Abstract-Achieving cost-effective systems for network performance monitoring has been the subject of many research works over the last few years. Most of them adopt a two-step approach. The first step assigns optimal locations to monitoring devices, whereas the second step selects a minimal set of paths to be monitored. However, such an approach does not consider the trade-off between the optimization objectives of each step, and hence may lead to sub-optimal usage of network resources and biased measurements. In this paper, we propose to evaluate and reduce this tradeoff. Toward this end, we come up with two ILP formulations for a novel monitoring cost model. The aim is to jointly minimize the monitor location cost and the anomaly detection cost, thereby obtaining a monitoring solution that minimizes the total monitoring cost. Our formulations apply for both active and passive monitoring architectures. We show that the problem is NP-hard by mapping it to the uncapacitated facility location problem. Simulation results illustrate the interplay between the optimization objectives and evaluate the quality of the obtained monitoring solution.