200-901 Network Fundamentals Practice Question
In the context of SDN, which API allows a network controller to communicate with the forwarding plane of network devices?
⚠ Common exam trap
200-901 often tests SDN API directions, and candidates may confuse northbound and southbound. The trap is remembering that southbound goes down to the devices, while northbound goes up to applications.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Southbound API
The Southbound API is used by an SDN controller to communicate with the forwarding plane (data plane) of network devices, such as switches and routers. It allows the controller to program the forwarding behavior of these devices. Northbound APIs are used for communication with applications, and eastbound/westbound APIs are used for controller-to-controller communication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Eastbound API
Why it's wrong here
Eastbound APIs expose controller capabilities to external consumers or peer controllers, not to switches. The southbound interface carries instructions to the forwarding plane via OpenFlow, NETCONF or OVSDB. Eastbound is correct when integrating orchestration systems or federating multiple controllers.
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Northbound API
Why it's wrong here
Northbound APIs let applications and orchestration tools request services from the controller; they do not reach device forwarding tables. Southbound interfaces such as OpenFlow, NETCONF and OVSDB program the data plane. Northbound is correct when an automation script needs to provision policy through the controller.
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REST API
Why it's wrong here
REST is a transport style, not the SDN interface itself; the controller reaches the forwarding plane through southbound protocols such as OpenFlow, NETCONF or OVSDB. REST is correct for northbound consumption, where applications call the controller's HTTP-based API to program policy.
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Southbound API
Why this is correct
Southbound APIs sit between the controller and the forwarding plane, carrying instructions such as OpenFlow flow-mod messages that program device forwarding tables. Northbound APIs instead expose controller capabilities upward to applications, so only the southbound interface satisfies the stem's requirement to reach network devices directly.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 200-901 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-901 exam.