  We present CommunityWatch, an open-source system that enables timely and
accurate detection of BGP routing anomalies. CommunityWatch leverages meta-data
encoded by AS operators on their advertised routes through the BGP Communities
attribute. The BGP Communities values lack standardized semantics, offering the
flexibility to attach a wide range of information, including AS relationships,
location data, and route redistribution policies. Therefore, parsing and
correlating Community values and their dynamics enables the detection and
tracking of a variety of routing anomalies. We exhibit the efficacy of
CommunityWatch through the detection of three different types of anomalies:
infrastructure outages, route leaks, and traffic blackholing.
