Question 286 of 504
PCNSE Secure Access and VPN Practice Question
A company configures site-to-site VPN between two Palo Alto Networks firewalls using IKEv2. The tunnel does not come up. The administrator checks the IKE gateway configuration on both sides and sees matching pre-shared keys, IKE version, and encryption algorithms. What is the most likely remaining issue?
⚠ Common exam trap
It's easy for candidates to assume matching pre-shared keys and encryption algorithms guarantee tunnel establishment, overlooking the fundamental requirement that the IKE gateway's local and peer IP addresses must be correctly mirrored on both sides.
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 local and peer IP addresses are swapped on one side.
If the local and peer IP addresses are swapped on one side, the IKE gateway configuration will not match the expected endpoints. IKEv2 requires that each side's local address corresponds to the other side's peer address; a mismatch prevents the initial IKE_SA_INIT exchange from completing, as the firewalls will not recognize each other as valid peers despite matching pre-shared keys and algorithms.
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 is not assigned to a security zone.
Why it's wrong here
The tunnel interface can be assigned after the tunnel is up; it does not prevent IKE negotiation.
- ✗
Dead peer detection (DPD) is not configured.
Why it's wrong here
DPD is not required for tunnel establishment.
- ✓
The local and peer IP addresses are swapped on one side.
Why this is correct
If the local and peer IPs are reversed, the IKE negotiation will fail because the peer expects the opposite.
- ✗
The MTU on the WAN interface is set too low.
Why it's wrong here
MTU issues can cause fragmentation but not failure to establish the tunnel.
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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Last reviewed: Jun 11, 2026
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.
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