NSE7 Advanced VPN and Zero Trust Practice Question
An administrator runs the CLI command 'diagnose vpn ike gateway list' and sees that a phase1 gateway is in 'UP' state, but the 'DPD' field shows 'disabled'. The tunnel is working. What is the implication?
⚠ Common exam trap
Many exam-takers assume IKE keepalives are enabled by default or that NAT-T automatically handles peer detection, but in FortiGate, DPD is the sole mechanism for detecting peer failure, and disabling it leaves the tunnel blind to remote peer outages.
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
✓
The tunnel will never detect if the remote peer goes down.
When DPD is disabled, the FortiGate does not send DPD probes to verify the remote peer's liveliness. Without DPD or any other keepalive mechanism (such as IKE keepalives, which are not used in standard IPsec VPNs), the tunnel will remain in the 'UP' state indefinitely even if the remote peer goes down. This means the tunnel will never detect peer failure, leading to blackholed traffic until the administrator manually intervenes or the tunnel is re-established by other means.
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.
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