Distributed Denial of Service Attacks

Distributed Denial of Service (DDoS) attacks areattempts to overwhelm a computer system in order todeny access by legitimate users. They are generallyunstoppable but there is a good deal of on-goingresearch on methods to reduce their negative effects.This paper will deal with the design of a model thatsimulates such an attack. The simulation model isthen used to study possible ways to defend againstthese attacks. Three experiments are run: 1) using apriority queue to sort messages from clients based onhow many connections they have open on the server; 2)limiting the number of connections each client cancreate; and 3) having the server forcefully deletethe oldest established connection whenever itsconnection table becomes full. Results show thatmethod 1 is totally ineffective while method 2somewhat improves the overall performance of thesystem. However method 3 combined with method 2produces significantly improved performance against aDDoS attack.