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Interview question · Network Security & Protocols

How does NAT actually work, how do peers get through it, and why is 'we are behind NAT' not a security control?

NAT drops unsolicited inbound packets as a side effect of bookkeeping, not policy. Port forwards, UPnP, outbound connections and IPv6 all walk around it.

mediumEssentialNewPreparation tags: Google, Microsoft, CiscoUpdated Nov 2026

NAT drops unsolicited inbound packets as a side effect of bookkeeping, not policy. Port forwards, UPnP, outbound connections and IPv6 all walk around it.

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What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

A colleague says the office is safe because every machine sits behind NAT and has a private address.

  1. How does source NAT work?
  2. Why do unsolicited inbound packets get dropped?
  3. What does NAT not stop?
  4. What changes with IPv6?
  5. What actually protects the office?
  6. How would you answer the colleague?

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UP NEXT ON YOUR JOURNEY
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