- A
The NAT gateway is not associated with a security group that allows outbound traffic.
Why wrong: Incorrect. NAT gateways do not require or support security groups. They rely on route tables and network ACLs.
- B
The NAT gateway's Elastic IP address is not properly allocated.
Why wrong: Incorrect. The NAT gateway has an Elastic IP assigned and is properly allocated. The Elastic IP being assigned does not cause the issue.
- C
The public subnet's route table does not have a route to an internet gateway.
Correct. The public subnet's route table must have a route to an internet gateway (IGW) for the NAT gateway to send traffic to the internet. Without this route, the NAT gateway is unable to forward packets from the private subnet to the internet.
- D
The private subnet's route table does not have a route to the NAT gateway.
Why wrong: Incorrect. The private subnet's route table already has a route to the NAT gateway (0.0.0.0/0 pointing to the NAT gateway), so this is not the problem.
Troubleshooting NAT Gateway: Ensure Public Subnet Has Internet Gateway Route
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. A key principle to apply: nAT Gateway. 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 has a VPC with an IPv4 CIDR block of 10.0.0.0/16. They have two subnets: a public subnet (10.0.1.0/24) and a private subnet (10.0.2.0/24). They launch an EC2 instance in the private subnet that needs to download software updates from the internet. The company configures a NAT gateway in the public subnet and adds a route in the private subnet's route table pointing 0.0.0.0/0 to the NAT gateway. The NAT gateway is assigned an Elastic IP address. However, the EC2 instance cannot reach the internet. The security group for the EC2 instance allows all outbound traffic. 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 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 public subnet's route table does not have a route to an internet gateway.
Option C is correct. The NAT gateway is in the public subnet, but the public subnet's route table must have a route to an internet gateway (0.0.0.0/0 -> IGW) for the NAT gateway to forward traffic to the internet. Without that route, the NAT gateway cannot communicate with the internet. Option A is incorrect because NAT gateways do not use security groups. Option B is incorrect because the NAT gateway has an Elastic IP and is properly allocated; the issue is not with the Elastic IP. Option D is incorrect because the private subnet's route table already has a route to the NAT gateway (0.0.0.0/0 -> NAT), which is correctly configured.
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 not associated with a security group that allows outbound traffic.
Why it's wrong here
Incorrect. NAT gateways do not require or support security groups. They rely on route tables and network ACLs.
- ✗
The NAT gateway's Elastic IP address is not properly allocated.
- ✓
The public subnet's route table does not have a route to an internet gateway.
Why this is correct
Correct. The public subnet's route table must have a route to an internet gateway (IGW) for the NAT gateway to send traffic to the internet. Without this route, the NAT gateway is unable to forward packets from the private subnet to the internet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
- ✗
The private subnet's route table does not have a route to the NAT gateway.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- NAT Gateway
- Internet Gateway (IGW)
- Route Table
- Public and Private Subnets
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
NAT Gateway
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 nAT Gateway, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — NAT Gateway.
What is the correct answer to this question?
The correct answer is: The public subnet's route table does not have a route to an internet gateway. — Option C is correct. The NAT gateway is in the public subnet, but the public subnet's route table must have a route to an internet gateway (0.0.0.0/0 -> IGW) for the NAT gateway to forward traffic to the internet. Without that route, the NAT gateway cannot communicate with the internet. Option A is incorrect because NAT gateways do not use security groups. Option B is incorrect because the NAT gateway has an Elastic IP and is properly allocated; the issue is not with the Elastic IP. Option D is incorrect because the private subnet's route table already has a route to the NAT gateway (0.0.0.0/0 -> NAT), which is correctly configured.
What should I do if I get this ANS-C01 question wrong?
Review nAT Gateway, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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?
NAT Gateway
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Last reviewed: Jun 20, 2026
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