The answer is Identity-Aware Proxy (IAP) TCP forwarding, which enables secure SSH access to a Compute Engine instance that has no external IP address. IAP TCP forwarding works by establishing a secure tunnel through Google’s edge network, allowing you to connect to the instance using its internal IP without exposing it to the public internet. This is the recommended method because it eliminates the need for a public IP, bastion host, or VPN, while integrating with Cloud IAM for fine-grained access control. On the Google Professional Cloud Security Engineer exam, this question tests your understanding of secure remote access patterns and common misconfigurations—a frequent trap is confusing Cloud NAT (which only supports outbound traffic) with inbound SSH, or assuming firewall rules alone can reach an instance with no external IP. Remember the key distinction: IAP TCP forwarding is for inbound administrative access, while Cloud NAT is strictly for outbound internet. A simple memory tip: “IAP In, NAT Out.”
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 security engineer needs to provide secure SSH access to a Compute Engine instance that has no external IP address. What is the recommended method?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Identity-Aware Proxy (IAP) TCP forwarding.
Option B is correct because IAP TCP forwarding allows SSH without external IP. Option A is wrong because Cloud NAT is for outbound internet, not inbound SSH. Option C is wrong because VPC peering is for VPC-to-VPC, not for a single instance. Option D is wrong because firewall rules alone cannot provide access if there is no external IP.
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.
✗
Set up VPC peering with the instance's VPC.
Why it's wrong here
VPC peering allows connectivity between VPCs, but the instance still has no external IP and SSH would require a bastion host without IAP.
Without an external IP, traffic cannot reach the instance from the internet even with firewall rules.
✓
Use Identity-Aware Proxy (IAP) TCP forwarding.
Why this is correct
IAP TCP forwarding establishes an encrypted tunnel to the instance via the IAP service.
Related concept
Static NAT maps one inside address to one outside address.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 PCSE NAT questions on configuration and troubleshooting.
Configuring network security — This question tests Configuring network security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use Identity-Aware Proxy (IAP) TCP forwarding. — Option B is correct because IAP TCP forwarding allows SSH without external IP. Option A is wrong because Cloud NAT is for outbound internet, not inbound SSH. Option C is wrong because VPC peering is for VPC-to-VPC, not for a single instance. Option D is wrong because firewall rules alone cannot provide access if there is no external IP.
What should I do if I get this PCSE 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 PCSE NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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