Network security is an open area of applied concepts of computer sciences that has gained a lot of attention over past few years. Intrusion attacks particularly Distributed Denial of Service (DDOS) have become one of the greatest threats to the network security. To assess the network security and to deduce precautionary measures it is important to analyze how much a network is vulnerable to such intrusion attacks. The research covered in this book demonstrates a simulated flood based DDOS attack on a university network.With the help of obtained graphical results, behavior of the network under intrusion attacks is analyzed to assess vulnerability and survivability of the network. On the basis of our analysis countermeasures and possible enhancements to improve the network security against such intrusions are highlighted. We consider this book as a first step towards our future work regarding intrusion detection and prevention system design.