Flow allows the link of several controllers to a switch, which would permit backup controllers to get over in the event of a failure. Onix and HyperFlow get the thought further by attempting to keep a logically centralized, but physically circulated control plane. This decreases the lookup overhead by enabling message with local controllers, while still allowing applications to be written by means of a simplified central vision of the system. The possible major downside of this approach is maintaining the reliable state in the overall distributed system. This may cause Net Apps, SO as to believe they have an correct outlook of the network, to proceed incorrectly due to inconsistency in the worldwide network condition. Recalling the operating system similarity, an OpenFlow controller acts as a system operating system and be supposed to implement at least two interfaces: a southbound interface SO as to allows OpenFlow switches to converse with the controller, and a northbound interface that presents a programmable application programming interface (API) to system control and management applications (that is, Net Apps). Existing Implementations in Controllers Currently, there are dissimilar OpenFlow (and SDN) controller implementations, Open Source Resources, as part of existing open source projects. Table 3 shows the list of controllers in SDN. POX CONTROLLER The major component of a Software Defined Networks is the SDN controller, called a network operating system. The controller is what defines the environment of the SDN paradigm. It is the in charge component for intent communication with all programmable basics of the network, providing a united view of the system. POX Downloaded 4/15/2022 9:44:49 AM Nova Southeastern University IP Address: 137.52.76.29 SDN Controller Table 3. List of controllers Controller Implementation Developer Python Nicira Python/C++ Nicira Kulcloud Maestro Rice university Trema Ruby/C Beacon Standford Jaxon Independent developers Helios Floodlight BigSwitch Nicira Python NTT, OSRG group 