156-215.81.20 VPN Basics Practice Question
Exhibit
vpn debug mon [IKE] Peer 10.0.0.1: Phase 1 failure [IKE] Error: Authentication failed (Pre-shared key mismatch)
Refer to the exhibit. An administrator is troubleshooting a site-to-site VPN connection. Based on the debug log provided, what is the most likely cause of the issue?
⚠ Common exam trap
Candidates frequently jump to conclusions about phase 2 encryption settings or routing issues, ignoring the explicit error message regarding a pre-shared key mismatch in the phase 1 logs.
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
✓
Pre-shared key mismatch
The log explicitly points to a 'Pre-shared key mismatch'. This error occurs when the PSK configured on the local gateway does not match the PSK configured on the remote peer. Because the authentication phase (Phase 1) fails immediately, no tunnel is established. The administrator must verify the character-by-character accuracy of the secret on both peer devices to resolve this authentication failure and allow the tunnel to initialize properly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Encryption domain mismatch
Why it's wrong here
Encryption domain issues usually manifest during Phase 2 or when trying to route traffic through the tunnel. A PSK mismatch is specific to Phase 1 authentication and occurs before the gateways even attempt to discuss their respective encryption domains or traffic selectors.
- ✓
Pre-shared key mismatch
Why this is correct
The debug log explicitly identifies an authentication failure due to a pre-shared key mismatch. This confirms that the peer gateways failed the initial handshake because the shared secret used to verify the identity of the remote peer is not identical on both sides.
- ✗
Expired certificate
Why it's wrong here
If a certificate had expired, the error message would specifically indicate a certificate validation error or an invalid signature. Since the log identifies a PSK issue, the authentication mechanism being used is clearly PSK, not certificate-based authentication, making this option technically incorrect.
- ✗
IKE version mismatch
Why it's wrong here
An IKE version mismatch typically results in a 'No proposal chosen' or a negotiation timeout error rather than an explicit authentication failure. While version differences cause handshake issues, they do not trigger the specific error message provided in the debug output.
Visual reference
About these practice questions
This 156-215.81.20 question is part of Courseiva's 210-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 156-215.81.20 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 156-215.81.20 exam.