- A
Dead peer detection interval
Why wrong: DPD intervals can differ and do not prevent tunnel establishment.
- B
IKE encryption algorithm
The encryption algorithm must match for phase 1.
- C
IKE authentication algorithm
The authentication algorithm (hash) must match.
- D
Local certificate
Why wrong: Certificates do not need to match; they must be trusted by the other peer.
- E
IKE version (v1 or v2)
Both peers must use the same IKE version.
Question 27 of 516
IKE Parameters That Must Match for IPsec Tunnel Establishment
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.
Which THREE factors must match between two IKE peers for successful IPsec tunnel establishment? (Choose three.)
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
✓
IKE encryption algorithm
IKE peers must agree on the encryption algorithm (e.g., AES-256, 3DES) to protect the IKE phase 1 negotiation traffic. If the algorithms do not match, the peers cannot establish a secure SA, and the tunnel fails. This is a mandatory parameter in the IKE proposal.
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.
- ✗
Dead peer detection interval
Why it's wrong here
DPD intervals can differ and do not prevent tunnel establishment.
- ✓
IKE encryption algorithm
Why this is correct
The encryption algorithm must match for phase 1.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
IKE authentication algorithm
Why this is correct
The authentication algorithm (hash) must match.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Local certificate
Why it's wrong here
Certificates do not need to match; they must be trusted by the other peer.
- ✓
IKE version (v1 or v2)
Why this is correct
Both peers must use the same IKE version.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'factors that must match' with 'factors that can be different'—DPD intervals and certificate requirements are not mandatory for tunnel establishment, while IKE version, encryption, and authentication algorithms are non-negotiable.
Detailed technical explanation
How to think about this question
During IKE phase 1, peers exchange proposals containing a transform set that includes encryption, authentication, Diffie-Hellman group, and lifetime. The initiator sends all supported proposals, and the responder selects the first matching one. If no match exists, the SA negotiation fails with a 'no proposal chosen' error. In real-world scenarios, misconfigured encryption algorithms are a common cause of VPN failures, especially when migrating from legacy algorithms like 3DES to AES.
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.
- →
Secure Access and VPN — study guide chapter
Learn the concepts, then practise the questions
- →
Secure Access and VPN practice questions
Targeted practice on this topic area only
- →
All PCNSE questions
516 questions across all exam domains
- →
Palo Alto Networks Certified Network Security Engineer PCNSE study guide
Full concept coverage aligned to exam objectives
- →
PCNSE practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related PCNSE practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Manage, Monitor and Operate practice questions
Practise PCNSE questions linked to Manage, Monitor and Operate.
Securing Traffic and App-ID practice questions
Practise PCNSE questions linked to Securing Traffic and App-ID.
Securing Users and Applications with Authentication practice questions
Practise PCNSE questions linked to Securing Users and Applications with Authentication.
Decryption and SSL Inspection practice questions
Practise PCNSE questions linked to Decryption and SSL Inspection.
Managing Troubleshooting and High Availability practice questions
Practise PCNSE questions linked to Managing Troubleshooting and High Availability.
Deploy and Configure Firewalls practice questions
Practise PCNSE questions linked to Deploy and Configure Firewalls.
Core Concepts and Architecture practice questions
Practise PCNSE questions linked to Core Concepts and Architecture.
Secure Access and VPN practice questions
Practise PCNSE questions linked to Secure Access and VPN.
Troubleshoot practice questions
Practise PCNSE questions linked to Troubleshoot.
PCNSE fundamentals practice questions
Practise PCNSE questions linked to PCNSE fundamentals.
PCNSE scenario practice questions
Practise PCNSE questions linked to PCNSE scenario.
PCNSE troubleshooting practice questions
Practise PCNSE questions linked to PCNSE troubleshooting.
Practice this exam
Start a free PCNSE practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: IKE encryption algorithm — IKE peers must agree on the encryption algorithm (e.g., AES-256, 3DES) to protect the IKE phase 1 negotiation traffic. If the algorithms do not match, the peers cannot establish a secure SA, and the tunnel fails. This is a mandatory parameter in the IKE proposal.
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. What is the most likely cause of Phase2 being down?
easy- A.Mismatched IKE version
- ✓ B.Mismatched IPSec encryption or authentication settings
- C.Wrong tunnel interface IP address
- D.Incorrect pre-shared key
Why B: Phase 2 of an IPsec VPN tunnel establishes the IPsec security associations (SAs) for encrypting and authenticating data traffic. If the Phase 2 parameters, such as encryption algorithm (e.g., AES-256 vs. AES-128), authentication algorithm (e.g., SHA-256 vs. SHA-1), or DH group (e.g., group 14 vs. group 2), do not match between peers, the IKEv2 or IKEv1 Quick Mode negotiation will fail, leaving Phase 2 down. This is the most common cause of a successful Phase 1 (IKE SA) but a failed Phase 2.
Keep practising
More PCNSE practice questions
- Arrange the steps to enable and configure GlobalProtect on a Palo Alto Networks firewall.
- Order the steps to upgrade the PAN-OS software on a standalone firewall.
- An administrator notices that traffic from zone A to zone B is being dropped silently. Security rules are in place. Trou…
- Which component of the PAN-OS architecture is responsible for processing security policies and performing packet inspect…
- A company has configured a security policy that allows HTTP traffic from the internal network 10.0.0.0/8 to the internet…
- An organization wants to map user identity from Active Directory for traffic coming from internal LAN users without inst…
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.
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.