Internet Service Providers (ISPs) can exploit path diversity to balance load and improve robustness. Unfortunately, it is difficult to evaluate the potential impact of these approaches without routing and topological data, which are confidential. In this paper, we characterize path diversity in the real Sprint network. We then characterize path diversity in ISP topologies inferred using the Rocketfuel tool. Comparing the real Sprint topology to the one inferred by Rocketfuel, we find that the Rocketfuel topology has significantly higher apparent path diversity. We evaluate heuristics that improve the accuracy of the inferred Rocketfuel topologies. Finally, we discuss limitations of active measurements techniques to capture topological properties such as path diversity. Categories and Subject Descriptors C.2.1 [Computer Communications and Networks]: Network Architecture and Design—network topology General Terms Measurement Keywords Path diversity, Internet topology