This paper presents a comprehensive study on the performance of common MANET (mobile ad hoc network) routing protocols under realistic network scenarios. The routing protocols used in this study include AODV, DSR, OLSR, OSPFv2 and ZRP, which comprise a good mix of reactive, proactive and hybrid protocols. The paper evaluates these protocols under simulation scenarios based on an actual exercise carried out under the DARPA FCS Communications Program. Mobility of the nodes was simulated using GPS logs from the field exercise. Traffic is simulated using a model of the traffic generation tool that drove traffic in the live exercise, and reads the same script files. The simulation results produced by QualNet are first validated against the corresponding measurements taken from the exercise, and several network configuration parameters are then varied to examine the performance of these protocols under "what-if" scenarios. This simulation study together with its post analysis show...