How does a VPN work, and what is the difference between a full tunnel and a split tunnel?
What they are really testing: Whether you understand encapsulation/encryption and the routing decision of what actually goes through the tunnel. Split versus full tunnel is a real security-versus-performance trade-off.
A real interview question
How does a VPN work, and what is the difference between a full tunnel and a split tunnel?
What most people say
drag me
“A VPN encrypts your internet so nobody can see what you are doing.”
It reduces a VPN to "encryption" and ignores the tunnel-to-a-network model and the full-versus-split routing decision, which is the operational heart of the question.
The follow-ups they ask next
A remote employee says everything is slow after connecting to the VPN. What setting likely helps?
They are probably on a full tunnel routing all traffic (including video calls and general browsing) through the gateway. A split tunnel for just the corporate ranges removes that bottleneck, weigh it against the loss of inspection.
What is the security downside of split tunnel?
Traffic that goes direct bypasses corporate filtering, DLP, and monitoring, so a compromised endpoint has an uninspected path to the internet. Some orgs accept that for performance, others mandate full tunnel.
What the interviewer is listening for
- Explains encapsulation + encrypted tunnel to a network
- Names IPsec/WireGuard
- Articulates the split vs full trade-off
What sinks the answer
- "It just encrypts your internet"
- No notion of tunneling to a specific network
- Unaware of split vs full tunnel
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“A VPN [wraps traffic in an encrypted tunnel between endpoints so it crosses the internet privately, as if on the remote network], using [IPsec or WireGuard]. Full tunnel [sends all traffic through the VPN: full inspection but slower]; split tunnel [sends only corporate-bound traffic through it: faster but the rest skips inspection]. So it is [control vs performance].”
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