Towards Understanding City-Level Routing using BGP Location Communities

BGP communities are widely used by operators to encode routing metadata for traffic engineering, policy enforcement, and operational debugging. However, ~90% of observed communities lack public documentation, limiting their utility for research and operational analysis. Among these, city-level communities offer valuable geographic insight into routing behavior, yet remain largely untapped. In this paper, we develop a scalable method to infer the geographic meaning of undocumented city communities using BGP data. We validate our approach against a ground truth dataset covering 1,482 city communities and through operator feedback. Applied to data from May 2025, our algorithm infers the locations of 80% of city communities with a precision of 70~km or better. We publish all code and datasets to support reproducibility and further research.