Controller redundancy

In the centralized controlled environment, such as OpenFlow, we need to be prepared for fault tolerance on the controller. This is generally the first thing we need to consider in our deployment. In production network, we need to plan for controller failure or any communication failure between controller and the switch. Prior to OpenFlow 1.3, the orchestration of controllers needed to be done via a third party software or between controllers themselves for negotiating the primary controller. Starting in OpenFlow 1.3, this can be done via the OFPT_ROLE messages between the controller and the switch. In OpenFlow 1.3, the switch can connect to multiple controllers and the controller's role can be equal, master, or slave. In equal role, it is just as if the switch has two masters, each having full access to the switch. In a slave role, the controller has only read access to the switch, does not receive asynchronous messages, and is denied any flow-mod, packet-out, or other...