The detection of network communication problems in networks that have multiple end nodes, and multiple transit nodes in between. One or more of the end nodes monitors one or more flows, creates associated flow information including performance information for each flow, and then reports the flow information. A system then estimates, for each of multiple flows within the network, a likely path that network traffic takes through that network. The system might then use performance information for each of the reported flows to identify at least one candidate problem network entity that is common amongst the estimated paths of the at least the subset of the plurality of flows.