Software-defined networking (SDN) technology is an approach to network management that enables dynamic, programmatically efficient network configuration in order to improve network performance and monitoring, making it more like cloud computing than traditional network management. SDN is meant to address the fact that the static architecture of traditional networks is decentralized and complex while current networks require more flexibility and easy troubleshooting. SDN attempts to centralize network intelligence in one network component by disassociating the forwarding process of network packets (data plane) from the routing process (control plane). The control plane consists of one or more controllers, which are considered the brain of the SDN network where the whole intelligence is incorporated. However, the intelligent centralization has its own drawbacks when it comes to security, scalability and elasticity and this is the main issue of SDN.SDN was commonly associated with the OpenFlow protocol (for remote communication with network plane elements for the purpose of determining the path of network packets across network switches) since the latter's emergence in 2011. However, since 2012 OpenFlow for many companies is no longer an exclusive solution, they added proprietary techniques. These include Cisco Systems' Open Network Environment and Nicira's network virtualization platform.
SD-WAN applies similar technology to a wide area network (WAN).SDN technology is currently available for industrial control applications that require extremely fast failover, called Operational Technology (OT) Software Defined Networking (SDN). OT SDN technology is an approach to manage network access control and Ethernet packet delivery on environmentally hardened hardware for critical infrastructure networks. OT SDN abstracts the management of the control plane from the switches centralizing it in the flow controller and applies SDN as the underlay control plane in the switch. The legacy control plane is removed simplifying the switch while centralizing the control plane management. The common control plane standard used in OT SDN is OpenFlow making it interoperable with other SDN solutions with the difference being that OpenFlow is the only control plane in the switch and that the switch retains flows through power cycles and all flows and redundancy are proactively traffic engineered so the switches can perform the forwarding they are configured to perform with or without the flow controller online. OT SDN provides advantages for industrial networks in the form of performance, cybersecurity and situational awareness. Performance advantages are achieved through proactively traffic engineering contingencies using Fast Failover groups in OpenFlow resulting in network healing from link or switch failures in microseconds not milliseconds like spanning tree technology. Another performance advantage is that loop mitigation is done through traffic engineered path planning and not blocked ports allowing the system owner to actively use all ports. Cybersecurity advantages of OT SDN is that the switches are deny by default and flows are the rules that allow traffic to be forwarded. This provides strong network access control where packets can be inspected from layer 1 through layer 4 of the OSI model at each hop. Legacy control plane security vulnerabilities are removed since the legacy control plane no longer exists. MAC table spoofing and BPDU spoofing are no longer possible because neither exist in the OT SDN switches. Pivoting and network reconnaissance no longer work with proper flow programming as only allowed traffic is approved to be forwarded combining the physical location and path with the virtual packet filtering. Situational awareness advantages of OT SDN provide the network owner with the visibility to what devices are on their network and what conversations can and are happening and who those conversations can happen between. OT SDN network technology allows Ethernet networks to meet the demanding communication message exchange requirements of measurement and control for critical infrastructure and simply provides the system owner control over what devices can connect to the network, where those devices can connect, and what conversations each device can have.
Research of SDN continues as many emulators are being developed for research purposes, like vSDNEmul, EstiNet, Mininet etc.