Security in computer networks and Internet have serious implications in today's dynamic work environment. It is a basic requirement because distributed computing is inherently insecure. Therefore, security mechanisms and policies must be followed and studied continually by investigating the techniques and tools for protecting assets of essential network security, which is always required and important for any organization to maintain the confidentiality, integrity and to ensure availability of data. In this context, computer networks needed to be tested and audited against any possible attacks and analyzing the existing vulnerabilities