Stateful anycast for distributed DDoS mitigation

Abstract

Distributed denial-of-service (DDoS) attacks can easily cripple victim hosts or networks, yet effective defenses remain elusive. Normal anycast can be used to force the diffusion of attack traffic over a group of several hosts to increase the difficulty of saturating resources at or near any one of the hosts. However, because a packet sent to the anycast group may be delivered to any member, anycast does not support protocols that require a group member to maintain state (such as TCP). This makes anycast impractical for most applications of interest. This document describes the design of Stateful Anycast, a conceptual anycast-like network service based on IP anycast. Stateful Anycast is designed to support stateful sessions without losing anycast's ability to defend against DDoS attacks. Stateful Anycast employs a set of anycasted proxies to direct packets to the proper stateholder. These proxies provide DDoS protection by dropping a session's packets upon group member request. Stateful Anycast is incrementally deployable and can scale to support many groups.