ABSTRACT On the way to obtaining accurate AS-level traceroute paths, lots of efforts have focused on the improvement of the original IP-to-AS mapping table which was extracted from BGP routing tables. One of those efforts is called pair matching which refines the original mapping table by maximizing the number of matched pairs of traceroute and BGP AS paths from the same AS to the same destination. However, in the existing pair-matching-based method, the granularity for mapping is prefix, i.e. that the IP addresses in the same /24 prefix always belong to the same AS or set of ASes, which may yield ambiguity and does not hold in some cases. In this paper, we revisit the IP-to-AS mapping with IP-address granularity by allowing IP addresses in the same prefix to be mapped to different ASes