The main issue related to Software-Defined Network emulators is how to replicate real behavior in experiments. Mininet and others SDN emulators have an architecture that limits both the scope of experiments and the fidelity of networking tests. Consequently, the serialization, contention, and load of background processes may produce delays that compromise the operation of events such as transmitting a packet or completing a computation, possibly invalidating the performance evaluation of a network emulation. To address these problems, this paper presents vSDNEmul, a network emulator based on Docker container virtualization. Different from Mininet, vSDNEmul isolates each node in a container and interconnects the nodes through virtual or tunnel links. By using containers, vSDNEmul allows autonomous and flexible creation of independent network elements, resulting in more realistic emulations. This paper reports performance evaluations comparing vSDNEmul and Mininet. The results obtained with the vSDNEmul emulator are more realistic and present higher accuracy.