200-901 Network Fundamentals Practice Question
Which TWO of the following are southbound protocols in SDN?
⚠ Common exam trap
The trap is confusing northbound with southbound — REST and SNMP are commonly (mis)selected as southbound, but REST is northbound and SNMP is a management protocol, not a controller-to-data-plane SDN interface.
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
✓
NETCONF
NETCONF (B) is correct because it is a southbound protocol used between an SDN controller and managed network devices, allowing configuration data to be retrieved, edited, and committed via YANG-modeled operations over SSH. OpenFlow (D) is correct because it is the classic southbound protocol that lets an SDN controller program the forwarding tables of switches in the data plane. OSPF (A) is a routing protocol used between routers to exchange topology information, not a controller-to-device SDN southbound interface. SNMP (C) is a network management protocol for monitoring and managing devices, but it is not the standard SDN southbound control protocol. REST (E) is typically a northbound API style used by applications to communicate with the SDN controller, not a southbound protocol.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
OSPF
Why it's wrong here
OSPF is a routing protocol exchanged between network devices to build forwarding tables, not a southbound interface between an SDN controller and forwarding devices. Southbound protocols include OpenFlow and NETCONF; OSPF would be correct when describing routing within the underlay or between SDN domains.
- ✓
NETCONF
Why this is correct
NETCONF is a southbound protocol: the SDN controller uses it to configure and retrieve state from managed network devices. It runs over SSH and exchanges XML-encoded configuration data, sitting below the controller in the architecture, which satisfies the stem's southbound requirement.
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SNMP
Why it's wrong here
SNMP is used for monitoring and managing device state, not for programming forwarding behaviour from an SDN controller to data-plane devices. Southbound protocols such as OpenFlow install flow entries; SNMP would be correct for polling interface statistics or receiving device traps.
- ✓
OpenFlow
Why this is correct
OpenFlow is a southbound protocol: the SDN controller pushes flow entries to switches through the OpenFlow channel, programming their forwarding tables. It operates between controller and data-plane devices, below the controller, directly satisfying the stem's southbound requirement.
- ✗
REST
Why it's wrong here
REST is a northbound API style used by applications to program the SDN controller, not a southbound protocol carrying controller-to-switch instructions. Southbound examples are OpenFlow, NETCONF and PCEP; REST would be correct for northbound application-to-controller communication.
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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.