A software-defined network exposes an API to the RIB and forwarding engine, allowing off-box control...

Comprehensive and Detailed Explanation:

B: Augmented SDN allows external applications or controllers to interact with the traditional control plane (e.g., RIB or FIB) via APIs, without fully replacing it.

A (replace) removes traditional control protocols entirely.

C (hybrid) uses both SDN and legacy control planes, but without deep integration.

D (distributed) refers to traditional decentralized control planes.

Augmented SDN enhances traditional routing with programmable control, offering near real-time visibility and dynamic response without disrupting the existing control architecture.