SDN, however, is not just a startup play. Nearly all the incumbent hardware vendors including Cisco, HP and Dell recognize that customers and developers will want to adopt technology that lets applications have better access and manage networking resources. As a result, they have pretty much adopted OpenFlow as a standard protocol to allow applications access to their networking gear features.
However, the hardware vendors insist that open-source technology cannot access or take advantage of all the services provided by their gear, and so in parallel to OpenFlow they are still developing their proprietary APIs as well.
Most of the hardware vendors also joined the Linux Foundation's OpenDaylight Project for developing a common platform for sending APIs to applications that enable those applications to work with multiple SDN protocols including OpenFlow, other standard protocols, and networking vendor-specific interfaces.