CCSM Advanced VPN Troubleshooting Practice Question
A Check Point Security Gateway is experiencing intermittent VPN tunnel failures. The logs show 'Phase 2 completion failed' with the reason 'No proposal chosen'. Which of the following is the most likely cause?
⚠ Common exam trap
A common mix-up: candidates confuse Phase 2 proposal mismatch with Phase 1 issues like shared secret or firewall blocks, even though the error clearly points to Phase 2 negotiation.
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 IPsec Phase 2 proposal (encryption and integrity algorithms) does not match between peers.
The 'No proposal chosen' error during Phase 2 completion indicates that the gateways could not agree on the IPsec parameters for the Phase 2 SA. This is most often caused by mismatched encryption or integrity algorithms in the Phase 2 proposal. Each gateway sends its list of supported proposals; if there is no common proposal, the negotiation fails. Verifying and aligning the Phase 2 proposals on both peers 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 tunnel is blocked by a firewall rule.
Why it's wrong here
A firewall rule blocking the VPN tunnel would prevent the tunnel from establishing entirely or cause traffic to be dropped, but it would not produce a 'No proposal chosen' error during Phase 2. That error is specific to the IPsec proposal negotiation, indicating a mismatch in algorithms, not a policy block. Firewall issues would typically manifest as drops or timeouts, not proposal rejection.
- ✗
The Phase 1 shared secret is incorrect.
Why it's wrong here
An incorrect Phase 1 shared secret would cause Phase 1 authentication to fail, typically with a 'Phase 1 completion failed' or 'Authentication failed' message. Since the error is specifically about Phase 2 completion, Phase 1 must have succeeded. Therefore, the shared secret is not the issue.
- ✓
The IPsec Phase 2 proposal (encryption and integrity algorithms) does not match between peers.
Why this is correct
The 'No proposal chosen' error in Phase 2 indicates that the two gateways could not agree on a set of IPsec parameters for the Phase 2 SA. This is typically due to mismatched encryption or integrity algorithms in the Phase 2 proposal. Each peer offers its configured proposals, and if there is no overlap, the negotiation fails. Checking and aligning the Phase 2 proposals on both gateways resolves this issue.
- ✗
The peer gateway is using a different Diffie-Hellman group for Phase 2.
Why it's wrong here
While a Diffie-Hellman group mismatch can cause Phase 2 failures, the error message would typically be different, such as 'Diffie-Hellman group mismatch' or 'Invalid KE payload'. 'No proposal chosen' specifically points to a mismatch in the encryption and integrity algorithms (the proposal), not the DH group. However, if PFS is enabled, the DH group is part of the proposal, so a mismatch there could also result in 'No proposal chosen'. But the most common cause is algorithm mismatch.
Visual reference
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.
About these practice questions
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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.