The answer is to create separate subnets in each Availability Zone for the application tier, deploy NAT gateways per AZ, and use an Application Load Balancer to distribute traffic across AZs. This design ensures that if one Availability Zone fails, the other zones continue serving traffic without a single point of failure, because each AZ has its own redundant resources and the load balancer automatically reroutes requests. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of fault isolation and resilient network architecture within a VPC multi-AZ high availability design. A common trap is assuming a single NAT gateway or a single public subnet spanning all AZs is sufficient, but subnets are inherently per-AZ and a single gateway creates a failure bottleneck. Remember the mnemonic: “Each AZ gets its own gate, so your app won’t meet its fate.”
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Which THREE of the following are considerations when designing a VPC with multiple Availability Zones for high availability? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use an Application Load Balancer to distribute traffic across instances in different Availability Zones.
Options B, D, and E are correct. Using NAT gateways in each AZ ensures availability if one AZ fails. Spreading subnets across AZs provides redundancy. Using an Application Load Balancer distributes traffic across AZs. Option A is wrong because a single NAT gateway in one AZ is a single point of failure. Option C is wrong because a single public subnet across all AZs is not possible; subnets are per AZ.
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.
✓
Use an Application Load Balancer to distribute traffic across instances in different Availability Zones.
Use a single NAT gateway in one Availability Zone to reduce cost.
Why it's wrong here
This creates a single point of failure.
Common exam traps
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 Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use an Application Load Balancer to distribute traffic across instances in different Availability Zones. — Options B, D, and E are correct. Using NAT gateways in each AZ ensures availability if one AZ fails. Spreading subnets across AZs provides redundancy. Using an Application Load Balancer distributes traffic across AZs. Option A is wrong because a single NAT gateway in one AZ is a single point of failure. Option C is wrong because a single public subnet across all AZs is not possible; subnets are per AZ.
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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