SPIFFY: Inducing Cost-Detectability Tradeoffs for Persistent Link-Flooding Attacks

We have recently witnessed the real life demonstration of link-flooding attacks-DDoS attacks that target the core of the Internet that can cause significant damage while remaining undetected. Because these attacks use traffic patterns that are indistinguishable from legitimate TCP-like flows, they can be persistent and cause long-term traffic disruption. Existing DDoS defenses that rely on detecting flow deviations from normal TCP traffic patterns cannot work in this case. Given the low cost of launching such attacks and their indistinguishability, we argue that any countermeasure must fundamentally tackle the root cause of the problem: either force attackers to increase their costs, or barring that, force attack traffic to become distinguishable from legitimate traffic. Our key insight is that to tackle this root cause it is sufficient to perform a rate change test, where we temporarily increase the effective bandwidth of the bottlenecked core link and observe the response. Attacks by cost-sensitive adversaries who try to fully utilize the bots' upstream bandwidth will be detected since they will be unable to demonstrably increase throughput after bandwidth expansion. Alternatively, adversaries are forced to increase costs by having to mimic legitimate clients' traffic patterns to avoid detection. We design a software-defined network (SDN) based system called SPIFFY that addresses key practical challenges in turning this high-level idea into a concrete defense mechanism, and provide a practical solution to force a tradeoff between cost vs. detectability for linkflooding attacks. We develop fast traffic-engineering algorithms to achieve effective bandwidth expansion and suggest scalable monitoring algorithms for tracking the change in traffic-source behaviors. We demonstrate the effectiveness of SPIFFY using a real SDN testbed and large-scale packet-level and flow-level simulations. Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the first-named author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.