Application - Level Distributed Denial of Service Prevention in a Replicated System

This paper presents the design and implementation of DFQ (Distributed Fair Queueing), a distributed system for defending a replicated set of HTTP servers against application-level distributed denial of service (DDoS) attacks. By using a modification of weighted fair queueing, all clients are guaranteed a fair share of the servers, no matter how many or which servers they connect to. DFQ continues to provide fair service even against malicious clients who are able to spoof additional IP addresses. It is also capable of accommodating HTTP proxies, which regularly provide many times more traffic than a single host. Such properties are desirable for package management servers and the like, whose responsiveness in the presence of flash crowds and malicious attackers is paramount to the security of the overall system. Thesis Supervisor: Hari Balakrishnan Title: Professor