IKE Version Mismatch — IPsec SA Stuck in Init State | Palo Alto Networks Certified Network Security Explained
This PCNSE practice question tests your understanding of secure access and vpn. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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
admin@PA-5000> show vpn ipsec-sa
Total IPsec SA: 3
Gateway: VPN-GW-1, Tunnel-id: 1, State: active, SPI: 123456, Encapsulation: tunnel
Gateway: VPN-GW-2, Tunnel-id: 2, State: init, SPI: 0, Encapsulation: tunnel
Gateway: VPN-GW-3, Tunnel-id: 3, State: active, SPI: 789012, Encapsulation: transport
Configuration for VPN-GW-2:
set network tunnel ipsec ipsec-crypto VPN-GW-2 ike-gateway VPN-GW-2-IKE
set network tunnel ipsec ipsec-crypto VPN-GW-2 esp-authentication sha1
set network tunnel ipsec ipsec-crypto VPN-GW-2 esp-encryption aes128
set network tunnel ipsec ipsec-crypto VPN-GW-2 lifetime 3600
set network ike gateway VPN-GW-2-IKE version ikev1
set network ike gateway VPN-GW-2-IKE protocol-version ikev1
set network ike gateway VPN-GW-2-IKE peer-address 10.1.1.1
set network ike gateway VPN-GW-2-IKE pre-shared-key mykey
set network ike gateway VPN-GW-2-IKE local-address 10.1.1.2
set network ike gateway VPN-GW-2-IKE local-id 10.1.1.2
set network ike gateway VPN-GW-2-IKE peer-id 10.1.1.1
set network tunnel ipsec ipsec-crypto VPN-GW-2 proxy-id local-ip 192.168.1.0/24
set network tunnel ipsec ipsec-crypto VPN-GW-2 proxy-id remote-ip 192.168.2.0/24
A site-to-site IPsec tunnel between two Palo Alto Networks firewalls is not passing traffic. The administrator runs the 'show vpn ipsec-sa' command and sees the output in the exhibit. The remote peer is configured to use IKEv2 only. Based on the configuration, what is the most likely cause of the tunnel being in 'init' state?
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
admin@PA-5000> show vpn ipsec-sa
Total IPsec SA: 3
Gateway: VPN-GW-1, Tunnel-id: 1, State: active, SPI: 123456, Encapsulation: tunnel
Gateway: VPN-GW-2, Tunnel-id: 2, State: init, SPI: 0, Encapsulation: tunnel
Gateway: VPN-GW-3, Tunnel-id: 3, State: active, SPI: 789012, Encapsulation: transport
Configuration for VPN-GW-2:
set network tunnel ipsec ipsec-crypto VPN-GW-2 ike-gateway VPN-GW-2-IKE
set network tunnel ipsec ipsec-crypto VPN-GW-2 esp-authentication sha1
set network tunnel ipsec ipsec-crypto VPN-GW-2 esp-encryption aes128
set network tunnel ipsec ipsec-crypto VPN-GW-2 lifetime 3600
set network ike gateway VPN-GW-2-IKE version ikev1
set network ike gateway VPN-GW-2-IKE protocol-version ikev1
set network ike gateway VPN-GW-2-IKE peer-address 10.1.1.1
set network ike gateway VPN-GW-2-IKE pre-shared-key mykey
set network ike gateway VPN-GW-2-IKE local-address 10.1.1.2
set network ike gateway VPN-GW-2-IKE local-id 10.1.1.2
set network ike gateway VPN-GW-2-IKE peer-id 10.1.1.1
set network tunnel ipsec ipsec-crypto VPN-GW-2 proxy-id local-ip 192.168.1.0/24
set network tunnel ipsec ipsec-crypto VPN-GW-2 proxy-id remote-ip 192.168.2.0/24
A
The IKE version is incompatible.
Local uses IKEv1, remote expects IKEv2; Phase 1 negotiation fails, resulting in 'init' state.
B
The pre-shared key is incorrect.
Why wrong: An incorrect PSK would cause IKE authentication failure, but the remote peer's IKE version is explicitly stated as IKEv2 only, making this less likely.
C
The proxy IDs are mismatched with the peer.
Why wrong: Proxy ID mismatch causes Phase 2 failure, not Phase 1; the tunnel would show 'active' for Phase 1.
D
The IPsec crypto profile lifetime is too short.
Why wrong: Lifetime settings affect re-keying, not initial SA establishment.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IKE version is incompatible.
The 'init' state in the 'show vpnipsec-sa' output indicates that the IPsec Security Association (SA) has not been established because the IKE phase 1 negotiation failed. Since the remote peer is configured to use IKEv2 only, and the local firewall is likely configured for IKEv1 (or both, but not matching), the IKE version mismatch prevents the initial key exchange. This is the most direct cause of the tunnel remaining in 'init' state.
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.
✓
The IKE version is incompatible.
Why this is correct
Local uses IKEv1, remote expects IKEv2; Phase 1 negotiation fails, resulting in 'init' state.
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.
✗
The pre-shared key is incorrect.
Why it's wrong here
An incorrect PSK would cause IKE authentication failure, but the remote peer's IKE version is explicitly stated as IKEv2 only, making this less likely.
✗
The proxy IDs are mismatched with the peer.
Why it's wrong here
Proxy ID mismatch causes Phase 2 failure, not Phase 1; the tunnel would show 'active' for Phase 1.
✗
The IPsec crypto profile lifetime is too short.
Why it's wrong here
Lifetime settings affect re-keying, not initial SA establishment.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume 'init' state always indicates a pre-shared key mismatch or proxy ID issue, but in this scenario the IKE version mismatch is the root cause because the tunnel never progresses past the initial IKE exchange.
Trap categories for this question
Command / output trap
Proxy ID mismatch causes Phase 2 failure, not Phase 1; the tunnel would show 'active' for Phase 1.
Detailed technical explanation
How to think about this question
IKEv1 and IKEv2 use different message formats, exchange sequences, and SA payload structures (e.g., IKEv2 uses a single exchange with two messages for phase 1, while IKEv1 uses six messages in main mode). On Palo Alto Networks firewalls, the IKE gateway configuration includes an 'IKE version' setting (v1-only, v2-only, or v1/v2); if the local firewall is set to v1-only and the remote peer is v2-only, the initiator sends an IKE_SA_INIT request that the responder cannot parse, resulting in no response and the SA staying in 'init'. This is a common misconfiguration when migrating from IKEv1 to IKEv2.
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: The IKE version is incompatible. — The 'init' state in the 'show vpn ipsec-sa' output indicates that the IPsec Security Association (SA) has not been established because the IKE phase 1 negotiation failed. Since the remote peer is configured to use IKEv2 only, and the local firewall is likely configured for IKEv1 (or both, but not matching), the IKE version mismatch prevents the initial key exchange. This is the most direct cause of the tunnel remaining in 'init' state.
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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