SDN & OpenFlow
Traditional networking is made up of a control plane, and data plane where the control and data planes are combined each into the network elements making up the network. This creates a limitations, because the control plane, and data plane normally resides in the individual routers and switches. Any changes in the network topology (ie: links or routing/switching devices going up/down) will have to be communicated to the other network elements. This causes a propagation delay that gets longer as the network grows.
A new set of networks known as programmable networks have emerged as a solution to this problem.
The main aim of Software Defined Network (SDN) is to separate the control and data plane and transfer the network intelligence and state to the control plane. Some technologies that have exploited these concepts include Routing Control Platform (RCP), Secure Architecture for the Network Enterprise (SANE), and recently, Ethane. SDN is often related to the OpenFlow protocol. Currently, Open Networking Foundation (ONF) takes on the task of advancing SDN and standardizing OpenFlow.
Central control and simple forwarding elements
Control and management plane hardware and software dedicated resources, which resided on the switches in traditional network architecture, have now been migrated to the controller. This new architecture presents a forwarding element, which maximizes the overall resource management in the topology as the hardware processes less complex codes for forwarding the traffic.
These complex algorithms now exist in the controller, and traffic forwarding decisions are made from them, which communicates the best forwarding path for every packet to the forwarding element through a secure channel from the controller to the forwarding elements. These characteristics allow a simpler ASIC to be incorporated into the forwarding elements existing in an SDN infrastructure. This also allows the provisioning of ample resources with respect to the growth in the network size.