PCNSE Troubleshoot Practice Question
An administrator is troubleshooting VPN tunnel flapping. The logs show multiple Phase 2 rekeys. The tunnel uses IKEv2 with pre-shared key. What is the most likely cause?
⚠ Common exam trap
Candidates often confuse rekey flapping with DPD or misconfiguration issues, but the specific log entry of 'multiple Phase 2 rekeys' directly points to the SA lifetime being too short, not to peer reachability or identity problems.
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 rekey time settings are too short.
Frequent Phase 2 rekeys indicate that the IPsec security associations (SAs) are being renegotiated too often. With IKEv2, the rekey time settings (e.g., lifetime seconds or kilobytes) control how long a Phase 2 SA remains active before it must be refreshed. If these values are set too short, the tunnel will flap as SAs are constantly re-established, causing intermittent connectivity.
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
A mismatched IKE version would prevent the tunnel from establishing entirely.
- ✗
Dead Peer Detection (DPD) interval too long.
Why it's wrong here
Long DPD interval would delay detection but not cause frequent rekeys.
- ✓
The rekey time settings are too short.
Why this is correct
Short rekey intervals cause the tunnel to renegotiate frequently, leading to flapping.
- ✗
Incorrect local or peer ID.
Why it's wrong here
Incorrect IDs cause authentication failure, not flapping.
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
Related to this question
About these practice questions
Courseiva writes every PCNSE question from scratch — 504 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
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.