Core technical questions
"Explain the OSI model and where common protocols operate." Layer 1 (Physical): cables, signals. Layer 2 (Data Link): Ethernet, MAC addresses, VLANs, STP. Layer 3 (Network): IP, OSPF, BGP, routing. Layer 4 (Transport): TCP, UDP, ports. Layers 5-7 (Session, Presentation, Application): TLS, HTTP, DNS, SMTP. Give a real example at each layer. "What is the difference between OSPF and BGP?" OSPF is an interior gateway protocol (IGP) used within a single autonomous system. It uses link-state routing and Dijkstra's algorithm to find the shortest path. BGP is the exterior gateway protocol (EGP) used between autonomous systems. BGP makes routing decisions based on policy attributes (AS path, local preference, MED) rather than shortest path. Enterprise networks typically use OSPF internally and BGP for internet peering or MPLS VPN connectivity.
Troubleshooting questions
"A user cannot access a website. Walk me through your troubleshooting approach." Structured answer: Can they access any website or only this one? Is it DNS resolution or connection? Ping the default gateway (Layer 3 connectivity), ping 8.8.8.8 (internet connectivity), nslookup the domain (DNS), traceroute to the destination, check if the site is down externally. Show a systematic method and do not skip steps. "How would you identify and resolve a network loop?" Symptoms: broadcast storm, high switch CPU, link LEDs blinking rapidly. Check STP topology (show spanning-tree), identify whether a port that should be blocking is forwarding. Disable the offending port, allow STP to reconverge. Enable BPDU Guard on access ports to prevent recurrence.
Cloud networking questions
Cloud networking is now an expected competency. "What is a VPC and how does routing work within it?" Virtual Private Cloud: isolated network in AWS/Azure/GCP; route tables control traffic between subnets; internet gateway or NAT gateway for internet access; VPC peering or Transit Gateway for multi-VPC connectivity. "What is SDN?" Software Defined Networking separates the control plane from the data plane. A centralised controller manages routing decisions rather than distributing intelligence to individual devices, enabling programmable, policy-driven network management. Knowledge of AWS VPC, Azure Virtual Network, or GCP VPC is increasingly expected for enterprise network roles.
Behavioral questions
"Tell me about a network outage you were involved in resolving." Strong answer: specific impact (users, services, duration), your specific role, root cause identified, change made to prevent recurrence. Mention a post-incident review if you wrote one. Network engineers who document outages and share learnings stand out. "Describe a change you implemented on a live network and how you managed the risk." Show change management discipline: tested in lab, rollback procedure ready, maintenance window used, monitored traffic after the change, stakeholders informed.
Certifications and how they are evaluated
Main vendor certifications: Cisco CCNA (entry-level, expected for most junior roles), CCNP (professional level, expected for mid-level), CCIE (expert level, expected for senior roles). Vendor-neutral: CompTIA Network+ (entry-level), CWNA for wireless. Cloud networking certifications (AWS Advanced Networking, Azure Network Engineer Associate) are increasingly valued. When asked about certifications, be specific about what the certification covers and what you learned, not just the badge name.