Strategic resource management decisions in computer networks

Resource management problems play an important role in technology and economy. In general, resource management tries to use an enterprise’s resources as efficiently as possible to maximize a (potentially financial) benefit. This thesis addresses two specific resource management problems in computer networks. Resource Management during Denial-of-Service Attacks During a denial-of-service (DoS) attack, an attacker exhausts the resources of one or multiple Internet services by sending large amounts of requests, making the service unavailable. Besides filtering of attack traffic, overprovisioning is a common defense against this attack: The victim tries to have enough resources available to stay operational despite the DoS attack. Traditional resource management techniques like load balancing are not sufficient here, as an attacker does not just create load, but acts strategically to maximize damage to the victim. Modern computer networks are complex meshes of services that depend on each other. Back end services like DNS or databases are often required to provide the front end services that users are interested in. Such dependencies may create capacity bottlenecks that can be exploited by a DoS attacker to cause more damage with less effort. In this thesis, we develop methods to uncover such vulnerabilities and to help fix them. To do this, we investigate game-theoretic models of the interaction between attacker and defender. We designed and implemented a network simulator to quickly simulate denial-of-service attacks and use it together with optimization algorithms to find good strategies for attacker and defender. We further show that virtualization of services gives the defender an advantage, as he is able to re-configure his network during an attack. Since the attacker can observe the new network configuration only indirectly, he needs time to adapt his attack strategy. We also investigate a novel defense mechanism against denial-of-service attacks based on a layer of proxy servers between the clients and the server. This defense can be set up quickly even after the attack has started. Further we present a feasibility study of a worm, which performs denial-of-service attacks against cellular mobile networks. We show that overloading individual cells with user data is a serious threat if the attacker coordinates it correctly. A possible countermeasure, is a resource management system that moves users to less-loaded cells. Resource Management in mobile Networks Mobile Networks today consist of different access technologies. Besides traditional cellular networks like GSM and UMTS, modern mobile networks often incorporate