PCNSE Secure Access and VPN Practice Question
After upgrading a firewall pair from PAN-OS 9.1 to 10.0, a route-based IPsec VPN to a partner is no longer establishing. The tunnel is configured with a tunnel interface (tunnel.1) with IP 10.0.0.1/30 and the remote tunnel interface is 10.0.0.2/30. IKE phase 1 completes successfully, but phase 2 fails with 'no proposal chosen' on both sides. Both firewalls have identical IPsec crypto profiles (ESP-AES-256, SHA-256, DH-5, 1-hour lifetime). What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often assume identical crypto profiles guarantee Phase 2 success, overlooking that proxy IDs (traffic selectors) must also match between peers, especially after an upgrade that may reset these settings.
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 proxy ID configuration was removed during the upgrade
During a PAN-OS upgrade, proxy ID configurations for route-based IPsec VPNs can be lost or reset to default values. Since the tunnel uses a numbered tunnel interface (10.0.0.1/30), the firewall automatically generates proxy IDs based on the tunnel interface IP and remote tunnel interface IP. If the proxy IDs are missing or mismatched after the upgrade, Phase 2 fails with 'no proposal chosen' even though the crypto profiles match. The fix is to verify and reconfigure the proxy IDs under the IPsec tunnel configuration.
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 tunnel interface IP address conflicts with another interface
Why it's wrong here
Phase 1 would fail if there were an interface issue.
- ✗
The new PAN-OS version requires a stronger DH group for IPsec
Why it's wrong here
The IPsec profile is unchanged and matches; DH group for IPsec is usually not required.
- ✓
The proxy ID configuration was removed during the upgrade
Why this is correct
Proxy IDs are required for route-based VPNs to map traffic; if missing, phase 2 fails.
- ✗
A security policy block IKE is blocking the tunnel
Why it's wrong here
Phase 1 succeeded, so security policy for IKE is fine.
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.
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNSE practice question is part of Courseiva's free Palo Alto Networks 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 PCNSE exam.