- A
Deploy a NAT gateway in each public subnet and configure private route tables with a default route to the NAT gateway in the same AZ.
Provides high availability (each AZ independent) and uses managed service, cost-effective for moderate traffic.
- B
Create a single NAT gateway in one public subnet and route all private traffic to it.
Why wrong: Single point of failure; if that AZ fails, private instances lose internet access.
- C
Attach an internet gateway to the VPC and add a default route to it in the private subnets.
Why wrong: Private subnets need a NAT device, not direct internet gateway access.
- D
Launch a NAT instance in each public subnet and configure the private route tables.
Why wrong: NAT instances require manual scaling and patching, less reliable than managed NAT gateways.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 are used for NAT gateways and an Application Load Balancer (ALB). The private subnets host EC2 instances running a web application. What is the most cost-effective and highly available configuration for internet access from the private instances?
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
Deploy a NAT gateway in each public subnet and configure private route tables with a default route to the NAT gateway in the same AZ.
Option A is correct because deploying a NAT gateway in each public subnet (one per Availability Zone) ensures that private instances in each AZ can route outbound traffic through a NAT gateway in the same AZ, providing both high availability (no single point of failure) and cost efficiency (no cross-AZ data transfer charges). This configuration uses the default route (0.0.0.0/0) in the private route tables pointing to the NAT gateway in the same AZ, which avoids the per-GB data transfer costs that would occur if traffic crossed AZs to reach a single NAT gateway.
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.
- ✓
Deploy a NAT gateway in each public subnet and configure private route tables with a default route to the NAT gateway in the same AZ.
Why this is correct
Provides high availability (each AZ independent) and uses managed service, cost-effective for moderate traffic.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a single NAT gateway in one public subnet and route all private traffic to it.
Why it's wrong here
Single point of failure; if that AZ fails, private instances lose internet access.
- ✗
Attach an internet gateway to the VPC and add a default route to it in the private subnets.
- ✗
Launch a NAT instance in each public subnet and configure the private route tables.
Why it's wrong here
NAT instances require manual scaling and patching, less reliable than managed NAT gateways.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that a single NAT gateway is sufficient for high availability, but the trap here is that a single NAT gateway is a single point of failure and incurs cross-AZ data transfer costs, making per-AZ NAT gateways the correct cost-effective and highly available design.
Detailed technical explanation
How to think about this question
NAT gateways are managed by AWS and automatically scale up to 45 Gbps, while NAT instances are EC2 instances with limited throughput (e.g., 1-5 Gbps depending on instance type). The cross-AZ data transfer charge is $0.01 per GB in each direction, so a single NAT gateway in AZ-a serving instances in AZ-b would incur $0.02 per GB (in + out), making a per-AZ NAT gateway more cost-effective for high-traffic workloads. Additionally, NAT gateways are highly available within an AZ (they are deployed across multiple redundant devices), but they are not resilient to AZ failures, so one per AZ is required for full 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
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy a NAT gateway in each public subnet and configure private route tables with a default route to the NAT gateway in the same AZ. — Option A is correct because deploying a NAT gateway in each public subnet (one per Availability Zone) ensures that private instances in each AZ can route outbound traffic through a NAT gateway in the same AZ, providing both high availability (no single point of failure) and cost efficiency (no cross-AZ data transfer charges). This configuration uses the default route (0.0.0.0/0) in the private route tables pointing to the NAT gateway in the same AZ, which avoids the per-GB data transfer costs that would occur if traffic crossed AZs to reach a single NAT gateway.
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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