Characterizing International BGP Detours

There are currently no requirements (technical or otherwise) that BGP paths must be contained within national boundaries. Indeed, some paths experience international detours, i.e., originate in one country, cross international boundaries and return to the same country. In most cases these are sensible traffic engineering or peering decisions at ISPs that serve multiple countries. In some cases such detours may be suspicious. Characterizing international detours is useful to a number of players: (a) network engineers trying to diagnose persistent problems, (b) policy makers aiming at adhering to certain national communication policies, (c) entrepreneurs looking for opportunities to deploy new networks, or (d) privacy-conscious states trying to minimize the amount of internal communication traversing different jurisdictions. In this paper we characterize international detours in the Internet during the months of August 2014 and April 2015. To detect detours we sample BGP RIBs every 6 hours from 172 RouteViews peers spanning 22 countries; geolocate visible ASes by geolocating each BGP prefix announced by each AS; and analyze each global BGP RIB entry looking for detours. Our analysis shows more than 15K 19K unique BGP prefixes experienced a detour. A few ASes cause most detours and a small fraction of prefixes were affected the most. We observe about 2 million detours in RIBs of each month. Detours either last for a few days or persist the entire month. Out of all the detours, more than 50% 60% were transient detours that lasted for 72 hours or less.