Preparing for a network engineer interview: what they ask and how to answer

Interviews for junior network, NOC and support roles follow a fairly predictable pattern. Interviewers want to know three things: do you understand the fundamentals, can you troubleshoot logically, and will you be a sensible, honest colleague? Prepare for each of those and you will walk in far calmer.

Part 1: the fundamentals

Expect direct questions on the basics. You don't need textbook definitions; you need clear explanations in your own words, ideally with an example. Make sure you can explain:

• The OSI model, and which layer a switch, a router and a firewall mainly work at.
• The difference between TCP and UDP, with an application that uses each.
• What happens when you type a web address into a browser, from DNS to the page loading.
• How DHCP gives a device an address (the four DORA messages).
• What a VLAN and a trunk are, and why we use them.
• The difference between static and dynamic routing, and what OSPF does.
• What NAT is and why home routers use it.

Part 2: subnetting on the spot

Many interviewers ask a quick subnetting question with no calculator: "How many usable hosts in a /27?" or "Which network does 192.168.10.77/26 belong to?" Practise until these take you under a minute. The subnetting in your head method and the subnetting practice will get you there. Say your working out loud; interviewers value a clear method more than speed.

Part 3: the troubleshooting scenario

This is often the most important part. You will hear something like: "A user says they can't reach the internet. What do you do?" There is no single right answer. They want to hear a logical, layered approach:

1. Ask questions first: one user or many? Wired or wireless? Did anything change?
2. Check the physical layer: cable, link lights, Wi-Fi connection.
3. Check the IP settings: does the device have a valid address, mask, gateway and DNS server? An address starting 169.254 means DHCP failed.
4. Ping the gateway, then an external IP address, then a name. Each result narrows down the layer at fault.
5. If the name fails but the IP works, it is DNS.
6. Document what you found and escalate with evidence if needed.

Our "no internet" playbook and the troubleshooting methodology note follow exactly this pattern. Practise saying it out loud.

Part 4: the behaviour questions

"Tell me about a time when you..." questions check how you work with people. Prepare four or five short stories using the STAR structure: Situation, Task, Action, Result. Good topics:

• A difficult problem you solved, even in a home lab or a college project.
• A time you made a mistake and how you put it right.
• Helping a frustrated user or customer.
• Learning something new quickly.

The "mistake" question is a test of honesty. Pick a real but manageable example, explain what you learnt and what you now do differently. Never claim you have never made one.

Part 5: your own projects

If you have lab projects or a portfolio, expect questions about them. Choose one you know well and be ready to draw it on a whiteboard or explain it in two minutes: what you built, a problem you hit and how you fixed it. Interviewers can tell quickly whether you really did the work.

When you don't know the answer

You will get a question you can't answer. That's normal. Don't guess wildly. Say what you do know, then how you would find out: "I haven't configured BGP myself, but I know it's the routing protocol between organisations on the internet. I'd start with the vendor documentation and test it in a lab." That answer shows honesty and a method, which matter more than one fact.

Questions to ask them

Always have two or three ready. For example: what does a typical week look like for this role? What equipment and tools does the team use? How do new starters learn, and is there support for certifications? These show genuine interest and help you decide if the job suits you.

The day before

• Re-read the job advert and match each requirement to an example from your experience.
• Look up the company: what it does, its size, and any recent news.
• Prepare your setup if the interview is online: tested camera, quiet room, charged laptop.
• Sleep. A rested brain subnets faster than a tired one.

Tip: after each interview, write down every question you were asked. Whether you get the job or not, the list makes the next interview much easier.