This article presents a comparative study of three hybrid network simulators: OPNET’s Modeler and ns-2, as well as NCTUns. In order to fulfill this, the simulated results were compared with the results obtained from a real network testbed using a packet by packet analysis methodology. Using a generic network based in an experimental network and modeled in the three simulators, the experimental comparison consisted in introducing data traffic in six different scenarios, combining traffic patterns of Constant Bit Rate (CBR) and a File Transfer Protocol session (FTP). The first objective is to corraborate the precision of the used models in the simulation to create this traffic patterns. Second, to test the network response to these types of traffic, all these by using the same packet by packet analysis methodology. The results obtained from the simulators were compared against the results obtained from the testbed network. The results obtained in this study showed that ns-2 presents good results in the simulation of CBR traffic, while the Modeler from OPNET presents an outstanding traffic simulation in terms of the FTP traffic. Nevertheless, some problems were detected in the three simulators, but NCTUns was the one that presented the most number of errors and problems in the overall results. These types of studies at the packet by packet level are important to validate the models used in the simulations that are based in components and applications used in grand scale simulations.