The Open Networking Foundation (ONF), a user-led organization dedicated to promotion and adoption of software-defined networking (SDN), manages the OpenFlow standard. ONF defines OpenFlow as the first standard communications interface defined between the control and forwarding layers of an SDN architecture. OpenFlow allows direct access to and manipulation of the forwarding plane of network devices such as switches and routers, both physical and virtual (hypervisor-based). It is the absence of an open interface to the forwarding plane that has led to the characterization of today’s networking devices as monolithic, closed, and mainframe-like. A protocol like OpenFlow is needed to move network control out of proprietary network switches and into control software that's open source and locally managed.
In simpler terms, OpenFlow allows the path of network packets through the network of switches to be determined by software running on multiple routers (minimum two of them — primary and secondary — has a role of observers). This separation of the control from the forwarding allows for more sophisticated traffic management than is feasible using access control lists (ACLs) and routing protocols. Its inventors consider OpenFlow an enabler of SDN.
A number of network switch and router vendors have announced intent to support or are shipping supported switches for OpenFlow, including Alcatel-Lucent, Big Switch Networks, Brocade Communications, Arista Networks,NoviFlow, Cisco, Dell Force10, Extreme Networks, IBM, Juniper Networks, Digisol, Larch Networks, Hewlett-Packard, NEC, and MikroTik. Some network control plane implementations use the protocol to manage the network forwarding elements. OpenFlow is mainly used between the switch and controller on a secure channel. A fairly comprehensive list of OpenFlow-related products may be found on the ONF website and the SDNCentral website.
Version 1.1 of the OpenFlow protocol was released on February 28, 2011, and new development of the standard was managed by the Open Networking Foundation (ONF). In December 2011, the ONF board approved OpenFlow version 1.2 and published it in February 2012. The current version of OpenFlow is 1.4.
Indiana University in May 2011 launched a SDN Interoperability Lab in conjunction with the Open Networking Foundation to test how well different vendors' Software-Defined Networking and OpenFlow products work together.
In February 2012, Big Switch Networks released Project Floodlight, an Apache-licensed open-source software OpenFlow Controller, and announced its OpenFlow-based SDN Suite in November of that year, which contains a commercial controller, and virtual switching and tap monitoring applications.
In April 2012, Google's Urs Hölzle described how the company's internal network had been completely re-designed over the previous two years to run under OpenFlow with substantial efficiency improvement.
In January 2013, NEC unveiled a virtual switch for Microsoft's Windows Server 2012 Hyper-V hypervisor, which is designed to bring OpenFlow-based software-defined networking and network virtualisation to those Microsoft environments.
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