Network Administrator interview questions and answers

"A user says the internet is not working. What do you do?"

Show a method, not a list of guesses. Start with scope: is it one user, one floor or everyone? Then work upward from the physical layer. Check the cable or wireless connection, then whether the device has a valid address, then whether it can reach the default gateway, then an outside address by IP, and finally whether name resolution works.

A strong answer names the tool at each step, such as ipconfig /all, a ping to the gateway, a ping to a public IP address, and nslookup. It ends by saying you would record what you found and tell the user when it is fixed.

"How would you set up VLANs for an office with staff, guests and IP phones?"

Put each group in its own VLAN so their traffic is separated: one for staff, one for guests, one for voice. Guests should reach the internet but not internal systems, so an access control list or firewall rule should block guest traffic to internal subnets. Voice traffic benefits from quality-of-service marking so calls stay clear when the network is busy.

Mention the details that show experience. Trunks between switches should carry only the VLANs they need. The native VLAN should not be left on the default. Each VLAN needs its own DHCP scope, or a DHCP relay on the router or layer 3 switch.

"Explain what happens when a laptop joins the network and gets an address."

Describe the DHCP exchange in order: Discover, Offer, Request, Acknowledge. The laptop broadcasts a Discover, a DHCP server offers an address, the laptop requests that address, and the server acknowledges it with the lease details: address, mask, default gateway and DNS servers.

Then add what happens when it fails. With no reply, Windows gives itself a 169.254.x.x link-local address, which is why seeing that address points straight at a DHCP problem.

"A switch port keeps going down. What would you check?"

Look for evidence before replacing hardware. Check the logs and the interface counters for errors, and check whether port security shut the port down after seeing an unexpected MAC address. Look for a speed or duplex mismatch with the connected device. Then test the cable and try the device on a known-good port.

Panels like candidates who separate likely causes from expensive ones and rule out the cheap ones first.

"How do you make changes without causing outages?"

Talk about change control. Plan the change and write down how you would roll it back. Save a copy of the running configuration before touching anything. Agree a time when an interruption matters least, and warn the people who will be affected.

After the change, test that services work and update the documentation. If a change of yours has caused a problem in the past, say so and explain what you did differently afterwards. Panels trust honesty about a mistake more than a record that sounds perfect.

"How would you secure the wireless network?"

Use WPA3 where devices support it, and WPA2 with AES where they do not. For staff, 802.1X authentication against a central directory is stronger than a shared password, because each account can be disabled on its own. Keep guests on a separate network that cannot reach internal systems.

Round the answer off with the basics people forget: changing default passwords on access points, keeping their firmware current, and checking for rogue access points plugged into the network.

Questions to ask the panel

One or two thoughtful questions show that you are already thinking about the job. Ask how the network is monitored today and who responds out of hours. Ask what documentation exists and how current it is. Ask what the biggest network problem was recently, and what they would want a new administrator to fix first.