The value of the SDN architectural approach (Which is what SDN is, it isn’t a network solution and doesn’t do anything in and of itself, but rather lends itself to building solutions with global network view and more abstracted APIs than the device or flow table model) and controllers with their associated NBI, is that it completely abstracts the details of what southbound API is used to talk to the network devices. A controller based on the SDN architectural approach may or may not speak OpenFlow and the answer to that question is a solid “don’t care” from the Orchestration and Cloud OS layer talking to the NBI in the cloud stack. The power of SDN is that a controller can expose a network abstraction and the details of the device level implementation are completely hidden. I completely agree that developing, sharing, and eventually standardizing NBI is important and has the ability to be a game changer, but this is completely orthogonal to whether OpenFlow is the only, or even a good, south bound protocol to control some or all of the forwarding behaviors in a network. The ONF initially made the horrible mistake of positioning SDN as the tail and OpenFlow as the dog when they launched. Now that the interesting conversation in the industry is about the NBI, the ONF is at risk of becoming even more irrelevant in future because they don’t appear to understand that the NBI is the key to integrating virtual networking with the on-its-way-to-ubiquity cloud movement. The most innovative and important data center SDN solutions are being build without the not-yet-ready-to-control-anything-but-the-forwarding table OpenFlow protocol and the ONF needs to have jurisdiction over the interesting decisions for the industry or become super-irrelevant as the flow-table-wire-protocol foundation. NBI is really important, but that has almost nothing to do with OpenFlow and whether it will ever be a comprehensive protocol for controlling network devices.
I have always believe this to be the only value of sdn as a whole. Meaning the ability to configure complex protocols on multiple devices. Openflow as it is today provides the transport but you will need a lot more implementation at the controller level to make this attractive long term
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