The correct answer is to deploy a NAT Gateway in each Availability Zone. This achieves NAT Gateway high availability by eliminating a single point of failure; if one AZ goes down, instances in the other private subnets retain internet access through their local NAT Gateway. Each private subnet’s route table must point to the NAT Gateway in its own AZ, ensuring traffic stays within the same Availability Zone for optimal latency and fault isolation. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of designing resilient, cost-effective VPC architectures—a common trap is assuming a single NAT Gateway or a NAT instance suffices, but the exam requires you to recognize that fully managed, AZ-specific gateways are the standard for production workloads. Remember the mnemonic: “One per AZ, routes stay local” to avoid the single-point-of-failure pitfall.
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 is designing a network for a VPC with a CIDR of 10.0.0.0/16. The VPC has three private subnets in three different Availability Zones. The company needs to provide internet access to instances in the private subnets for software updates. The architecture must be highly available and cost-effective. Which TWO actions should the network engineer take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure each private subnet's route table to route 0.0.0.0/0 to the NAT Gateway in the same Availability Zone.
To achieve high availability, deploy a NATGateway in each AZ. Each private subnet's route table should point to the NAT Gateway in its own AZ. Option A is correct because multiple NAT Gateways provide fault tolerance. Option D is correct because routing to the NAT Gateway in the same AZ ensures traffic stays within the AZ. Option B is incorrect because a single NAT Gateway is a single point of failure. Option C is incorrect because NAT instances are not fully managed and less reliable. Option E is incorrect because a single route table would force all traffic through one NAT Gateway.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Configure each private subnet's route table to route 0.0.0.0/0 to the NAT Gateway in the same Availability Zone.
Why this is correct
This ensures traffic uses the NATGateway in the same AZ.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure each private subnet's route table to route 0.0.0.0/0 to the NAT Gateway in the same Availability Zone. — To achieve high availability, deploy a NAT Gateway in each AZ. Each private subnet's route table should point to the NAT Gateway in its own AZ. Option A is correct because multiple NAT Gateways provide fault tolerance. Option D is correct because routing to the NAT Gateway in the same AZ ensures traffic stays within the AZ. Option B is incorrect because a single NAT Gateway is a single point of failure. Option C is incorrect because NAT instances are not fully managed and less reliable. Option E is incorrect because a single route table would force all traffic through one NAT Gateway.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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