PCNSE Secure Access and VPN Practice Question
An IPSec tunnel between two PA firewalls fails to establish. On the initiator, 'show vpn ipsec-sa' shows no SAs. Which debug command would provide the most detailed information about IKE negotiation?
⚠ Common exam trap
Many candidates confuse 'debug flow basic' (data-plane) with IKE debugging (control-plane), or assume 'show counter global' will reveal negotiation failures, when in fact counters only track post-establishment statistics and not the IKE handshake itself.
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
✓
debug ike global on
'debug ike global on' enables detailed IKE (Internet Key Exchange) debugging on Palo Alto firewalls, capturing Phase 1 and Phase 2 negotiation messages, including proposal mismatches, authentication failures, and timeout errors. Since no IPsec SAs exist, the issue lies in IKE negotiation, and this command provides the most granular, real-time output to diagnose why the tunnel fails to establish.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
show counter global | match ipsec
Why it's wrong here
Counters show aggregate statistics, not real-time negotiation details.
- ✗
show log system
Why it's wrong here
System logs may include IKE errors but are less detailed than debug IKE.
- ✓
debug ike global on
Why this is correct
This command enables detailed IKE debug logs, showing negotiation steps.
- ✗
debug flow basic
Why it's wrong here
Debug flow basic shows flow table operations, not IKE negotiation.
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.