- A
The encryption algorithm (e.g., AES256) or DH group (e.g., 14) does not match between the two ends.
This is the classic cause of 'no proposal chosen' – the parameters for the IKE SA do not match.
- B
The on-premises device is behind NAT and the VPN gateway does not support NAT traversal.
Why wrong: NAT traversal issues would cause timeout or no response, not this specific error.
- C
The IKE version on the on-premises device is set to IKEv1 while Cloud VPN expects IKEv2.
Why wrong: Cloud VPN supports IKEv1 and IKEv2, but if you explicitly set IKEv2, version mismatch would cause a different error.
- D
The pre-shared keys on both ends are different.
Why wrong: PSK mismatch would cause authentication failure, not proposal mismatch.
Question 174 of 1,000
PCNE Implementing Hybrid Interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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.
A network engineer is configuring an HA VPN tunnel pair between an on-premises VPN device and Google Cloud. The engineer wants to use IKEv2 with pre-shared keys. After configuring both ends, the tunnels do not come up. The engineer sees 'IKE SA negotiation failed - no proposal chosen' in the logs. What is the most likely cause?
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.
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
✓
The encryption algorithm (e.g., AES256) or DH group (e.g., 14) does not match between the two ends.
This error typically indicates a mismatch in IKE proposal parameters such as encryption algorithm, integrity algorithm, DH group, or SA lifetime.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 encryption algorithm (e.g., AES256) or DH group (e.g., 14) does not match between the two ends.
Why this is correct
This is the classic cause of 'no proposal chosen' – the parameters for the IKE SA do not match.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The on-premises device is behind NAT and the VPN gateway does not support NAT traversal.
Why it's wrong here
NAT traversal issues would cause timeout or no response, not this specific error.
- ✗
The IKE version on the on-premises device is set to IKEv1 while Cloud VPN expects IKEv2.
Why it's wrong here
Cloud VPN supports IKEv1 and IKEv2, but if you explicitly set IKEv2, version mismatch would cause a different error.
- ✗
The pre-shared keys on both ends are different.
Why it's wrong here
PSK mismatch would cause authentication failure, not proposal mismatch.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNE NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing Hybrid Interconnectivity — This question tests Implementing Hybrid Interconnectivity — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The encryption algorithm (e.g., AES256) or DH group (e.g., 14) does not match between the two ends. — This error typically indicates a mismatch in IKE proposal parameters such as encryption algorithm, integrity algorithm, DH group, or SA lifetime.
What should I do if I get this PCNE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNE NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jul 4, 2026
This PCNE practice question is part of Courseiva's free Google Cloud 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 PCNE exam.
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