Early detection of network troubles such as link down is important in the management of communication networks. However, it is difficult to correctly locate the failed network device since the networks are time-evolving, redundant, and not directly-observable. In this paper we focus on a detection algorithm that allows for detecting the change in a given network structure (topology) and for locating the failed link. After sending a sufficient number of test packets (probes) among multiple pairs of end nodes, we evaluate the likelihood of failure on each of the existing links. Then we use maximum likelihood estimation to detect failure and to infer the most suspicious link. Simulation experiments demonstrate that our method can identify the location of a failed link with good accuracy.