Peer-to-Peer (P2P) overlay networks are a flexible way of creating decentralized services. Although resilient to external Denial of Service attacks, overlay networks can be rendered inoperable by simple flooding attacks generated from insider nodes. In this paper, we study detection and containment mechanisms against insider Denial of Service (DoS) attacks for overlay networks. To counter such attacks, we introduce novel mechanisms for protecting overlay networks that exhibit well defined properties due to their structure against non-conforming (abnormal) behavior of participating nodes. We use a lightweight distributed detection mechanism that exploits inherent structural invariants of DHTs to ferret out anomalous flow behavior. We evaluate our mechanism's ability to detect attackers using our prototype implementation on web traces from IRCache served by a DHT network. Our results show that our system can detect a simple attacker whose attack traffic deviates by as little as 5% from average traffic. We also demonstrate the resiliency of our mechanism against coordinated distributed flooding attacks that involve up to 15% of overlay nodes. In addition, we verify that our detection algorithms work well, producing a low false positive rate (< 2%) when used in a system that serves normal web traffic.
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