A network engineer is documenting how a traditional distributed network differs from an SDN architecture that separates the control plane from the data plane. In the SDN model, which function does the centralised controller take over from the individual forwarding devices?
- APhysically rewriting frames and pushing packets out of egress interfaces at line rate
- BStoring the MAC address table and performing per-frame hardware lookups inside the ASIC
- CGenerating link-state hello packets on every interface to keep neighbour adjacencies alive
- DBuilding the forwarding logic and reachability decisions, then programming the resulting state down to the switches Correct
Why A is wrong: Tempting because the controller manages forwarding, but actually moving frames out of interfaces at line rate is the data plane function that stays on each switch, not the controller.
Why B is wrong: Per-frame ASIC lookups against the MAC table are data plane operations performed locally on the switch hardware, so this is not what the controller centralises.
Why C is wrong: This describes a traditional distributed control protocol running independently on each device, which is exactly the per-device behaviour an SDN controller replaces rather than performs on their behalf.
Why D is correct: Separating the control plane means the controller computes routing and forwarding intelligence centrally and pushes the resulting forwarding state to the devices, which keep only the data plane.