Issues with inferring Internet topological attributes

A number of recent studies are based on data collected from routing tables of inter-domain routers utilizing Border Gateway Protocol (BGP) and tools, such as traceroute, to probe end-to-end paths. The goal is to infer Internet topological properties. However, as more data is collected, it becomes obvious that data intended to represent the same properties, if gathered at different points within the network, can depict significantly different characteristics. While systematic data collection from a number of network vantage points can reduce certain ambiguities, thus far, no methods have been reported for fully resolving these issues. The goal of our study was to quantify the effect these anomalies have on key Internet structural attributes. We report on our analysis of over 290,000 measurements from globally distributed sites. We contrast results obtained from router-level measurements with those obtained from BGP routing tables, and offer insights as to why certain inferred properties differ. We demonstrate that the effect on some attributes, such as the average path length and the AS degree distribution can be minimized through careful data collection techniques. We also illustrate how using this same data to model other attributes, such as the actual forwarding path between a pair of nodes, or the level of AS path asymmetry, can produce substantially misleading results.