Which plane is centralized in software-defined networking?

The application plane in SDN interacts with the controller to define network policies and services but is not the plane that is inherently centralized.

The services plane is a conceptual layer often associated with SDN for delivering network services, but it is not the primary plane that is centralized by the SDN architecture itself.

The data plane (or forwarding plane) remains distributed across individual network devices, executing the forwarding instructions provided by the centralized control plane.

Software-Defined Networking (SDN) is characterized by the centralization of the control plane, which is responsible for network intelligence and determining how traffic paths are established and managed, separate from the data plane.