- A
The NAT gateway is placed in a private subnet and does not have a route to the internet gateway.
NAT gateways must reside in a public subnet with a route to an internet gateway. If placed in a private subnet, outbound traffic cannot reach the internet.
- B
The route table for the private subnets is not associated with the VPC's main route table.
Why wrong: Route table association is per subnet, not per VPC, and the main route table is used by default. Missing association would affect connectivity but is less likely than a misconfigured NAT gateway.
- C
The private subnets have a default route (0.0.0.0/0) pointing to an internet gateway instead of the NAT gateway.
Why wrong: This would cause traffic to go directly to the internet gateway, but the private instances would still not have a return path because they lack public IPs. However, the issue is more likely a misconfiguration of the NAT gateway itself.
- D
The public subnets have a default route pointing to the NAT gateway instead of the internet gateway.
Why wrong: Public subnets should have a default route to the internet gateway, not NAT gateway. This misconfiguration would break internet access for instances in public subnets, not private ones.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 company is deploying a VPC with public and private subnets in two Availability Zones. The public subnets contain NAT gateways for outbound internet access from the private subnets. The private subnets host web servers that need to make API calls to an external service over the internet. After implementation, the web servers cannot reach the internet. Which configuration 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 NAT gateway is placed in a private subnet and does not have a route to the internet gateway.
Option B is correct because each NAT gateway must be in a public subnet with a route to an internet gateway. If the NAT gateway is in a private subnet, it cannot route traffic to the internet. Option A is incorrect because private subnets do not need default routes to the internet gateway. Option C is incorrect because route propagation is not required. Option D is incorrect because NAT gateway is not a required check for public subnets.
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 NAT gateway is placed in a private subnet and does not have a route to the internet gateway.
Why this is correct
NAT gateways must reside in a public subnet with a route to an internet gateway. If placed in a private subnet, outbound traffic cannot reach the internet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The route table for the private subnets is not associated with the VPC's main route table.
- ✗
The private subnets have a default route (0.0.0.0/0) pointing to an internet gateway instead of the NAT gateway.
- ✗
The public subnets have a default route pointing to the NAT gateway instead of the internet gateway.
Why it's wrong here
Public subnets should have a default route to the internet gateway, not NAT gateway. This misconfiguration would break internet access for instances in public subnets, not private ones.
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.
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The NAT gateway is placed in a private subnet and does not have a route to the internet gateway. — Option B is correct because each NAT gateway must be in a public subnet with a route to an internet gateway. If the NAT gateway is in a private subnet, it cannot route traffic to the internet. Option A is incorrect because private subnets do not need default routes to the internet gateway. Option C is incorrect because route propagation is not required. Option D is incorrect because NAT gateway is not a required check for public subnets.
What should I do if I get this ANS-C01 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 ANS-C01 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: Jun 20, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.
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