A measurement study on BGP AS path looping (BAPL) behavior

As a path vector protocol, Border Gateway Protocol (BGP) messages contain the entire Autonomous System (AS) path to each destination for breaking arbitrary long AS path loops. However, after observing the global routing data from RouteViews, we find that BGP AS path looping (BAPL) behavior does occur and in fact can lead to multi-AS forwarding loops in both IPv4 and IPv6. The number and ratio of BAPLs in IPv4 and IPv6 for 1456 days on a daily basis are analyzed. Moreover, the distribution of BAPL duration and loop length in IPv4 and IPv6 are also studied. Some possible explanations for BAPLs are discussed in this paper. Private AS number leaking has contributed to 1.76% of BAPLs in IPv4 and 0.00027% in IPv6, and at least 2.85% of BAPLs in IPv4 were attributed to faulty configurations and malicious attacks. Valid explanations, including multinational companies, preventing particular AS from accepting routes, can also lead to BAPLs.