Software-defined networking (SDN) may be the technology du jour, but as of yet it is largely conceptual -- and those concepts vary depending on the approach. Vendors talk about their own SDN architectures, OpenFlow, SDN APIs, and overlay networks either as if they are interchangeable, or without ever mentioning the other options. It's no wonder that SDN leaves many folks in IT with no grasp of the "definition" at all.
The basis of SDN is virtualization, which in its most simplistic form allows software to run separately from the underlying hardware. Virtualization has made cloud computing possible and now allows datacenters to dynamically provision IT resources exactly where they are needed, on the fly. To keep up with the speed and complexity of all this split-second processing, the network must also adapt, becoming more flexible and automatically responsive. We can apply the idea of virtualization to the network as well, separating the function of traffic control from the network hardware, resulting in SDN.
Whether out of a need for self-preservation or a desire to improve technology, the networking industry is embracing SDN with surprising enthusiasm. Legacy networks have serious limitations and old methods that simply will no longer work. As virtualization, cloud, and mobility create more complex environments, networks must be able to adapt in terms of security, scalability, and manageability. Most enterprise networks, however, rely on fixed boxes and appliances requiring a great deal of manual administration. Changing or expanding these networks for new capabilities, applications, or users requires reconfiguration that is time consuming and expensive.
Software-defined networks take a lesson from server virtualization and introduce an abstraction layer separating network intelligence and configuration from physical connections and hardware. In this way, SDN offers programmatic control over both physical and virtual network devices that can dynamically respond to changing network conditions using OpenFlow or some other programmable and controllable packet/flow processing protocol.
There are several approaches to SDN, but the most common components and concepts are covered in the following slides. Though the technology is very much in the midst of its development, vendors and industry organizations are working to make the technology open and flexible while adhering to existing Internet standards. At its core, SDN promises to enable network technology innovation and versatility while reducing complexity and administrative overhead.