What Does Hybrid Software-Defined-Network (Hybrid SDN) Mean?
A hybrid software-defined network (hybrid SDN) is a networking approach in which traditional networking and software-defined network (SDN) protocols are used and operate in the same environment. In SDN, the control is passed to a controller software application instead of the hardware. With a hybrid SDN, network engineers were able to develop new SDN technologies and support switched fabrics throughout multi-vendor hardware and application-specific integrated circuits. This essentially allowed traditional networking hardware or legacy environments to run SDN technology, like OpenFlow, without the need for a complete infrastructure overhaul.
Techopedia Explains Hybrid Software-Defined-Network (Hybrid SDN)
Two major approaches have gained popularity. Their differences in pedigree and implementation make each one useful to different markets, but not so much that it causes fragmentation.