- A
A NAT Gateway in a public subnet and a default route (0.0.0.0/0) in the private subnet's route table pointing to the NAT Gateway
This allows instances in private subnets to initiate outbound internet traffic through the NAT Gateway.
- B
A NAT instance in the private subnet with a route to an Internet Gateway
Why wrong: A NAT instance should be in a public subnet, not private.
- C
A VPC Gateway Endpoint for S3 in the private subnet
Why wrong: Gateway Endpoints only provide access to specific AWS services, not general internet.
- D
An Internet Gateway (IGW) attached to the VPC and a default route (0.0.0.0/0) in the private subnet's route table pointing to the IGW
Why wrong: Private subnets should not have a direct route to an IGW; that would make them public.
Question 1,352 of 1,705
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 has a VPC with public and private subnets. They launch an EC2 instance in a private subnet and need it to access the internet. Which combination of components is required?
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
✓
A NAT Gateway in a public subnet and a default route (0.0.0.0/0) in the private subnet's route table pointing to the NAT Gateway
A NAT Gateway in a public subnet provides outbound-only internet access for instances in private subnets. A default route (0.0.0.0/0) in the private subnet's route table pointing to the NAT Gateway ensures traffic destined for the internet is forwarded to the NAT Gateway, which then translates the source IP to its own Elastic IP and sends the traffic through the Internet Gateway (IGW) attached to the public subnet. This combination allows the EC2 instance to initiate outbound connections (e.g., for software updates) while remaining unreachable from the internet.
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.
- ✓
A NAT Gateway in a public subnet and a default route (0.0.0.0/0) in the private subnet's route table pointing to the NAT Gateway
- ✗
A NAT instance in the private subnet with a route to an Internet Gateway
Why it's wrong here
A NAT instance should be in a public subnet, not private.
- ✗
A VPC Gateway Endpoint for S3 in the private subnet
Why it's wrong here
Gateway Endpoints only provide access to specific AWS services, not general internet.
- ✗
An Internet Gateway (IGW) attached to the VPC and a default route (0.0.0.0/0) in the private subnet's route table pointing to the IGW
Why it's wrong here
Private subnets should not have a direct route to an IGW; that would make them public.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a NAT Gateway with a NAT instance, assuming both can be placed in any subnet, or they incorrectly think a default route to an IGW in a private subnet provides outbound-only access, not realizing the IGW enables bidirectional traffic and thus exposes the instance.
Detailed technical explanation
How to think about this question
NAT Gateway performs source network address translation (SNAT), replacing the private source IP with its own Elastic IP address, and tracks stateful connections so that return traffic is correctly forwarded back to the originating instance. Unlike a NAT instance, a NAT Gateway is managed by AWS, scales automatically up to 45 Gbps, and does not require patching or failover scripts. In a real-world scenario, if the private subnet route table mistakenly points to an IGW, the instance would receive a public IP (if auto-assigned) and become directly routable from the internet, breaking the isolation design.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: A NAT Gateway in a public subnet and a default route (0.0.0.0/0) in the private subnet's route table pointing to the NAT Gateway — A NAT Gateway in a public subnet provides outbound-only internet access for instances in private subnets. A default route (0.0.0.0/0) in the private subnet's route table pointing to the NAT Gateway ensures traffic destined for the internet is forwarded to the NAT Gateway, which then translates the source IP to its own Elastic IP and sends the traffic through the Internet Gateway (IGW) attached to the public subnet. This combination allows the EC2 instance to initiate outbound connections (e.g., for software updates) while remaining unreachable from the internet.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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