ted by different vendors won't all be compared. But the discussion holds in stock a great fathomed discussion about various popular SDN controllers DOI: 10.4018/978-1-5225-3640-6.ch005 Copyright © 2018, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Downloaded: 4/15/2022 9:44:49 AM Nova Southeastern University IP Address: 137.52.76.29 The Heart and Brain of SDN like NOX, POX, Flood Light, RYU etc. A closer look would be given to the free side of the market i.e. open source side. Being the vortex of the software defined architecture; the controllers belonging to this category have also developed with a period of time. BACKGROUND The rise of this concept was given when the data centers saw that the network devices had to reconfigure. This was a tedious task as they had to manually do it and keep any eye on every device if something goes wrong. The evolution of networks overtime gave birth to software defined networking and network virtualization. The control and data plane of the router are separated and instead of control plane being in charge a controller agent is in charge there in SDN architecture. The controller agents communicate with the SDN controller which in return provide dynamic path allocation to devices depending on the network load. Giving the past, present and future scenarios it is time to focus on the agenda of the chapter. The SDN controllers which form the key component of this macrocosm. DEFINITION A SDN controller is software's piece in software-defined networking (SDN) that controls or manages the flow control of the network to initiate smart networking. SDN controllers are prepared to function on various protocols, most popular being Open Flow, that allows servers to tell, switches where to send packets. Before diving into the basics of what a SDN controller is, what their types are and how do they all differ from each other, the very miniscule thing to look at is what it comes to our mind whenever we hear controller. 