DDoS Attack and Defense: Review of Some Traditional and Current   Techniques
  Distributed Denial of Service (DDoS) attacks exhaust victim's bandwidth or services. Traditional architecture of Internet is vulnerable to DDoS attacks and an ongoing cycle of attack & defense is observed. In this paper, different types and techniques of DDoS attacks and their countermeasures are reviewed. The significance of this paper is the coverage of many aspects of countering DDoS attacks including new research on the topic. We survey different papers describing methods of defense against DDoS attacks based on entropy variations, traffic anomaly parameters, neural networks, device level defense, botnet flux identifications and application layer DDoS defense. We also discuss some traditional methods of defense such as traceback and packet filtering techniques so that readers can identify major differences between traditional and current techniques of defense against DDoS attacks. Before the discussion on countermeasures, we mention different attack types under DDoS with traditional and advanced schemes while some information on DDoS trends in the year 2012 Quarter-1 is also provided. We identify that application layer DDoS attacks possess the ability to produce greater impact on the victim as they are driven by legitimate-like traffic making it quite difficult to identify and distinguish from legitimate requests. The need of improved defense against such attacks is therefore more demanding in research. The study conducted in this paper can be helpful for readers and researchers to recognize better techniques of defense in current times against DDoS attacks and contribute with more research on the topic in the light of future challenges identified in this paper. 
Muhammad Aamir and Mustafa Ali Zaidi
cs.CR