Abstract”In this paper, we consider the problem of detecting whether a compromised router is maliciously manipulating its stream of
packets. In particular, we are concerned with a simple yet effective attack in which a router selectively drops packets destined for some
victim. Unfortunately, it is quite challenging to attribute a missing packet to a malicious action because normal network congestion can
produce the same effect. Modern networks routinely drop packets when the load temporarily exceeds their buffering capacities.
Previous detection protocols have tried to address this problem with a user-defined threshold: too many dropped packets imply
malicious intent. However, this heuristic is fundamentally unsound; setting this threshold is, at best, an art and will certainly create
unnecessary false positives or mask highly focused attacks. We have designed, developed, and implemented a compromised router
detection protocol that dynamically infers, based on measured traffic rates and buffer sizes, the number of congestive packet losses
that will occur. Once the ambiguity from congestion is removed, subsequent packet losses can be attributed to malicious actions. We
have tested our protocol in Emulab and have studied its effectiveness in differentiating attacks from legitimate network behavior.
mahadev