Through the Looking Glass: Analyzing Geolocation Providers Using Looking Glasses and Active Measurements

Looking Glass servers (LGs) allow users and network operators to debug issues or measure performance to/from arbitrary, external IP addresses, making LGs a valuable tool in a variety of analyses. To assess the reliability of LGs as an independent and free set of vantage points, we perform an analysis of 4487 LG servers across 144 countries. We analyze LGs by comparing them to six different geolocation databases from four providers, and by conducting active measurements on LGs. In our RTT measurements we find 9 of 18 LG providers have at least one server with an RTT-disconfirmed location. We also find substantial differences between geolocation databases’ ability to locate LGs, with IPinfo showing the closest distance to LGs.