CCSM Advanced VPN Troubleshooting Practice Question
A remote access VPN user authenticates successfully with a certificate but cannot access internal resources. The Security Gateway logs show 'IKE Phase 2: No valid SA' and the user's client reports 'Failed to establish tunnel'. The gateway's VPN community uses AES-256 and SHA-256 for Phase 2. Which of the following is the most likely cause?
⚠ Common exam trap
The trap here is focusing on authentication or account issues when the failure occurs after successful Phase 1 authentication, misdirecting attention from Phase 2 parameter mismatches.
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 VPN client is configured with a different Phase 2 encryption algorithm than the gateway.
The correct answer is that the VPN client and gateway have mismatched Phase 2 encryption algorithms. Phase 2 negotiation requires both peers to agree on encryption and hash algorithms; if they do not, the gateway rejects the proposal and logs 'No valid SA'. Since Phase 1 succeeded, the problem lies in the Phase 2 settings, and aligning the client's algorithm with the gateway's AES-256 resolves the issue.
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 VPN client is configured with a different Phase 2 encryption algorithm than the gateway.
Why this is correct
This is the most likely cause because a mismatch in Phase 2 encryption or hash algorithms prevents the gateway from finding a matching SA proposal, resulting in 'No valid SA'. The client might propose AES-128 while the gateway requires AES-256, or use a different hash. This directly explains why Phase 1 succeeds but Phase 2 fails, aligning with the log messages and the gateway's configured algorithms.
- ✗
The user's certificate has expired.
Why it's wrong here
An expired certificate would typically cause Phase 1 authentication to fail, not Phase 2 SA establishment. The logs indicate that Phase 1 completed successfully (certificate authentication succeeded), and the error occurs during Phase 2. Therefore, certificate expiration is not the cause of the 'No valid SA' message, which points to a mismatch in Phase 2 proposals or a policy issue.
- ✗
The user's account is locked in the LDAP server.
Why it's wrong here
An account lock would cause authentication failure during Phase 1, not Phase 2. Since the user authenticated successfully with a certificate, the account status is not the issue. The 'No valid SA' error is specific to Phase 2 negotiation, which occurs after authentication. Thus, LDAP account status is irrelevant to this problem.
- ✗
The gateway's IPsec SA lifetime is set too low, causing immediate rekey.
Why it's wrong here
A low SA lifetime might cause frequent rekeys, but it would not prevent the initial SA from being established. The error 'No valid SA' indicates that no SA could be created at all, not that an existing SA expired quickly. If the lifetime were the issue, the user might connect briefly and then disconnect, but the logs would show SA deletion rather than negotiation failure.
Visual reference
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
About these practice questions
This CCSM question is part of Courseiva's 219-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Check Point exam blueprint
This CCSM practice question is part of Courseiva's free Check Point 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 CCSM exam.