We propose a novel measurement technique for network delay tomography that infers network-internal queueing delay using network routers as measurement nodes. In contrast to existing tomography techniques, the proposed technique does not require any additional infrastructure support, and can thus be directly applied to the analysis of network performance and the study of the Internet. We study the implications of using network routers as measurement nodes, showing the feasibility and constraints of our approach using extensive network measurements. We also report on the use of our method for the study of Internet paths with respect to the existence of single or multiple bottlenecks. Our preliminary results show the existence of such paths may not be negligible. This result has potential implications on the evaluation and fairness of congestion control mechanisms.