科研之友
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摘要
Although traceroute has the potential to discover AS links that are invisible to existing BGP monitors, it is well known that the common approach for mapping router IP addresses to AS numbers based on BGP routing tables is highly error-prone. We develop a systematic framework to quantify the potential errors of traceroute measurement in AS-level topology inference. In comparing traceroute-derived AS paths with BGP AS paths, we take a novel approach to identifying mismatched path segments and then inferring the causes of these mismatches through a set of tests. Our results show that about 60% of mismatches are due to routers using IP addresses belonging to peering neighbors. This result helps settle a debate in previous works regarding the major cause of errors in traceroute measurement. With the approximate ground truth of the ASes with BGP monitors inside, we identify the inaccuracy of publicly available traceroute-derived topology datasets and find that between 8% and 42% of AS adjacencies on the monitored ASes are false. With a new method to characterize AS links, we show that the derived (false) links between Tier-1/large ISPs and their customers' customers appear more frequently than real links do.
