This ANS-C01 practice question tests your understanding of network design. 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 wants to provide internet access to instances in a private subnet using a NAT gateway. The NAT gateway is deployed in a public subnet with an Elastic IP. The private subnet route table has a default route pointing to the NAT gateway. However, instances in the private subnet cannot access the internet. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The public subnet route table does not have a route to the internet gateway.
The NAT gateway is deployed in a public subnet, but for it to route traffic to the internet, the public subnet's route table must have a default route (0.0.0.0/0) pointing to an internet gateway (IGW). Without this route, the NAT gateway cannot forward traffic from the private subnet to the internet, even though the private subnet's route table correctly points to the NAT gateway. This is the most likely cause because the NAT gateway itself needs internet access via the IGW to translate and forward traffic.
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.
✓
The public subnet route table does not have a route to the internet gateway.
Why this is correct
NATgateway needs internet gateway route in its subnet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The security group assigned to the NAT gateway blocks outbound traffic.
Why it's wrong here
NATgateway security groups are not the primary cause.
✗
The private subnet route table has a route to the internet gateway instead of the NAT gateway.
Why it's wrong here
Private subnet route table should point to NATgateway, not internet gateway.
✗
The NAT gateway does not have an Elastic IP associated.
Why it's wrong here
Elastic IP is required and stated as present.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that a NATgateway automatically has internet access simply because it is in a public subnet, but the critical missing piece is the explicit route to the internet gateway in that subnet's route table.
Detailed technical explanation
How to think about this question
A NATgateway must reside in a public subnet with a route to an internet gateway to perform source network address translation (SNAT). When an instance in a private subnet sends traffic to the internet, the NAT gateway translates the source IP to its Elastic IP and forwards the packet; the return traffic must come back through the same NAT gateway, which requires the IGW route in the public subnet. Without this route, the NAT gateway cannot send or receive packets from the internet, effectively breaking the outbound connectivity for private instances.
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.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The public subnet route table does not have a route to the internet gateway. — The NAT gateway is deployed in a public subnet, but for it to route traffic to the internet, the public subnet's route table must have a default route (0.0.0.0/0) pointing to an internet gateway (IGW). Without this route, the NAT gateway cannot forward traffic from the private subnet to the internet, even though the private subnet's route table correctly points to the NAT gateway. This is the most likely cause because the NAT gateway itself needs internet access via the IGW to translate and forward traffic.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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