The answer is to add a route for 0.0.0.0/0 pointing to the NAT gateway in the same Availability Zone within each private subnet’s route table. This configuration is correct because private subnets cannot use an Internet Gateway directly, and routing traffic to a NAT gateway in the same AZ ensures that traffic does not cross Availability Zone boundaries, which would introduce a single point of failure and potential data transfer costs. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of high-availability design for NAT gateways, specifically the requirement to configure NAT gateway routes for private subnets across AZs to maintain fault isolation. A common trap is selecting a single NAT gateway for all private subnets, which breaks availability if that AZ fails. Remember the memory tip: “Same AZ for the same way”—always pair a private subnet’s default route with the NAT gateway residing in its own Availability Zone.
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 using AWS CloudFormation to deploy a VPC with two public subnets and two private subnets across two Availability Zones. The template includes an internet gateway and a NAT gateway in each public subnet. The company needs to ensure that instances in the private subnets can access the internet. Which route table configuration should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a route 0.0.0.0/0 pointing to the NAT gateway in the same AZ in each private subnet route table.
Option D is correct because private subnets need a default route (0.0.0.0/0) pointing to a NAT gateway in the same AZ for high availability. A and B point to IGW which would not work for private subnets. C only points to one NAT gateway, not AZ-specific.
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.
✗
Add a route to the internet gateway in the private subnet route tables.
Why it's wrong here
Private subnets cannot have direct IGW routes.
✗
Add a route to the NAT gateway in the public subnet route tables.
Add a route 0.0.0.0/0 pointing to a single NAT gateway in both private subnet route tables.
Why it's wrong here
Single point of failure; best practice is one NAT per AZ.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: Add a route 0.0.0.0/0 pointing to the NAT gateway in the same AZ in each private subnet route table. — Option D is correct because private subnets need a default route (0.0.0.0/0) pointing to a NAT gateway in the same AZ for high availability. A and B point to IGW which would not work for private subnets. C only points to one NAT gateway, not AZ-specific.
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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