156-315.81.20 Advanced VPN Design Practice Question
A remote access VPN client is failing to connect to the Security Gateway. The logs show 'IKE Phase 1 Main Mode failed to match proposal'. Which configuration component is the most likely culprit?
⚠ Common exam trap
Examinees often confuse Phase 1 proposal errors with Phase 2 encryption mismatches, leading them to troubleshoot the wrong transform sets.
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
✓
Mismatched encryption or hashing algorithms in the IKE proposal.
Phase 1 failures typically indicate a mismatch in IKE parameters, specifically encryption, integrity, or Diffie-Hellman groups between the gateway and the client. In Check Point VPNs, the gateway must strictly match the IKE proposal defined in the remote access community. Verifying these settings ensures that the security association negotiation completes successfully before Phase 2 starts, preventing connection drops during the initial handshake.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Incorrect user authentication method defined in the Access Role.
Why it's wrong here
User authentication occurs after the initial IKE negotiation succeeds. An authentication failure would trigger a Phase 2 or XAUTH error rather than a Phase 1 IKE proposal mismatch, which relates specifically to the security parameters defined in the VPN community properties for key exchange.
- ✓
Mismatched encryption or hashing algorithms in the IKE proposal.
Why this is correct
The IKE Phase 1 Main Mode requires an exact match for encryption, hash, and Diffie-Hellman group settings. If the client proposes a method not supported or configured on the gateway policy, the negotiation fails immediately, as the gateway cannot verify the security parameters of the incoming request.
- ✗
Expired certificate on the Security Gateway.
Why it's wrong here
An expired certificate usually leads to an 'IKE ID' or 'Certificate validation' error during the handshake. While this stops the connection, it is distinct from an IKE proposal mismatch, which refers to the cryptographic suite selection process occurring during the very first packets of the negotiation.
- ✗
Incorrect Office Mode IP pool allocation.
Why it's wrong here
Office Mode configuration is handled after the VPN tunnel is established and the Phase 2 Quick Mode is complete. This process assigns an internal IP to the client, which is unrelated to the cryptographic parameters negotiated during the IKE Phase 1 tunnel setup process.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
About these practice questions
This 156-315.81.20 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 156-315.81.20 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 156-315.81.20 exam.