Software Defined Networking (SDN), often referred to as a revolutionary new idea in computer networking, promises to dramatically simplify network control, management, and enable innovation through network programmability.

The separation of the forwarding hardware from the control logic allows easier deployment of new protocols and applications, straightforward network visualization and management, and consolidation of various middle boxes into software control. Instead of enforcing policies and running protocols on a convolution of scattered devices, the network is reduced to simple forwarding hardware and the decision-making network controller(s). The forwarding hardware consists of the following:

1. A flow table containing flow entries consisting of match rules and actions that take on active flows.

2. A transport layer protocol that securely communicates with a controller about new entries that are not currently in the flow table.

While OpenFlow has received a considerable amount of industry attention, it is worth mentioning that the idea of programmable networks and decoupled control plane (control logic) from data plane has been around for many years. The Open Signaling Working Group (OPENSIG) initiated a series of workshops in 1995 to make ATM, Internet, and mobile networks more open, extensible, and programmable. Motivated by these ideas, an Internet Engineering Task Force (IETF) working group came up with General Switch Management Protocol (GSMP), Network initiative proposed the idea of a network infrastructure that would be programmable for customized services. However, Active Network never gathered critical mass, mainly due to practical security and performance concerns.