This PCNSE practice question tests your understanding of secure access and vpn. 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.
Exhibit
Refer to the exhibit.
CLI output:
admin@PA> show vpn ipsec tunnel name Corp-VPN
tunnel Corp-VPN: id 123, establishment status: initiator
Phase1: state UP, IKEv2
Phase2: state DOWN, reason: no matching proposal
What is the most likely cause of Phase2 being down?
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.
Exhibit
Refer to the exhibit.
CLI output:
admin@PA> show vpn ipsec tunnel name Corp-VPN
tunnel Corp-VPN: id 123, establishment status: initiator
Phase1: state UP, IKEv2
Phase2: state DOWN, reason: no matching proposal
A
Mismatched IKE version
Why wrong: IKE version mismatch causes Phase1 failure, not Phase2.
B
Mismatched IPSec encryption or authentication settings
'no matching proposal' indicates the IPsec proposal parameters do not match between peers.
C
Wrong tunnel interface IP address
Why wrong: Interface IP affects routing but not Phase2 negotiation.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Mismatched IPSec encryption or authentication settings
Phase 2 of an IPsecVPN 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.
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.
✗
Mismatched IKE version
Why it's wrong here
IKE version mismatch causes Phase1 failure, not Phase2.
✓
Mismatched IPSec encryption or authentication settings
Why this is correct
'no matching proposal' indicates the IPsec proposal parameters do not match between peers.
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.
✗
Wrong tunnel interface IP address
Why it's wrong here
Interface IP affects routing but not Phase2 negotiation.
✗
Incorrect pre-shared key
Why it's wrong here
Incorrect PSK causes Phase1 failure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Phase 1 and Phase 2 failures, incorrectly assuming that any mismatch in authentication or encryption settings (including pre-shared keys or IKE version) will cause Phase 2 to fail, when in fact those affect Phase 1, and only IPsec-specific transform set mismatches cause Phase 2 to be down while Phase 1 remains up.
Detailed technical explanation
How to think about this question
In IKEv1, Phase 2 (Quick Mode) negotiates IPsec SAs using the parameters defined in the crypto map or IKE gateway configuration, including transform sets that specify encryption (e.g., AES-CBC, 3DES), authentication (e.g., HMAC-SHA256, HMAC-MD5), and optional PFS (Perfect Forward Secrecy) DH groups. If PFS is enabled on one peer but not the other, or if the DH group for PFS mismatches, Phase 2 will fail even if all other settings match. On Palo Alto Networks firewalls, this is often seen in the system logs as 'Phase 2 negotiation failed' with a reason like 'proposal mismatch'.
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: Mismatched IPSec encryption or authentication settings — 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.
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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