Following the Data Trail: An Analysis of IXP Dependencies

Internet exchange points (IXPs) play a vital role in the modern Internet. Envisioned as a means to connect physically close networks, they have grown into large hubs connecting networks from all over the world, either directly or via remote peering. It is therefore important to understand the real footprint of an IXP to quantify the extent to which problems (e.g., outages) at an IXP can impact the surrounding Internet topology. An IXP footprint computed only from its list of members as given by PeeringDB, or the IXP’s website, is usually depicting an incomplete view of the IXP as it misses downstream networks whose traffic may transit via an IXP although they are not directly peering there. In this paper we propose a robust approach that uncovers this dependency using traceroute data from two large measurement platforms. Our approach converts traceroutes to paths that include both autonomous systems (ASes) and IXPs and computes AS Hegemony to infer their inter-dependencies. This technique discovers thousands of dependent networks not directly connected to IXPs and emphasizes the role of IXPs in the Internet topology. We also look at the geolocation of members and dependents and find that only \({3}{\%}\) of IXPs with dependents are entirely local: all members and dependents are in the same country as the IXP. Another \({52}{\%}\) connect international members, but only have domestic dependents.