SDN has changed the way of thinking about networks. SDN networks are flexible, scalable and easily manageable. Application that runs on the management plane actually utilize the network efficiency, So application developed should be capable of handling the controllers functionality. Each of the application that runs should be free from viruses, so that it does not affect the controller. Also we need to increase the level of security in all layers of the SDN architecture. SDN is growing faster and faster and it has reached the platform where we can also apply other fields concepts. Now SDN researcher are looking for the overcome the existing drawback. So that it can even support heterogeneous networks in a very smooth and flexible way.