NSE7 Advanced VPN and Zero Trust Practice Question
A FortiGate administrator receives an error during IPsec VPN configuration: 'Certificate validation failed: certificate uses weak key.' The admin is using a PKI certificate with RSA 2048-bit key. The FortiGate firmware is up-to-date. What is the MOST likely reason for this error?
Answer choices
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Correct answer & explanation
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The FortiGate has a security policy that rejects certificates with keys less than 3072 bits.
In recent FortiOS versions, a security hardening setting may require minimum RSA key size of 3072 bits. RSA 2048 is considered weak by some compliance standards and may be blocked by the 'weak key' validation check. The admin can adjust the setting or use a stronger key.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE7 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE7 exam.