The bigger picture
SDN makes networking more dynamic and flexible by creating logical overlay networks in software without impacting the underlying physical network. The abstraction of overlay networks from the underlying physical network provides for relatively risk-free changes. Because the network controller and network agents are software only, they support faster innovation and more frequent updates than traditional networking gear.
Furthermore, the hypervisor manager and the network controller will exchange data about the systems they administer. For the first time, network engineers will have visibility into the servers and applications on their networks, providing for better operation and troubleshooting.