The recent Denial of Service (DoS) attacks against high-profile web sites shows how overwhelming DoS attacks are and how unprotected the Internet is under such attacks. The authors present a survey of the current proposed mitigations against Denial of Service (DoS) attacks that give a promising approach to the field. Weaknesses of the available methods are also presented which result to the fact that no unified method has been adopted yet. They also make a discussion about the future trends in DoS defense. In fact DoS is technical attack therefore can be handled only by knowing its technical aspects.