Recently many prominent web sites face so called Distributed Denial of Service Attacks (DDoS). While former security threats could be faced by a tight security policy and active measures like using rewalls, vendor patches etc. these DDoS are new in suchway that there is no completely satisfying protection yet. In this paper we categorize different forms of attacks and give an overview over the most common DDoS tools. Furthermore we present a solution based on Class Based Routing mechanisms in the Linux kernel that will prevent the most severe impacts of DDoS on clusters of web servers with a prepended load balancing server. The goal is to keep the web servers under attack responding to the normal client requests. Some performance tests and a comparison to other approaches conclude our paper.