The answer is to configure Cloud NAT with a static NAT IP address and ensure all traffic uses that IP. This is correct because Cloud NAT by default uses ephemeral IP addresses from a pool, which can change and break connections with external APIs that require a consistent source IP for security or logging purposes. By assigning a static NAT IP, you guarantee that every outbound packet from your private instances will have the same predictable source address, meeting the API’s static source IP requirement without exposing instances to the public internet. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of Cloud NAT’s address management and the distinction between ephemeral and static NAT IPs—a common trap is assuming you need to assign public IPs directly to instances. Remember the mnemonic: “Static NAT, consistent path—no IP flip, no API wrath.”
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing 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.
An organization has a Cloud NAT configured for a VPC network to allow outbound internet access for private instances. They notice that some instances are failing to connect to a specific external API that requires a static source IP. What should they do to resolve this?
Why wrong: Private Google Access is for Google APIs and services, not for external APIs.
B
Assign a static external IP to the instances and use Cloud NAT with static IPs.
Why wrong: Assigning static IPs to instances is possible but not the best approach; Cloud NAT with a static IP is simpler and provides a single egress IP.
C
Configure Cloud NAT with a static NAT IP address and ensure all traffic uses that IP.
This provides a consistent source IP for all outbound traffic, meeting the API's requirement.
D
Use a VPN tunnel to the API provider's network.
Why wrong: A VPN is complex and overkill; Cloud NAT with static IP is simpler.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure Cloud NAT with a static NAT IP address and ensure all traffic uses that IP.
Cloud NAT with a static NAT IP address ensures that all outbound traffic from private instances uses a consistent, predictable source IP. This satisfies the external API's requirement for a static source IP without needing to assign public IPs directly to instances. Option C correctly configures Cloud NAT to use a static IP, which is the intended solution for this scenario.
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.
✗
Use Private Google Access instead of Cloud NAT.
Why it's wrong here
Private Google Access is for Google APIs and services, not for external APIs.
✗
Assign a static external IP to the instances and use Cloud NAT with static IPs.
Why it's wrong here
Assigning static IPs to instances is possible but not the best approach; Cloud NAT with a static IP is simpler and provides a single egress IP.
✓
Configure Cloud NAT with a static NAT IP address and ensure all traffic uses that IP.
Why this is correct
This provides a consistent source IP for all outbound traffic, meeting the API's requirement.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a VPN tunnel to the API provider's network.
Why it's wrong here
A VPN is complex and overkill; Cloud NAT with static IP is simpler.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that assigning static external IPs to instances is necessary for static source IP requirements, when in fact Cloud NAT with a static IP achieves the same goal without compromising the private nature of the instances.
Detailed technical explanation
How to think about this question
Cloud NAT uses source network address translation (SNAT) to map private IPs to one or more public IP addresses. When configured with a static NAT IP, all outbound packets from the VPC are rewritten with that static IP, ensuring consistency even if instances are recreated or scaled. This is critical for APIs that whitelist source IPs, as dynamic NAT IPs would break connectivity after any change in the NAT gateway's external IP.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure Cloud NAT with a static NAT IP address and ensure all traffic uses that IP. — Cloud NAT with a static NAT IP address ensures that all outbound traffic from private instances uses a consistent, predictable source IP. This satisfies the external API's requirement for a static source IP without needing to assign public IPs directly to instances. Option C correctly configures Cloud NAT to use a static IP, which is the intended solution for this scenario.
What should I do if I get this PCNE 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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is using Cloud NAT for outbound internet access. They want to ensure that traffic from certain VMs always uses a specific set of NAT IPs for auditing purposes. Which three steps are necessary to achieve this? (Choose THREE.)
hard
✓ A.Ensure the VMs have a default route (0.0.0.0/0) with next hop set to the Cloud NAT gateway's subnet
B.Configure IAM conditions on the Cloud NAT resource to restrict which VMs can use it
C.Enable VPC Flow Logs on the subnet to monitor which NAT IPs are used
✓ D.Create a separate Cloud NAT gateway with the desired IPs and associate it with the VMs via a subnet or tags
✓ E.Configure VPC firewall rules to allow egress from the VMs to the internet
Why A: Option A is correct because for Cloud NAT to function, the VM must have a default route (0.0.0.0/0) that points to the Cloud NAT gateway's subnet as the next hop. Without this route, the VM's outbound traffic will not be directed to the NAT gateway, and the NAT IPs will not be used. This ensures that traffic from the VM is routed through the NAT gateway, allowing the specific set of NAT IPs to be applied for auditing.
Last reviewed: Jun 30, 2026
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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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