The answer is to remove the pre-shared key from the IKE gateway configuration on the branch firewalls. When a site-to-site VPN certificate authentication fails after migration on Palo Alto, the root cause is often a configuration mismatch where a pre-shared key remains as a fallback. In IKEv2, the authentication method must be consistent on both peers; if one side is set to certificate-only and the other still has a PSK configured, the firewall will propose PSK authentication, triggering the 'no proposal chosen' error because the hub expects certificate-based authentication. This scenario is a classic trap on the PCNSE exam, testing your understanding that IKE gateway authentication methods are mutually exclusive—you cannot mix PSK and certificate in the same phase 1 proposal. A simple memory tip: "One method, one match—PSK and cert never catch."
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 large enterprise uses a Palo Alto Networks firewall as the central hub for site-to-site VPN connections to 50 branch offices. Each branch office has a different subnet (e.g., 10.x.0.0/16 where x is the branch number). The VPN tunnels are configured using IKEv2 with pre-shared keys. Recently, the IT team decided to migrate to certificate-based authentication for improved security. They issued certificates from an internal CA to all branch firewalls and the hub firewall. After the migration, all tunnels failed to establish. The hub firewall logs show 'IKE negotiation failed' with error 'no proposal chosen'. The administrator checks the IKE gateway configuration on the hub: the IKE version is IKEv2, the authentication method is set to 'Certificate', and the certificate profile is configured with the root CA certificate. The administrator also verifies that the branch firewalls have the correct certificates and the hub's certificate is trusted. The branch firewalls' IKE gateways are configured with the hub's IP and pre-shared key (still configured as a fallback). What should the administrator do to resolve the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the pre-shared key from the IKE gateway configuration on the branch firewalls.
When using certificate-based authentication in IKEv2, the IKE gateway configuration must use only the certificate for authentication. If a pre-shared key is also configured, the firewall will attempt to use PSK authentication instead of the certificate, causing a mismatch with the peer expecting certificate-based authentication. This results in the 'no proposal chosen' error because the authentication method proposed (PSK) does not match the expected method (certificate). Removing the pre-shared key from the branch firewalls' IKE gateway configuration forces them to use the certificate, aligning with the hub's configuration.
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.
✓
Remove the pre-shared key from the IKE gateway configuration on the branch firewalls.
Why this is correct
When using certificate authentication, the pre-shared key should not be configured; otherwise the IKE proposal negotiation fails.
Related concept
Read the scenario before looking for a memorised answer.
✗
Change the IKE version on the hub to IKEv1.
Why it's wrong here
IKE version mismatch would cause a different error.
✗
Reissue the hub firewall's certificate with the correct subject name.
Why it's wrong here
The certificate subject name is not the cause; the negotiation fails due to proposal mismatch.
✗
Ensure the internal CA is reachable from the branch firewalls.
Why it's wrong here
Certificate revocation check is not causing the failure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a pre-shared key can remain as a fallback without affecting the authentication method negotiation, but in Palo Alto Networks IKEv2, the presence of a PSK overrides certificate authentication, causing a proposal mismatch.
Detailed technical explanation
How to think about this question
In IKEv2, the authentication method is part of the SA payload proposal. When both a pre-shared key and a certificate are configured, Palo Alto Networks firewalls prioritize PSK over certificate authentication, leading to a proposal mismatch if the peer expects certificate-based authentication. The 'no proposal chosen' error occurs at the IKE_SA_INIT phase when the initiator's proposal (including authentication method) does not match any of the responder's configured proposals. Certificate-based authentication requires that both peers have no PSK configured in the IKE gateway, and the certificate profile must include the root CA certificate for chain validation.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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: Remove the pre-shared key from the IKE gateway configuration on the branch firewalls. — When using certificate-based authentication in IKEv2, the IKE gateway configuration must use only the certificate for authentication. If a pre-shared key is also configured, the firewall will attempt to use PSK authentication instead of the certificate, causing a mismatch with the peer expecting certificate-based authentication. This results in the 'no proposal chosen' error because the authentication method proposed (PSK) does not match the expected method (certificate). Removing the pre-shared key from the branch firewalls' IKE gateway configuration forces them to use the certificate, aligning with the hub's configuration.
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 →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.