There is an increasing need to quickly and efficiently learn network distances, in terms of metrics such as latency or bandwidth, between Internet hosts. For example, Internet content providers often place data and server mirrors throughout the Internet to improve access latency for clients, and it is necessary to direct clients to the closest mirrors based on some distance metric in order to realize the benefit of mirrors. We suggest a scalable Internet-wide architecture, called IDMaps, which measures and disseminates distance information on the global Internet. Higher-level services can collect such distance information to build a virtual distance map of the Internet and estimate the distance between any pair of IP addresses. We present our solutions to the measurement server placement and distance map construction problems in IDMaps. We show that IDMaps can indeed provide useful distance estimations to applications such as closest-mirror selection. 1 Keywords: network service, distributed algorithms, scalability, modeling. 1

Abstract — The impact of routing policy on Internet paths is poorly understood. In theory, policy can inflate shortest-router-hop paths. To our knowledge, the extent of this inflation has not been previously examined. Using a simplified model of routing policy in the Internet, we obtain approximate indications of the impact of policy routing on Internet paths. Our findings suggest that routing policy does impact the length of Internet paths significantly. For instance, in our model of routing policy, some 20 % of Internet paths are inflated by more than five router-level hops. Keywords—Routing, Routing Policy, Policy Routing, Internet Paths I.

In our previous work, 1 we used a simplied model of routing policy in the Internet to study the impact of policy routing on Internet path-lengths. This prior work suered from two shortcomings|it was based on a single snapshot of the Internet topology, and our simplied policy model could generate AS paths that violate peering relationships. In this paper, we address these two shortcomings by re-examining our results with respect to a more recent snapshot of the Internet, and improving the policy model to avoid peering violation. We nd that our prior observations regarding the path ination due to routing policy appear to hold both across time and with respect to a more sophisticated model of routing policy. Keywords: Internet Paths, Paths, Routing Policy, Policy Routing, Path Ination 1.