Software Defined Networking (SDN) is an emerging paradigm based on the separation between the control plane and the data plane. The knowledge of the network topology by the controller is essential to allow the implementation of efficient solutions of network management and network resource utilization. Most of the OpenFlow SDN controllers include a mechanism to discover the network nodes (router and switches) and the links between them. However, they do not consider other important elements of the networks: the hosts. In this paper we propose a host discovery mechanism to improve the topology discovery solutions in SDN networks. The proposed mechanism, that has been coded as a software module in Ryu SDN controller, allows the detection and tracking of hosts even when they don’t generate traffic. The implemented software module has been tested in emulated SDN networks and in real scenarios using ONetSwitch, a real programmable SDN platform.