Cisco CCNA (200-301)Automation and ProgrammabilityEasy
A network architect is explaining SDN architecture to a junior engineer. She states that the controller communicates directly with switches and routers to push configuration and collect telemetry, effectively separating this function from application logic. Which plane does this controller-to-device communication represent?
- AData plane
- BControl plane
- CApplication plane
- DManagement plane
Show answer & explanationAnswer & explanation
Correct answer: B. Control plane
In SDN, the controller centralizes the control plane, making forwarding decisions and pushing them to devices via southbound protocols (e.g., OpenFlow, NETCONF). The data plane remains on the devices, simply forwarding traffic based on instructions received.
Why the other options are wrong
- A. The data plane only forwards packets; it does not make the decisions the controller pushes.
- C. The application plane sits above the controller, consuming northbound APIs, not communicating directly with devices.
- D. Management plane refers to device administration, not forwarding-decision logic sent by the controller.
SDN Control Plane Centralization
In SDN, the control plane logic is removed from individual devices and centralized in a controller, which then pushes forwarding instructions to devices' data planes.
- Controller = brain, devices = muscle
- Southbound APIs connect controller to devices (OpenFlow, NETCONF, RESTCONF)
- Separates decision-making from packet forwarding
Memory trick: Control plane thinks, Data plane forwards, Management plane configures.