Software Defined Networking (in short SDN, which is also an acronym for Software Defined Network), has emerged as a response to the limitations and complexities of traditional network architectures. At the heart of SDN lies the idea to consolidate the control over network devices into a logically centralized (software) controller separated from the data plane. The separation of the control plane and the data plane is realized via an open programming interface between the data plane switches and the SDN controller. The decoupling allows the control plane to evolve independently of the data plane, which enables faster innovation since software often exceeds hardware in innovation speed. Furthermore, logical centralization has the potential to simplify network operation and management by providing a single focal point where the consequences of management actions can be assessed, and possibly rejected if they would lead to some violation of operational constraints. OpenFlow, the standard SDN protocol today, is based on a simple match-action paradigm which results in great flexibilities, e.g., in terms of traffic engineering, definition of flows, as well as in-band network control functionalities.

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