PCNSE Secure Access and VPN Practice Question
Exhibit
Refer to the exhibit. CLI output: admin@PA> show vpn ipsec tunnel name Corp-VPN tunnel Corp-VPN: id 123, establishment status: initiator Phase1: state UP, IKEv2 Phase2: state DOWN, reason: no matching proposal
What is the most likely cause of Phase2 being down?
⚠ Common exam trap
Many candidates confuse Phase 1 and Phase 2 failures, incorrectly assuming that any mismatch in authentication or encryption settings (including pre-shared keys or IKE version) will cause Phase 2 to fail, when in fact those affect Phase 1, and only IPsec-specific transform set mismatches cause Phase 2 to be down while Phase 1 remains up.
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 IPSec encryption or authentication settings
Phase 2 of an IPsec VPN tunnel establishes the IPsec security associations (SAs) for encrypting and authenticating data traffic. If the Phase 2 parameters, such as encryption algorithm (e.g., AES-256 vs. AES-128), authentication algorithm (e.g., SHA-256 vs. SHA-1), or DH group (e.g., group 14 vs. group 2), do not match between peers, the IKEv2 or IKEv1 Quick Mode negotiation will fail, leaving Phase 2 down. This is the most common cause of a successful Phase 1 (IKE SA) but a failed Phase 2.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Mismatched IKE version
Why it's wrong here
IKE version mismatch causes Phase1 failure, not Phase2.
- ✓
Mismatched IPSec encryption or authentication settings
Why this is correct
'no matching proposal' indicates the IPsec proposal parameters do not match between peers.
- ✗
Wrong tunnel interface IP address
Why it's wrong here
Interface IP affects routing but not Phase2 negotiation.
- ✗
Incorrect pre-shared key
Why it's wrong here
Incorrect PSK causes Phase1 failure.
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.
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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.