- A
Matching IKE version and encryption algorithms
These are phase 1 parameters that must match.
- B
Same firewall model
Why wrong: Different models can form VPN tunnels.
- C
Same certificate authority
Why wrong: Certificate-based authentication may use different CAs.
- D
Matching proxy IDs (local/remote subnets)
Phase 2 selectors must match to establish IPsec SA.
- E
Matching pre-shared keys or certificates
Authentication must use the same key or trusted certificates.
Question 241 of 516
IPsec VPN Tunnel Requirements: IKE Version, Proxy IDs, Authentication
This PCNSE practice question tests your understanding of troubleshoot. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 are required for a successful firewall-to-firewall IPSec VPN tunnel? (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
✓
Matching IKE version and encryption algorithms
Option A is correct because IKE (Internet Key Exchange) is the protocol that establishes the security association (SA) for an IPsec VPN. Both firewalls must agree on the IKE version (v1 or v2) and the encryption algorithms (e.g., AES-256, 3DES) during Phase 1 negotiation; a mismatch will cause the tunnel to fail to establish.
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.
- ✓
Matching IKE version and encryption algorithms
Why this is correct
These are phase 1 parameters that must match.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Same firewall model
Why it's wrong here
Different models can form VPN tunnels.
- ✗
Same certificate authority
Why it's wrong here
Certificate-based authentication may use different CAs.
- ✓
Matching proxy IDs (local/remote subnets)
Why this is correct
Phase 2 selectors must match to establish IPsec SA.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Matching pre-shared keys or certificates
Why this is correct
Authentication must use the same key or trusted certificates.
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 assume hardware or CA compatibility is required, but the PCNSE exam tests that only IKE parameters, authentication credentials, and proxy IDs must match—not the firewall model or a shared CA.
Detailed technical explanation
How to think about this question
IPsec tunnel establishment involves two phases: IKE Phase 1 (main or aggressive mode) negotiates a secure channel using matching proposals (encryption, hash, DH group), and IKE Phase 2 negotiates the IPsec SA using matching proxy IDs (local/remote subnets, protocol, port). Mismatched proxy IDs are a common cause of Phase 2 failures, even if Phase 1 succeeds. In real-world scenarios, NAT traversal (NAT-T) and dead peer detection (DPD) settings must also align for tunnel stability.
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.
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.
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FAQ
Questions learners often ask
What does this PCNSE question test?
Troubleshoot — This question tests Troubleshoot — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Matching IKE version and encryption algorithms — Option A is correct because IKE (Internet Key Exchange) is the protocol that establishes the security association (SA) for an IPsec VPN. Both firewalls must agree on the IKE version (v1 or v2) and the encryption algorithms (e.g., AES-256, 3DES) during Phase 1 negotiation; a mismatch will cause the tunnel to fail to establish.
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.
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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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