NSE4 Authentication and VPN Practice Question
An administrator runs 'diagnose vpn ike config' and sees the output includes 'P2 proposals: aes128-sha256, aes256-sha1'. What does this indicate?
⚠ Common exam trap
Many exam-takers confuse Phase 1 and Phase 2 parameters, assuming 'P2 proposals' includes Diffie-Hellman groups or lifetimes, when in fact it only specifies the encryption and authentication algorithms for the IPsec SA.
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 Phase 2 encryption and authentication algorithms
The output 'P2 proposals: aes128-sha256, aes256-sha1' from the 'diagnose vpn ike config' command specifically lists the Phase 2 (IPsec) proposals, which define the encryption and authentication algorithms used for protecting data traffic. Option C is correct because these are the Phase 2 encryption (aes128, aes256) and authentication (sha256, sha1) algorithms, not Phase 1 settings or other parameters.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Diffie-Hellman groups for Phase 2
Why it's wrong here
The output of 'diagnose vpn ike config' shows the Phase 2 proposal, which is a list of encryption and integrity algorithms for the IPsec SA — not the Diffie-Hellman group. A Diffie-Hellman group is only relevant in Phase 2 if Perfect Forward Secrecy (PFS) is enabled, and even then FortiOS displays that setting separately or omits it from this diagnostic view. Therefore, the DH group for Phase 2 is not what this command reveals.
- ✗
The Phase 1 encryption settings
Why it's wrong here
This command displays Phase 2 (quick mode) settings, not Phase 1 (main mode) settings. Phase 1 encryption algorithms, such as AES-256 or 3DES for protecting the IKE key-exchange traffic, are shown under a different diagnostic section that is explicitly labeled as the Phase 1 proposal. Since the given output concerns the second phase of IPsec, the Phase 1 encryption settings are not visible in this particular context.
- ✓
The Phase 2 encryption and authentication algorithms
Why this is correct
The 'diagnose vpn ike config' command in FortiOS prints the Phase 2 proposal, which lists the exact ESP (Encapsulating Security Payload) transforms: the encryption algorithm (e.g., AES-GCM, AES-CBC) and the authentication/integrity algorithm (e.g., SHA-256, SHA-1). This is precisely what the administrator sees in the output, making it the correct answer. It reflects the algorithms that will be used for the actual IPsec data tunnel.
- ✗
The lifetime settings for the VPN tunnel
Why it's wrong here
Lifetime settings — such as the IKE or IPsec SA expiration time in seconds or kilobytes — are not part of the 'diagnose vpn ike config' output. They are defined in the tunnel's configuration and are shown only in configuration dumps or separate debugging tools. The diagnostic output focuses on the cryptographic proposal, not temporal or volume-based limits, so lifetime settings are not what the command displays.
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 NSE4 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 NSE4 exam.