SDN & Virtualization Interview Questions – Expert Scenario Based (20 Q&A)
This page provides expert-level SDN & Virtualization interview questions covering architecture, control & data plane separation, NFV, VMs, containers, real-field failures and lab troubleshooting. These questions are designed for Network Architects, Cloud Engineers, Telecom Professionals and DevOps roles.
Conceptual & Architecture Questions
Q1. What problem does SDN solve in traditional networks?
SDN decouples control plane from data plane, enabling centralized control, programmability and faster network innovation.
Q2. Difference between SDN and traditional networking?
Traditional networks use distributed control logic in devices, whereas SDN centralizes control via a controller.
Q3. What is the role of an SDN controller?
The controller manages flow rules, network policies and provides a global view of the network.
Q4. How does virtualization complement SDN?
Virtualization abstracts compute, storage and network resources, while SDN provides programmable connectivity between them.
SDN Control & Data Plane Scenarios
Q5. What happens when a packet does not match any flow rule?
The switch forwards the packet to the SDN controller, which decides the appropriate forwarding action.
Q6. How does OpenFlow enable SDN?
OpenFlow allows controllers to program flow tables in switches using match–action rules.
Q7. How do you ensure scalability in SDN?
Using distributed controllers, hierarchical control and proactive flow installation.
Q8. What happens if SDN controller fails?
Redundant controllers and failover mechanisms ensure network continuity.
NFV & Virtualization Scenarios
Q9. What is NFV and how is it different from SDN?
NFV virtualizes network functions like firewall and load balancer, while SDN controls traffic forwarding.
Q10. VM vs Container – which is better for NFV?
Containers are lightweight and faster, while VMs provide stronger isolation. Choice depends on use case.
Q11. What is a VNF lifecycle?
Instantiation, scaling, healing, updating and termination of virtual network functions.
Q12. How does orchestration work in NFV?
Orchestrators manage resources, VNF placement and service chaining automatically.
Real Field & Log Analysis Scenarios
Q13. Traffic drops after VNF scaling – why?
Incorrect service chaining, delayed routing updates or resource exhaustion can cause traffic drops.
Q14. How do you troubleshoot SDN flow issues?
Inspect flow tables, controller logs and packet counters on switches.
Q15. Why does latency increase in virtualized networks?
Overlay encapsulation, CPU contention and virtual switching overhead can increase latency.
Q16. How do you monitor SDN & NFV systems?
Using telemetry, controller metrics, VNF KPIs and infrastructure monitoring tools.
LAB & Hands-On Scenarios
Q17. In lab, OpenFlow rules not applied – debugging?
Verify controller connectivity, switch registration and flow rule syntax.
Q18. How do you test VNF scaling in lab?
Generate traffic load, observe auto-scaling behavior and verify service continuity.
Q19. Lab shows packet loss in overlay network – why?
MTU mismatch, encapsulation overhead or tunnel misconfiguration.
Q20. How do you design an SDN & NFV stress test?
Simulate high traffic, controller load, VNF scaling events and observe performance KPIs.
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