Evaluation of distributed applications and network protocols is a difficult task, which can hardly be done by means of real world experiments. Also simulation cannot always be a good approach, because the test subject has to be adapted. Emulation as a third approach, which tries to combine the benefits of both real world experiments and simulation. With increasing hardware performance, emulation based on virtual machines, becomes feasible. Therefore, this case study evaluates the suitability of virtual machine implementations with different designs for use in computer network emulation. A comparison is drawn to an emulation approach based on virtual routing. It is shown that virtual machines are suitable for network emulation, however there are huge performance differences between the different implementations, and huge hardware requirements are needed compared to other computer network emulation approaches.