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In this paper, we investigate the problem of finding the layer-2 network topology of large, heterogeneous multisubnet Ethernet networks that may include uncooperative network nodes. We prove that finding a layer-2 network topology for a given incomplete input is an NP-hard problem, even for single subnet networks, and that deciding whether a given input defines a unique network topology is a co-NP-hard problem. We design several heuristic algorithms to find network topology, evaluate their complexity, and provide criteria for instances in which the input guarantees a unique network topology. We have implemented one of our algorithms and conducted extensive experiments on the Kent State University Computer Science network. Our experiments demonstrate that our approach is quite practical and discovers the accurate network topology of multisubnet networks whose input may not necessarily be complete.