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Interview question · Network Security & Protocols

How does IPsec work: IKEv2 negotiation, security associations, ESP versus AH, tunnel versus transport mode, and NAT traversal?

IPsec is two protocols that candidates blur together: IKE, which authenticates peers and agrees keys, and ESP, which protects every packet afterwards. Keep them apart and the rest follows.

hardEssentialNewPreparation tags: Cisco, Palo Alto Networks, Check PointUpdated Nov 2026

IPsec is two protocols that candidates blur together: IKE, which authenticates peers and agrees keys, and ESP, which protects every packet afterwards. Keep them apart and the rest follows.

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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

Two offices are connected with a site-to-site IPsec VPN between their gateways, configured years ago with a pre-shared key.

  1. How does IKEv2 set up the tunnel?
  2. What protects the traffic itself?
  3. What is the risk with the old pre-shared key?
  4. What configuration checks matter?
  5. Does the tunnel make cross-office traffic trusted?
  6. How would you modernise the VPN?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
Next in this trackHow does WireGuard work: static keys, its one-round-trip handshake, cryptokey routing, and why it deliberately has no cipher negotiation?Next in this trackDesign secure VPN remote access: authentication, split vs full tunnel, DNS leaks, access after connect, and protecting the gateway.Next in this trackWhat does message signing do in SMB, LDAP, IPsec, DNSSEC and MACsec, and when is signing the right choice instead of encryption?
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