In the past few years, there has been intense interest in designing and studying peer-to-peer networks. Many initial measurement studies on current deployed peer-to-peer networks attempted to understand their performance [10, 11, 12]. However, the large size and complex nature of these networks make it difficult to analyze their properties. Simulation of these peer-to-peer networks enables a methodical evaluation and analysis of their performance. However, to our knowledge, there is no tool for simulating different peer-to-peer network protocols for a comparative study. We present p-sim: a tool that can simulate peer-to-peer networks on top of representative Internet topologies. p-sim has several capabilities to provide an accurate model of real-world peer-to-peer networks. p-sim can scale to thousands of nodes and is extensible to simulate new peer-to-peer network protocols. In this paper, we discuss the capabilities of p-sim, its user-interface and two case-studies.