This PCNSE practice question tests your understanding of secure access and vpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Exhibit
2019-04-10 14:23:45, ERROR: ike: IKE negotiation failed: No proposal chosen (1.2.3.4 -> 5.6.7.8)
2019-04-10 14:23:45, WARN: ike: Phase 2 negotiation failed for vpn-tunnel1: no acceptable set of proposals
2019-04-10 14:23:46, INFO: ike: IPSec SA deleted (1.2.3.4 -> 5.6.7.8 spi 0x12345678)
Refer to the exhibit. A firewall log shows these messages for an IPSec tunnel. Which configuration mismatch is the likely cause?
Exhibit
2019-04-10 14:23:45, ERROR: ike: IKE negotiation failed: No proposal chosen (1.2.3.4 -> 5.6.7.8)
2019-04-10 14:23:45, WARN: ike: Phase 2 negotiation failed for vpn-tunnel1: no acceptable set of proposals
2019-04-10 14:23:46, INFO: ike: IPSec SA deleted (1.2.3.4 -> 5.6.7.8 spi 0x12345678)
A
IKE Phase 1 proposal mismatch.
Why wrong: Incorrect. Phase 1 negotiation would show earlier errors.
B
Preshared key mismatch.
Why wrong: Incorrect. Preshared key mismatch causes authentication failure in Phase 1, not proposal error.
C
IKE Phase 2 proposal mismatch.
Correct. The warning explicitly states Phase 2 negotiation failed.
D
Invalid peer IP address.
Why wrong: Incorrect. Invalid peer IP would prevent IKE initiation.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
IKE Phase 2 proposal mismatch.
The log messages indicate that IKE Phase 1 completed successfully (as shown by the 'IKE Phase 1 established' message), but Phase 2 negotiation failed. This points directly to a mismatch in the IKE Phase 2 proposal parameters, such as the IPsec security protocol (ESP vs AH), encryption algorithm, authentication algorithm, or Diffie-Hellman group used for PFS. A Phase 2 proposal mismatch prevents the creation of the IPsec SA, even though the IKE SA is already established.
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.
✗
IKE Phase 1 proposal mismatch.
Why it's wrong here
Incorrect. Phase 1 negotiation would show earlier errors.
✗
Preshared key mismatch.
Why it's wrong here
Incorrect. Preshared key mismatch causes authentication failure in Phase 1, not proposal error.
✓
IKE Phase 2 proposal mismatch.
Why this is correct
Correct. The warning explicitly states Phase 2 negotiation failed.
Related concept
Read the scenario before looking for a memorised answer.
✗
Invalid peer IP address.
Why it's wrong here
Incorrect. Invalid peer IP would prevent IKE initiation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Palo Alto Networks often tests the distinction between IKE Phase 1 and Phase 2 failures; the trap here is that candidates see an IPsec tunnel failure and immediately assume a preshared key or Phase 1 mismatch, without checking whether Phase 1 actually succeeded in the logs.
Trap categories for this question
Command / output trap
Incorrect. Phase 1 negotiation would show earlier errors.
Detailed technical explanation
How to think about this question
IKE Phase 2 (Quick Mode) negotiates the IPsec SA parameters, including the specific encryption and authentication algorithms for the data plane, as well as optional PFS (Perfect Forward Secrecy) using a Diffie-Hellman group. If the Phase 2 proposals do not match between peers, the responder will send a 'No Proposal Chosen' notification, and the initiator will log a Phase 2 failure. In real-world scenarios, this often occurs when one side is configured with PFS and the other is not, or when the PFS DH group differs.
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 — 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 Phase 2 proposal mismatch. — The log messages indicate that IKE Phase 1 completed successfully (as shown by the 'IKE Phase 1 established' message), but Phase 2 negotiation failed. This points directly to a mismatch in the IKE Phase 2 proposal parameters, such as the IPsec security protocol (ESP vs AH), encryption algorithm, authentication algorithm, or Diffie-Hellman group used for PFS. A Phase 2 proposal mismatch prevents the creation of the IPsec SA, even though the IKE SA is already established.
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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Question Discussion
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