- A
Incorrect pre-shared key
An incorrect PSK causes phase1 negotiation to fail, bringing the tunnel down.
- B
Proxy ID mismatch
Why wrong: Proxy ID mismatch causes phase2 failure, but the tunnel state may still show as down.
- C
Tunnel interface IP misconfiguration
Why wrong: IP misconfiguration affects routing but not tunnel state directly.
- D
IKE version mismatch
Why wrong: IKE version mismatch prevents negotiation, but PSK is more commonly misconfigured.
Question 242 of 516
IPSec Tunnel Down: Incorrect Pre-Shared Key
This PCNSE practice question tests your understanding of secure access and vpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An administrator sees the IPSec tunnel state 'down' under the tunnel monitor. What is the most common cause for this issue?
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
✓
Incorrect pre-shared key
The most common cause for an IPsec tunnel showing 'down' in the tunnel monitor is an incorrect pre-shared key. During IKE Phase 1 authentication, both peers must present matching pre-shared keys; if they differ, the IKE SA negotiation fails, preventing the tunnel from coming up. This is a frequent misconfiguration because the key is manually entered and often mistyped or mismatched between endpoints.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Incorrect pre-shared key
Why this is correct
An incorrect PSK causes phase1 negotiation to fail, bringing the tunnel down.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Proxy ID mismatch
Why it's wrong here
Proxy ID mismatch causes phase2 failure, but the tunnel state may still show as down.
- ✗
Tunnel interface IP misconfiguration
Why it's wrong here
IP misconfiguration affects routing but not tunnel state directly.
- ✗
IKE version mismatch
Why it's wrong here
IKE version mismatch prevents negotiation, but PSK is more commonly misconfigured.
Common exam traps
Common exam trap: answer the scenario, not the keyword
In the Palo Alto PCNSE exam, incorrect pre-shared key is a common cause for IPsec tunnel failure. Candidates often mistake proxy ID mismatch (Phase 2) for Phase 1 authentication failures.
Trap categories for this question
Command / output trap
Proxy ID mismatch causes phase2 failure, but the tunnel state may still show as down.
Detailed technical explanation
How to think about this question
In IKEv1, the pre-shared key is used during Main Mode or Aggressive Mode authentication; a mismatch causes the IKE SA to fail at the authentication payload exchange. In IKEv2, the shared secret is used in the AUTH exchange, and a mismatch results in an AUTH_FAILED notification. Real-world scenarios often involve copying keys from a config file where hidden characters or case sensitivity cause subtle mismatches that are hard to spot.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the PCNSE exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Secure Access and VPN — study guide chapter
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FAQ
Questions learners often ask
What does this PCNSE question test?
Secure Access and VPN — This question tests Secure Access and VPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Incorrect pre-shared key — The most common cause for an IPsec tunnel showing 'down' in the tunnel monitor is an incorrect pre-shared key. During IKE Phase 1 authentication, both peers must present matching pre-shared keys; if they differ, the IKE SA negotiation fails, preventing the tunnel from coming up. This is a frequent misconfiguration because the key is manually entered and often mistyped or mismatched between endpoints.
What should I do if I get this PCNSE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on PCNSE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A firewall administrator configures an IPSec tunnel. After committing, the tunnel never becomes active. What is the most likely reason?
medium- A.The tunnel interface is not in a zone.
- ✓ B.The IKE gateway configuration is missing.
- C.The proxy-id protocol should be set to '0' for all.
- D.The crypto profile name is invalid.
Why B: B is correct because an IPSec tunnel requires both an IKE gateway configuration and an IPSec crypto profile to establish Phase 1 and Phase 2 security associations. Without the IKE gateway, the firewall has no peer address, authentication method, or pre-shared key to initiate IKEv1/v2 exchanges, so the tunnel remains down. The exhibit likely shows a tunnel interface and crypto profile but omits the IKE gateway object, which is mandatory for tunnel activation.
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Last reviewed: Jul 4, 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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