In total we detected 85 prefixes (corresponding to the 163 traceroutes) that suffered a detour that was visible from an AS which has RIPE Atlas probes. Note that some detoured prefixes were larger than /24, so we traceroute multiple IPs within it as explained in Section 6.1. The validation methodology is stated in Algorithm 1. As previous work [22] has pointed out, we found many cases where AS path seen in control plane and AS path seen in **data** plane do not match. However, these paths can still show detour if the detour origin AS and the detour destination AS are still present in the traceroute observed AS path. We call such AS paths congruent. More specifically, we consider the detoured AS path congruent only if detour origin AS and detour return AS both are present in the traceroute-observed AS path in the same order (detour origin first). For example, if an AS path 'A B C D E' in control plane changed to 'A X B C E' in **data** plane where 'B' was detour origin and 'C' was detour destination, we consider it as a congruent path. To resolve traceroute path to AS path we used CAIDA ITDK and iPlane IP to AS mappings and in cases where no match was found we use longest prefix match on the global routing table for the hop IP. Then we map the longest prefix match to the AS that originated it. Out of all the IPs we saw in 163 traceroutes, only 44 could be mapped to an AS using the IP to AS datasets. All other IPs were mapped using longest prefix match.