work administrators to programmatically initialize, manage, alter, and direct network behavior dynamically through open interfaces and abstraction of lower-level functionality. SDN controller is an application in software-defined networking (SDN) SO as to manages run control to permit clever networking. SDN controllers are based on protocols, such as OpenFlow, that permit servers to inform switches where to send packets. So controller is the a large amount important thing in Software Defined Networking. The fifth chapter discusses the working of different types of controllers and their working. The chapter is to gloss over the various types and functionalities of controllers present in the field of Software Defined Networking. It is responsible for providing a bridge between various application interfaces. It enables smart networking Downloaded 4/15/2022 9:44:49 AM Nova Southeastern University IP Address:137.52.76.29 Preface and is solely responsible for having an authority over the network. It takes input from one API, process it and return output for the high level interface or API. They instruct the switch as to what functions to perform and can be of two types either pure or hybrid. The controller at the central layer performs all the functions of the "evergreen" existing switches. The data plane of the router is solely the foreground for the switch to apply all its powers. While in hybrid switch Software defined networking and existing technologies work hand in hand. An administrator can build up the SDN tools to manage the traffic whereas the existing network protocols progressively move the various incoming packets onto the network. This engenders hybrid network. Here the existing and SDN technologies or switches, work under the similar conditions. The sixth chapter presents the practical approach of software defined network with Cisco. This chapter focusses on SDN Practical approach with Cisco Controllers APIC, APIC-EM and the application programming Interfaces with real world benefits and challenges. The