The answer is a NAT Gateway in each public subnet, with a route in the private route tables pointing to the NAT Gateway. This combination provides reliable outbound internet access for private subnet EC2 instances needing software updates while blocking any inbound connections from the internet, because the NAT Gateway operates at the network layer, translating private IPs to the public IP of the gateway and dropping unsolicited inbound traffic. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of high-availability design for outbound-only connectivity—the key trap is confusing a NAT Gateway with a NAT instance, which requires manual patching and failover management, or assuming an Internet Gateway alone can provide private access without exposing instances. The exam emphasizes operational overhead reduction, so remember that managed services like NAT Gateways are preferred over self-managed instances. Memory tip: “NAT Gateway is the set-and-forget bridge—private out, no public in.”
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 has a VPC with public and private subnets in two Availability Zones. The private subnets host EC2 instances that need to access the internet for software updates but must not be accessible from the internet. Which combination of resources meets these requirements with the least operational overhead?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A NAT Gateway in each public subnet, with a route in the private route tables pointing to the NAT Gateway
A NATGateway in a public subnet provides outbound internet access for private instances while preventing inbound access. Option A is correct. Option B (NAT instance) requires management. Option C (VPC endpoint) is for specific AWS services, not general internet. Option D (Internet Gateway directly) would make instances publicly accessible.
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.
✗
A VPC endpoint for Amazon S3 in each private subnet
Why it's wrong here
VPC endpoints only provide access to specific AWS services, not general internet.
✓
A NAT Gateway in each public subnet, with a route in the private route tables pointing to the NAT Gateway
Why this is correct
NATGateway is managed and provides outbound internet access.
Clue confirmation
The clue word "least" in the question point toward this answer.
A NAT instance in each public subnet, with a route in the private route tables pointing to the NAT instance
Why it's wrong here
NAT instances require manual patching and management.
✗
An Internet Gateway attached to the VPC with a route in the private route tables pointing to the Internet Gateway
Why it's wrong here
An Internet Gateway alone would not allow private instances to access the internet; they need a NAT device.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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: A NAT Gateway in each public subnet, with a route in the private route tables pointing to the NAT Gateway — A NAT Gateway in a public subnet provides outbound internet access for private instances while preventing inbound access. Option A is correct. Option B (NAT instance) requires management. Option C (VPC endpoint) is for specific AWS services, not general internet. Option D (Internet Gateway directly) would make instances publicly accessible.
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.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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 →
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. The private subnets host databases that must be accessible only from the application servers in the public subnets. Which VPC feature should be used to allow the application servers to access the databases while preventing direct internet access to the databases?
easy
A.Create a VPC Peering connection between the public and private subnets.
✓ B.Attach a NAT Gateway in a public subnet and update the route table of the private subnets to point to the NAT Gateway for outbound traffic.
C.Attach an Internet Gateway to the VPC and update the route table of the private subnets to point to the Internet Gateway.
D.Attach a Virtual Private Gateway to the VPC and update the route table of the private subnets.
Why B: Option B is correct because a NAT Gateway allows instances in private subnets to initiate outbound traffic to the internet, but it does not allow inbound traffic from the internet, which aligns with the requirement. Option A is wrong because an Internet Gateway would allow inbound traffic from the internet. Option C is wrong because a VPC Peering connection is used for connecting VPCs. Option D is wrong because a Virtual Private Gateway is used for VPN connections.
Variation 2. A company has a VPC with public and private subnets in two Availability Zones. The private subnets host EC2 instances that need to access the internet for software updates. The company must ensure that traffic from the private instances uses a single, predictable public IP address. What is the MOST cost-effective solution?
medium
A.Attach an Internet Gateway to the VPC and update the private subnet route table with a default route to the Internet Gateway.
B.Create a Transit Gateway with a VPC attachment and route traffic through a central egress VPC.
✓ C.Deploy a NAT Gateway in a public subnet in one Availability Zone, and route private subnet traffic to it.
D.Launch a NAT instance in a public subnet and configure source/destination check.
Why C: Option C is correct because a NAT Gateway in a public subnet provides outbound-only internet access for private instances, and it uses a single Elastic IP address, ensuring a predictable public IP. This is the most cost-effective managed solution, as NAT Gateways are highly available within an Availability Zone and require no manual instance management.
Variation 3. A company has a VPC with public and private subnets in two Availability Zones. The private subnets need to access the internet for software updates. Which configuration meets this requirement securely?
easy
✓ A.Deploy a NAT Gateway in a public subnet and update the private subnet route tables to point 0.0.0.0/0 to the NAT Gateway.
B.Attach an Internet Gateway to the VPC and add a route to 0.0.0.0/0 in the private subnet route tables pointing to the Internet Gateway.
C.Create a VPC Peering connection to a second VPC that has an Internet Gateway and route all traffic through it.
D.Configure a Virtual Private Gateway and use an AWS Direct Connect connection to the internet.
Why A: Option A is correct because a NAT Gateway in a public subnet allows private instances to initiate outbound traffic to the internet. Option B is wrong because an Internet Gateway does not allow private instances to reach the internet. Option C is wrong because a VPC Peering connection does not provide internet access. Option D is wrong because a Virtual Private Gateway is used for VPN connections.
Variation 4. A company has a VPC with public and private subnets in three Availability Zones. The company hosts a web application on Amazon EC2 instances in the private subnets. The instances need to download security patches from the internet but must not be directly accessible from the internet. Which solution meets these requirements with the least operational overhead?
easy
A.Deploy a NAT instance in a public subnet and configure the private subnet route tables to point to the NAT instance.
B.Attach an internet gateway to the VPC and add a default route to the internet gateway in the private subnet route tables.
C.Create a VPC endpoint for Amazon S3 and configure the instances to use the endpoint.
✓ D.Deploy a NAT gateway in each public subnet and configure the private subnet route tables to point to the respective NAT gateway.
Why D: Option D is correct because a NAT gateway is a fully managed AWS service that provides outbound internet connectivity for instances in private subnets while preventing inbound internet access. Deploying a NAT gateway in each public subnet across three Availability Zones ensures high availability and fault tolerance, and configuring private subnet route tables with a default route (0.0.0.0/0) pointing to the respective NAT gateway meets the requirement with minimal operational overhead, as AWS handles patching and scaling.
Variation 5. A company has a VPC with public and private subnets in three Availability Zones. They want to provide outbound internet access to instances in private subnets while preventing inbound traffic from the internet. Which solution meets these requirements with the least operational overhead?
medium
A.Deploy a NAT instance in a public subnet and configure the private subnet route table to point to it.
B.Attach an Internet Gateway to the VPC and add a default route to it in the private subnet route table.
✓ C.Create a NAT Gateway in a public subnet and add a default route in the private subnet route table pointing to the NAT Gateway.
D.Create a VPC Gateway Endpoint for Amazon S3 and route outbound traffic through it.
Why C: Option C is correct because a NAT Gateway is a fully managed AWS service that provides outbound internet access for instances in private subnets while blocking unsolicited inbound connections. By placing the NAT Gateway in a public subnet and adding a default route (0.0.0.0/0) in the private subnet route table pointing to the NAT Gateway, traffic from private instances is source NATed to the NAT Gateway's Elastic IP, ensuring inbound traffic from the internet cannot reach the private instances. This solution offers the least operational overhead as AWS handles scaling, patching, and availability, unlike a self-managed NAT instance.
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