200-901 Network Fundamentals Practice Question
A DevOps engineer is automating network configuration using REST APIs. The engineer needs to choose between NETCONF and OpenFlow as southbound protocols. Which TWO statements are correct?
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
✓
OpenFlow allows the controller to install flow entries in switches
Option A is correct because OpenFlow is a southbound protocol in SDN in which the controller pushes flow entries (match/action rules) into the flow tables of OpenFlow-enabled switches to dictate forwarding behavior. Option E is correct because NETCONF is a configuration protocol that models device data with YANG and encodes messages in XML over SSH (port 830), making it well suited for automated configuration management. Option B is wrong because NETCONF handles configuration and state retrieval, not real-time per-packet forwarding control, which is OpenFlow's role. Option C is wrong because both NETCONF and OpenFlow are southbound protocols, not northbound APIs. Option D is wrong because OpenFlow is primarily a forwarding-plane control protocol, whereas configuration management is NETCONF's domain.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
OpenFlow allows the controller to install flow entries in switches
Why this is correct
OpenFlow is a southbound protocol where the controller pushes match-action flow entries directly into switch flow tables, governing forwarding behaviour. This programmatic control of forwarding matches the automation scenario, distinguishing it from NETCONF's configuration-focused role.
- ✗
NETCONF provides real-time packet forwarding control
Why it's wrong here
NETCONF edits and retrieves device configuration through YANG data models; it does not control real-time packet forwarding, which is OpenFlow's function via flow tables. It is tempting because NETCONF is a southbound protocol, but its scope is configuration, not per-packet forwarding decisions.
- ✗
Both protocols are used exclusively for northbound APIs
Why it's wrong here
NETCONF and OpenFlow are southbound protocols, sitting between a controller and network devices; northbound APIs face the controller and expose abstractions to applications. It is tempting because both protocols are used in SDN architectures, but their position is below the controller, not above it.
- ✗
OpenFlow is primarily used for configuration management
Why it's wrong here
OpenFlow manipulates flow tables to control packet forwarding on switches; it does not perform device configuration management, which is NETCONF's role via YANG-modelled operations. It is tempting because OpenFlow is a southbound protocol used in SDN, but its purpose is forwarding-plane programmability, not configuration.
- ✓
NETCONF uses YANG data models and XML encoding
Why this is correct
NETCONF carries configuration and state data encoded in XML and modelled by YANG, giving structured, vendor-neutral schemas. This satisfies the automation requirement for standardised device configuration, unlike OpenFlow, which manipulates forwarding tables rather than modelled configuration.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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