Software-defined networking (SDN) is a software layer which allows administrators to control the network devices through a software interface instead of manual configuration of the hardware.
Network devices such as routers are separated into two planes. The control plane lists which route and physical interface connection should be used to forward the data packets.
The forwarding plane forwards the packets between incoming and outgoing connections, using data from the control plane.
Through SDN the two planes are decoupled and the control plane is controlled by software. This means administrators do not need to execute all command and control rules on the hardware itself.
Traffic can be controlled centrally from a network console, changing traffic rules on a case-by-case basis if necessary.
Big networking companies such as Cisco, IBM, Juniper Networks, Citrix and Dell all have SDN products.
Advantages include vendor neutrality and simplification of connections between network devices leading to greater agility.
