacker.It is also essential to decrease and stop loopholes of network and set Operating System and third party devices in a best optimized situation. In order to find these weaknesses penetration testsshould be used. Due to the daily development of the information technology, a certain vulnerability or attack refuses to workafter a certain time but the knowledge about the software and third party devices can help identifying similar behaviors in the future. In this thesis, it is aimed to give basic information to network administrators about network security and common network vulnerabilities to identify and explain a suitable penetration testing methodology. Besides illustrate some free and open source network surveying tools, port scanners, vulnerability scanners to simulate possible attacks that network and system administrators can use against their network or system during a penetration test were also given. For this purpose, the network scanning and penetrating tools were analyzed and Nmap, Nessus and Metasploit open source software are selected. The testbedused in this thesis consists of one firewall andtwo systems representing two hosts which are located in two different networks.The experiments were carried out on these networks and found that, there were some vulnerabilities existingin the testbed.