- A
A single NAT gateway in a public subnet, and a default route (0.0.0.0/0) in each private subnet route table pointing to that NAT gateway.
This provides centralized outbound internet access.
- B
A single NAT gateway in a private subnet, and a default route in each private subnet pointing to the NAT gateway.
Why wrong: NAT gateways must be in a public subnet.
- C
One NAT gateway per private subnet, each with a route to an internet gateway.
Why wrong: Multiple NAT gateways are not centrally managed.
- D
One NAT gateway per Availability Zone, with routes to the internet gateway.
Why wrong: Multiple NAT gateways are not centrally managed.
Question 291 of 1,748
NAT Gateway for Private Subnet Internet Access: Centralized Design
This SCS-C02 practice question tests your understanding of infrastructure security. 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 security engineer is designing a VPC with public and private subnets in two Availability Zones. The company requires that all outbound traffic from private subnets to the internet must go through a single, centrally managed NAT gateway. Which combination of resources and route table entries should be used?
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 single NAT gateway in a public subnet, and a default route (0.0.0.0/0) in each private subnet route table pointing to that NAT gateway.
Option A is correct because a single NAT gateway placed in a public subnet (with an Internet Gateway route) can be used by multiple private subnets across different Availability Zones. Each private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway's elastic network interface (ENI) or NAT Gateway ID, ensuring all outbound traffic from private instances is source-NATed through that single, centrally managed device.
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 single NAT gateway in a public subnet, and a default route (0.0.0.0/0) in each private subnet route table pointing to that NAT gateway.
Why this is correct
This provides centralized outbound internet access.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
A single NAT gateway in a private subnet, and a default route in each private subnet pointing to the NAT gateway.
Why it's wrong here
NAT gateways must be in a public subnet.
- ✗
One NAT gateway per private subnet, each with a route to an internet gateway.
Why it's wrong here
Multiple NAT gateways are not centrally managed.
- ✗
One NAT gateway per Availability Zone, with routes to the internet gateway.
Why it's wrong here
Multiple NAT gateways are not centrally managed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a NAT gateway must be in a private subnet because it handles private traffic, but AWS requires NAT gateways to be in a public subnet with an IGW route to function correctly.
Detailed technical explanation
How to think about this question
Under the hood, a NAT Gateway uses Source Network Address Translation (SNAT) to map private instance IPs to the NAT Gateway's Elastic IP (EIP) in the public subnet. The NAT Gateway's ENI must have a route to an Internet Gateway (IGW) via the public subnet's route table, while private subnet route tables point 0.0.0.0/0 to the NAT Gateway's ENI. A subtle behavior: if the NAT Gateway is in AZ-A and a private subnet in AZ-B uses it, traffic crosses AZ boundaries, incurring inter-AZ data transfer costs, which is acceptable for a single-NAT design but not for high availability.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A single NAT gateway in a public subnet, and a default route (0.0.0.0/0) in each private subnet route table pointing to that NAT gateway. — Option A is correct because a single NAT gateway placed in a public subnet (with an Internet Gateway route) can be used by multiple private subnets across different Availability Zones. Each private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway's elastic network interface (ENI) or NAT Gateway ID, ensuring all outbound traffic from private instances is source-NATed through that single, centrally managed device.
What should I do if I get this SCS-C02 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on SCS-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is designing a VPC with public and private subnets in two Availability Zones. They need to ensure that instances in the private subnets can access the internet for software updates but cannot be directly accessed from the internet. Which AWS service or feature should be used to meet this requirement?
medium- ✓ A.NAT Gateway
- B.VPC Peering
- C.AWS VPN
- D.Internet Gateway
Why A: A NAT Gateway enables instances in private subnets to initiate outbound traffic to the internet (e.g., for software updates) while preventing inbound traffic from the internet. An Internet Gateway (option D) would allow inbound traffic, which is not allowed. VPC Peering (option B) and AWS VPN (option C) do not provide internet access.
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Last reviewed: Jul 4, 2026
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