The answer is that the local and peer IP addresses are swapped on one side. This is the most likely remaining issue because IKEv2 requires a strict endpoint correspondence: each firewall’s local address must match the other’s peer address for the IKE_SA_INIT exchange to succeed. Even with matching pre-shared keys, IKE version, and encryption algorithms, a swapped pair prevents the firewalls from recognizing each other as valid peers, so the site-to-site VPN IKEv2 not coming up on Palo Alto firewalls is a classic symptom of this misconfiguration. On the PCNSE exam, this scenario tests your understanding of IKE gateway fundamentals—specifically that the local and peer fields define the tunnel endpoints, not just the security policies. A common trap is to assume that identical crypto profiles guarantee connectivity, but the IP address mapping is the first thing the firewalls check. Memory tip: think of it like a phone call—if both sides dial the wrong numbers, the conversation never starts.
PCNSE Secure Access and VPN Practice Question
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.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.
Option C is correct because 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.
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.
✗
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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates 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.
Detailed technical explanation
How to think about this question
IKEv2 uses a four-message exchange (IKE_SA_INIT and IKE_AUTH) to establish the security association. The IKE gateway configuration must have the correct local and peer IP addresses because the firewall uses these to construct the IKE header's source and destination IP addresses; if swapped, the responder will see an unexpected source IP and may drop the packet or fail to match a gateway configuration. In real-world scenarios, this often occurs when copying configurations between sites without adjusting the IP addresses, leading to a silent failure that is hard to diagnose without packet captures.
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.
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.
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: The local and peer IP addresses are swapped on one side. — Option C is correct because 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.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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