A major recent development in computer networking is the emergence of Software Defined Networking (SDN), whose goal is to provide a centralized, programmable control plane that is decoupled from the distributed data planes on individual network devices. In particular, the development of OpenFlow has demonstrated many potential benefits of SDN, and multiple vendors have started to offer commercial switches supporting the OpenFlow standard. Researchers have also made progress on SDN components including SDN controllers, switches, programming interfaces, verification and debugger tools, and SDN applications in data center network, campus network, routing, and traffic engineering. Despite the progress, many important questions regarding SDN still remain, especially in longer term issues around SDN thermal foundation, programmability and control logic, formal methods and protocol engineering, abstraction and view, network operating system, etc.