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Which SDN protocol should I use?

At the dawn of software-defined networking, there was one SDN protocol: OpenFlow. Today, users can select from a growing number of options.

Once upon a time, there was only one protocol for software-defined networking (SDN), and it was OpenFlow. Classic SDN depended on OpenFlow for communications between the SDN controller, the brains of the network, and the data plane devices that carried out its instructions.

SDN has come to have a broader meaning, however, with increasing emphasis on centralized network virtualization and programmability, not just control/data plane separation. As this shift has occurred, other protocols have become important in the space. Cisco introduced an SDN protocol for automating propagation of policy through a network composed of smart devices rather than "blank slate" data plane devices. The rise of VMware NSX and other solutions has brought to prominence the VXLAN protocol for overlaying logical networks across existing networks. NVGRE is a similar virtualization protocol and is gaining prominence as Microsoft and others take advantage of it in their cloud environments. Geneve is an even newer virtualization protocol aimed at unifying VXLAN and NVGRE.

Given the growing number of choices, how can you decide which SDN protocol is best for you? For most, the answer is going to boil down to this: Identify which SDN solution can do what you want and need it to do in the next few years, and then use whichever protocol it supports. Certainly, OpenFlow has the broadest ecosystem of supporting vendors and technologies, but if you can't get what you need using a software-defined network based on OpenFlow, look elsewhere. In the longer run, expect a convergence of one or two protocols and migration paths to get from any deprecated protocols you might have implemented (perhaps NVGRE) to those replacing them (e.g., Geneve).

Next Steps

OpenFlow not the only game in town

Plethora of protocols contribute to SDN uncertainty

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This was last published in September 2015

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Are you more likely to use OpenFlow or an alternative SDN protocol?
VXLAN and NVGRE are encapsulation protocols. They don't provide programmable flow instantiation, which is what OpenFlow does, and that is SDN. If we are to label VXLAN and NVGRE as SDN, then we must also accept that older encapsulation protocols are SDN, too. For example, 802.1q VLAN tagging, GRE, etc.

If we do loosen the SDN term to include non-OpenFlow programmable flow instantiation (I prefer to call this simply "Programmable Networking"), then this still doesn't include encapsulation protocols as there's no programmable element to them. May I humbly suggest that dynamic routing protocols are closer to SDN than encapsulation protocols, as they do alter flow. That said, I would have to add Advanced ADC’s to the mix as they make real-time context-based decisions using state (performance/security/app experience) that is constantly altering flow decisions.
Thanks for your comment, Nathan -- great perspective and insight.