Detecting Unusually-Routed ASes: Methods and Applications.

ABSTRACTThe routes used in the Internet's interdomain routing system are a rich information source that could be exploited to answer a wide range of questions. However, analyzing routes is difficult, because the fundamental object of study is a set of paths. In this paper we present new analysis tools -- metrics and methods -- for analyzing AS paths, and apply them to study interdomain routing in the Internet over a recent 13-year period. Our goal is to develop a quantitative understanding of changes in Internet routing at the micro level (of individual ASes) as well as at the macro level (of the set of all ASes). To that end we equip an existing metri (Routing State Distance) with a new set of tools for identifying and characterizing unusually-routed ASes. At the micro level, we use our tools to identify clusters of ASes that have the most unusual routing at each time (interestingly, such clusters often correspond to sets of jointly-owned ASes). We also show that analysis of individual ASes can expose busis and engineering strategies of the organizations owning the ASes. These strategies are often related to content delivery or service replication. At the macro level, we show that ASes with the most unusual routing define discernible and interpretable phases of the Internet's evolution. Furthermore, we show that our tools can be used to provide a quantitative measure of the "flattening" of the Internet.