Building Secure and Reliable Systems

Chapter 10. Mitigating Denial-of-Service Attacks

By Damian Menscher

with Vitaliy Shipitsyn and Betsy Beyer‎

Security and reliability intersect when an active adversary can trigger an outage by conducting a denial-of-service (DoS) attack. In addition to an action by an adversary, denial of service can be caused by unexpected circumstances—from a backhoe slicing through a fiber-optic cable to a malformed request crashing a server—and target any layer of the stack. Most commonly, it manifests as a sudden surge in usage. While you can apply some mitigations on top of existing systems, minimizing the effects of a DoS attack often requires careful system design. This chapter discusses some strategies for defending against DoS attacks.

Security practitioners often think about the systems they protect in terms of attack and defense. But in a typical denial-of-service attack, economics offers more helpful terms: the adversary attempts to cause the demand for a particular service to exceed the supply of that service’s capacity.¹ The end result is that the service is left with insufficient capacity to serve its legitimate users. The organization must then decide whether to incur even greater expenses by attempting to absorb the attack, or to suffer downtime (and corresponding financial losses) until the attack stops.

While some industries are more frequently targeted by DoS attacks than others, any service may be attacked in this way. DoS extortion, a financial attack in which the adversary ...