A Survey on DDoS Defence Mechanisms

A Denial of Service (DoS) is an attempt to make a system or a group of systems unavailable to its intended users. It is mostly targeted towards web servers, mail servers, and name servers so that users have to wait for a longer duration to avail a service. Mostly DoS attacks are typically carried out to degrade the performance of a particular web server. As time is going on, DoS attack strength goes on increasing. Thus in order to mitigate DoS attacks different defence mechanisms have to be applied at different layers/levels. Dos attacks mainly affect 3 layers in the OSI model. They are network layer, transport layer and application layer. Of these 3 OSI layers, network layer has several mechanisms to mitigate DDos attacks. Mainly, Network Layer DDoS defence is of 3 types, based on the nature of the problem. They are congestion based, Anomaly based, and source based. Application layer which is very difficult to mitigate DDos attacks even under the presence of strong firewalls and Intrusion Prevention Security. Some of the Application Layer Attacks are HTTP GET DDoS Attack and HTTP POST DDoS Attack. So a robust defence mechanism should be applied to defend the application level attacks. This paper focuses on different defence mechanisms to mitigate network and application layer Dos attacks.