- A
The VPC does not have a default route (0.0.0.0/0) to the default internet gateway.
A default route is necessary for internet traffic to be sent to NAT.
- B
The firewall rules do not allow egress traffic.
Why wrong: Default egress allow-all rule exists, so this is less likely.
- C
The Cloud Router is in a different region.
Why wrong: NAT is regional; instances in same region as NAT should work.
- D
The instances are not assigned a network tag used by the NAT.
Why wrong: NAT applies to all instances in the region, no tag required.
Question 178 of 1,000
Google ACE Configuring Access and Security Practice Question
This ACE practice question tests your understanding of configuring access and 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 engineer is configuring a Cloud NAT to allow private Compute Engine instances to access the internet. After creating the Cloud Router and NAT gateway, the instances still cannot connect to the internet. What is the most likely missing configuration?
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 VPC does not have a default route (0.0.0.0/0) to the default internet gateway.
Cloud NAT requires that the subnet has Private Google Access enabled for certain Google APIs, but for general internet access, the instances must have a default route to the internet gateway (0.0.0.0/0 next hop to default internet gateway). If this route is missing, traffic won't be sent to NAT. The other options are possible but less common.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 VPC does not have a default route (0.0.0.0/0) to the default internet gateway.
Why this is correct
A default route is necessary for internet traffic to be sent to NAT.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The firewall rules do not allow egress traffic.
Why it's wrong here
Default egress allow-all rule exists, so this is less likely.
- ✗
The Cloud Router is in a different region.
Why it's wrong here
NAT is regional; instances in same region as NAT should work.
- ✗
The instances are not assigned a network tag used by the NAT.
Why it's wrong here
NAT applies to all instances in the region, no tag required.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ACE subnetting questions on CIDR, address ranges, and subnet selection.
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Configuring Access and Security — study guide chapter
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FAQ
Questions learners often ask
What does this ACE question test?
Configuring Access and Security — This question tests Configuring Access and Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The VPC does not have a default route (0.0.0.0/0) to the default internet gateway. — Cloud NAT requires that the subnet has Private Google Access enabled for certain Google APIs, but for general internet access, the instances must have a default route to the internet gateway (0.0.0.0/0 next hop to default internet gateway). If this route is missing, traffic won't be sent to NAT. The other options are possible but less common.
What should I do if I get this ACE question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ACE subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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Last reviewed: Jul 4, 2026
This ACE 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 ACE exam.
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