Alidade: IP Geolocation without Active Probing

Geolocation systems generally fall into two categories. Commercial systems provide precomputed address-to-location mappings for all IP addresses. We refer to such systems as geolocation databases. Upon presenting a geolocation database with a target IP address, a location estimate is provided immediately. Almost all systems reported in the academic literature, on the other hand, employ active measurements, issuing probes to a target after it has been specified, but before estimating the location of the target. These systems use constraints derived from the measurements to improve the accuracy of their predictions. Both approaches have their advantages. The active measurement approach may be more accurate, while the geolocation database approach is not intrusive and can answer queries quickly, even when off-line. This paper presents Alidade, a geolocation database system that makes extensive use of available network measurement data, but does not issue any probes of its own, either before or after a target is presented. Like other geolocation databases, Alidade precomputes location estimates for all of IP space. Indeed, using the available constraints, Alidade computes a joint solution for all addresses. We demonstrate that Alidade is competitive with the best commercial systems – on their own terms – using six different ground-truth data sets. Alidade also provides stronger guarantees of correctness, and each of Alidade’s predictions consists of a geographical region in addition to a representative point.