NSE7 Advanced VPN and Zero Trust Practice Question
A FortiGate administrator enables Dead Peer Detection (DPD) on an IPsec VPN tunnel. What is the primary purpose of DPD?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To detect when the remote peer is no longer reachable
DPD is used to monitor the liveness of the remote peer. If the peer becomes unreachable, DPD detects it and can trigger a failover or tunnel teardown, ensuring traffic does not blackhole.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
To dynamically adjust the tunnel MTU
Why it's wrong here
MTU adjustments are done via other mechanisms like PMTUD.
- ✗
To encrypt the IKE negotiation traffic
Why it's wrong here
Encryption is inherent to IKE; DPD is for liveness detection.
- ✗
To automatically renegotiate the IKE SA before it expires
Why it's wrong here
Renegotiation is based on lifetime settings, not DPD.
- ✓
To detect when the remote peer is no longer reachable
Why this is correct
DPD sends periodic messages to verify the peer is alive.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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