The history of OpenFlow

Computer Weekly takes a look back at the beginnings of the software-defined networking protocol and the technology behind it

If you have been following the rise of software-defined networking (SDN) recently as it makes its way into the thinking of enterprises the world over, it is likely you will have come across OpenFlow. But what exactly is OpenFlow? And what role does it have to play in SDN?

It is important to point out that OpenFlow is not SDN, and vice versa. It is one of the building blocks of a software-defined network – and a very important one at that.

OpenFlow is a protocol that separates the control of a switch from the switch itself. The high-level control of a switch, which includes packet routing and so on, is moved to a centralised server. The OpenFlow protocol allows switches and controllers that support OpenFlow to communicate with each other.

Enabling the network to be programmed independently of its gear makes the whole system much more agile and flexible, not to mention cost-effective.  

Gartner analysts Joe Skorupa and Mark Fabbi listed OpenFlow as one of the "trigger technologies" in their Hype Cycle for Networking and Communications 2012 report.

“In an OpenFlow network, the topology is centrally managed,” their description of the protocol reads. “The data plane still resides on the switch/router, while high-level routing decisions are moved to a separate controller. OpenFlow defines a set of messages that are exchanged by the controller and switch.

“OpenFlow's distinction is in a new implementation that provides discrete software options for network definition and management. OpenFlow promises to ease provisioning of large, complex datacentre networks.”

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The origins of OpenFlow

Skorupa and Fabbi go on to say OpenFlow is such a new technology that widespread adoption is still at least two years away. However, the origins of OpenFlow can be traced back to 2006, when Martin Casado, a PhD student at Stanford University in Silicon Valley, California, developed something called Ethane.

Intended as a way of centrally managing global policy, it used a “flow-based network and controller with a focus on network security”, according to, a site dedicated to tracking the emerging technology, along with SDN.

That idea eventually led to what become known as OpenFlow, thanks to more research conducted jointly by teams at Stanford and the University of California, Berkeley.

Although still a nascent technology, it was gaining a fair amount of traction in Silicon Valley. Nicira and Big Switch Networks, early backers of OpenFlow, raised significant amounts of venture capitalist funding to help push their products.

Setting standards

In 2011, the Open Networking Foundation was established, with the aim of standardising emerging technologies propelling software to the forefront of networking and datacentre management. 

While the first version of the OpenFlow protocol (listed as version 1.1) was released in February 2011, the second (version 1.2) was overseen by the Open Networking Foundation, which retains control over the specification.

Founding members include the likes of Google, Facebook and Microsoft, while the likes of Citrix, Cisco, Dell, HP, F5 Networks, IBM, NEC, Huawei, Juniper Networks, Oracle and VMware have since joined the Foundation (a full list of members is available here).

The promotion of SDN and OpenFlow will be one of the main benefits of the Foundation, according to Stu Bailey, founder and CTO of InfoBlox.

If customers adopt OpenFlow, then lock-in to a supplier's routing protocols is eliminated and customers may force switch suppliers to increasingly compete on price

Gartner Hype Cycle for Networking and Communications 2012 report

“It is a standards body driven by consumers – not suppliers – that have proven by heavy investment over the past 10 years that SDN approaches create better economies and scales within IT,” he says. “Now they are sharing much of that knowledge with the rest of the market through backing emerging standards.”

Networking hardware and software becoming a commodity

But membership of the Open Network Foundation does not necessarily translate to full support for the OpenFlow protocol. There is one simple reason for this: commoditisation.

Currently, a lot of the control and management of switches and routers is done through proprietary software installed on each bit of network kit. Moving that management to a central server, as OpenFlow does, means those boxes will become commodities. 

That is bad news for the likes of Cisco and Juniper Networks, which have built vast businesses based on selling their proprietary hardware and software paired together.

As Gartner’s report on OpenFlow states: “If customers adopt OpenFlow, then lock-in to a supplier's routing protocols is eliminated and customers may force switch suppliers to increasingly compete on price.”

Balancing open networking with proprietary business

The report goes on to suggest those companies not fully supporting OpenFlow “may attempt to delay market acceptance by offering proprietary variants or to position OpenFlow as a set of application programming interfaces (APIs) to proprietary management systems to avoid the possibility of a loss of account control and product margin erosion”.

That is one approach Cisco is taking. As the technology giant explained to Computer Weekly for our software-defined networking buyer's guide, it is helping customers to embrace open networking through its ONE strategy. This includes a set of APIs, as well as a controller framework that supports OpenFlow.

Juniper Networks may be threatened by the emerging OpenFlow protocol, but is still aware of the importance of the general shift towards more open networking. 

Speaking to Computer Weekly, Nigel Stephenson, head of cloud services marketing at the firm, spells out his company’s position, but also the importance of open standards going forward.

“In 2012, we released the JUNOS V App Engine, an appliance that allows you to run third-party applications; the other angle is to take our services and run them on other platforms,” he says. “All of this has to be in a standards-based environment. It is possible to use proprietary protocols, but that affects costs and causes lock-in, which customers do not want.

“OpenFlow is one of those standards; it has a purpose within this architecture, but it’s not the only one, and we expect more to be developed. Where there are standard protocols, we will use them. Where there are not, we need to work as an industry to make sure we standardise whatever we go forward with.”

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Embracing OpenFlow and SDN

While the approach taken by the likes of Cisco and Juniper is partly aimed at protecting their proprietary business and partly at progressing along with the rest of the networking industry, other suppliers have embraced OpenFlow and SDN wholeheartedly.

HP, which is currently undergoing a huge shift to become an end-to-end enterprise technology provider, is one company pushing its OpenFlow credentials. 

It has been collaborating on the OpenFlow protocol for over five years now, and in February 2012 made its big play, announcing the introduction of a portfolio of OpenFlow-enabled switches, covering 16 models in total and supporting more than 10 million installed ports.

HP also plans to extend OpenFlow support to its entire range of FlexNetwork products by the end of 2012.

Transforming the future of networking

There is no doubt that software-defined networking will ultimately transform the networking industry, as the benefits it can bring are simply too huge to ignore. 

"The combination of OpenFlow and SDN has the potential to transform the networking market from a bundled hardware and software market to one of separate hardware and software components. It can dramatically simplify network operations and lower complexity and costs,” says Gartner’s Skorupa.

However, while OpenFlow will undoubtedly play an important role in software-defined networking, there is a likelihood other similar protocols will emerge to operate alongside it. For now, though, OpenFlow is the clear leader and will remain so for the next few years as this technology matures and propels the networking industry forward.

Image: Thinkstock

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