Cybersecurity-Apprentice Network Fundamentals Practice Question
An administrator is setting up a Site-to-Site IPsec VPN tunnel on a Palo Alto Networks firewall. The VPN tunnel comes up, but traffic from the local subnet cannot reach the remote subnet. Upon checking the IPsec SA status, the phase 2 security associations are active. What is the most likely cause of the traffic failure?
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
✓
A mismatch in Proxy IDs between the local and remote peers
IPsec Phase 2 SAs being active means the tunnel is established, but if traffic fails, proxy IDs (or IKEv2 selectors) might not match, or security rules/routing are misconfigured.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A mismatch in Proxy IDs between the local and remote peers
Why this is correct
If Proxy IDs (subnet selectors) do not match on both ends of an IKEv1 IPsec tunnel, traffic matching the local policy will be dropped by the crypto engine.
- ✗
Lifetime expiration in Phase 1 negotiation
Why it's wrong here
Phase 1 lifetime mismatches prevent initial IKE SA establishment.
- ✗
DHCP relay configuration on the tunnel interface
Why it's wrong here
Tunnel interfaces do not typically use DHCP relay for site-to-site VPN traffic forwarding.
- ✗
Phase 1 Encryption algorithm mismatch (e.g., AES-256 vs AES-128)
Why it's wrong here
If Phase 1 encryption algorithms mismatch, the tunnel will fail to come up entirely.
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
Courseiva writes every Cybersecurity-Apprentice question from scratch — 177 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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Palo Alto Networks exam blueprint
This Cybersecurity-Apprentice 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 Cybersecurity-Apprentice exam.