Interview prep · 6 questions
Wireless networking interview questions
What do interviewers test with wireless questions?
They test the basics of how a client finds and joins a wireless network, how that network is secured, and how radio choices affect coverage and speed. Expect a troubleshooting scenario where a client joins the network but still cannot reach anything.
Updated
Mock interview
One question at a time. Answer it out loud as you would in the room, then reveal the model answer and rate yourself honestly. Your progress stays in this browser.
What is the difference between an SSID and a BSSID?
Entry level
The SSID is the network name clients see and join, and many access points can broadcast the same one. The BSSID is the MAC address of one access point's radio for that network, so it identifies exactly which radio a client is connected to.
When several access points share an SSID, a client can roam between them and keep its settings while its BSSID changes.
One radio can carry several SSIDs, each with its own BSSID, which is how a single access point offers a staff and a guest network.
Common weak answer: Treating the two as the same thing. The SSID is a name for people; the BSSID is an address for one radio.
Likely follow-ups
- What is an extended service set?
- How does a client decide when to roam?
- Why would you map each SSID to its own VLAN?
What is the difference between WPA2-Personal and WPA2-Enterprise?
Mid level
WPA2-Personal uses one pre-shared passphrase for everyone, which is simple but means every user holds the same secret. WPA2-Enterprise authenticates each user or device separately through 802.1X and an authentication server, so access can be revoked per person and each session gets its own keys.
When someone leaves an organisation whose network uses a pre-shared key, the only real fix is changing the key on every device.
WPA3 strengthens the personal mode against password-guessing attacks and is the better choice wherever clients support it.
Common weak answer: Saying Enterprise just means a longer password. The difference is per-user authentication against a server.
Likely follow-ups
- Why is a shared key a problem when someone leaves?
- What does the authentication server do in 802.1X?
- What does WPA3 change?
What are the trade-offs between the 2.4 GHz and 5 GHz bands?
Entry level
2.4 GHz reaches further and passes through walls better, but it has only three non-overlapping channels (1, 6 and 11) and shares the air with many other devices. 5 GHz offers many more channels and higher speeds with less interference, at the cost of shorter range.
In a dense office the extra channels of 5 GHz matter more than range, because neighbouring access points can each use a channel that does not overlap.
Planning 2.4 GHz means sticking to channels 1, 6 and 11; the channels in between overlap their neighbours and cause interference.
Common weak answer: Saying 5 GHz is always better. Range and wall penetration can make 2.4 GHz the right choice.
Likely follow-ups
- Why are 1, 6 and 11 the usual 2.4 GHz channels?
- What is co-channel interference?
- When would you turn 2.4 GHz off?
What is the difference between an autonomous access point and a controller-based one?
Mid level
An autonomous access point is configured and managed on its own, bridging its wireless clients onto the wired network. Controller-based access points are managed centrally by a controller that pushes their configuration, coordinates channels and power, and handles roaming across the whole site.
A handful of autonomous access points is fine for a small office, but configuring fifty of them one at a time invites mistakes, which is the problem controllers solve.
Cloud-managed access points move the controller into a hosted service, with the same central-management idea.
Common weak answer: Saying controller-based access points send all traffic through the controller. Depending on the design, client traffic is either tunnelled to the controller or switched locally.
Likely follow-ups
- What does a controller coordinate that a single access point can't?
- What happens to clients if the controller fails?
- When is an autonomous access point the better choice?
A laptop joins the Wi-Fi network but gets no IP address. What do you check?
Mid level
Joining proves the radio side and the passphrase are fine, so the problem is on the wired side behind the access point. Check that the SSID is bridged to the right VLAN or subnet, that a DHCP server or relay serves that subnet, and that the pool still has free addresses.
A wrong passphrase stops a client before it joins at all, so "connected, no address" points away from the wireless security settings.
If other clients on the same SSID get addresses, compare this one's settings; if none do, look at the access point's uplink and the DHCP path.
Common weak answer: Changing the wireless passphrase. A client that has joined has already proved the key.
Likely follow-ups
- How would you tell a full DHCP pool from an unreachable server?
- What address would the laptop show if DHCP never answered?
- What changes if the SSID maps to a VLAN the uplink does not carry?