The SDN switch (for instance, an OpenFlow switch), the SDN controller, and the interfaces are present in the controller for communication with forwarding devices, generally southbound interface (OpenFlow), and northbound interface (the network application interface), which are the fundamental building blocks of an SDN deployment. Switches in an SDN are often represented as basic forwarding hardware accessible via an open interface, as the control logic and algorithms are offloaded to a controller. OpenFlow switches come in two varieties: pure (OpenFlow-only) and hybrid (OpenFlow-enabled).
Pure OpenFlow switches have no legacy features or onboard control and completely rely on a controller for forwarding decisions. Hybrid switches support OpenFlow in addition to traditional operation and protocols. Most commercial switches available today are hybrids. An OpenFlow switch consists of a flow table, which performs packet lookup and forwarding. Each flow table...