Which API enables an SDN controller to communicate with applications in the application plane?

Which API enables an SDN controller to communicate with applications in the application plane?

• A. Eastbound API
• B. Northbound API
• C. Westbound API
• D. Southbound API

Answer: (B)

The key idea is how the SDN controller talks to applications outside the control plane. The Northbound API is the interface the controller provides to the application plane. It abstracts away the specifics of the underlying network devices and offers a stable, programmatic way for apps to request network behavior, query topology, set policies, and receive events or status information. This enables developers to build network applications that can steer how the network should operate without needing to manage individual switches directly. In contrast, the API that talks to the actual network devices (the southbound interface) is what the controller uses to push configurations to switches and routers. Interfaces described as eastbound or westbound typically refer to inter-controller or cross-domain orchestration communications, not direct app-to-controller interactions. So for communication between the SDN controller and applications in the application plane, the Northbound API is the appropriate choice.

The key idea is how the SDN controller talks to applications outside the control plane. The Northbound API is the interface the controller provides to the application plane. It abstracts away the specifics of the underlying network devices and offers a stable, programmatic way for apps to request network behavior, query topology, set policies, and receive events or status information. This enables developers to build network applications that can steer how the network should operate without needing to manage individual switches directly.

In contrast, the API that talks to the actual network devices (the southbound interface) is what the controller uses to push configurations to switches and routers. Interfaces described as eastbound or westbound typically refer to inter-controller or cross-domain orchestration communications, not direct app-to-controller interactions. So for communication between the SDN controller and applications in the application plane, the Northbound API is the appropriate choice.