The answer is to create a VPC endpoint for Amazon S3 and add a route to that endpoint in the private subnet route table. This configuration is correct because a Gateway VPC endpoint allows instances in private subnets to communicate with S3 over the AWS network, bypassing the internet entirely, which satisfies the requirement to block all outbound internet traffic except for S3. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of granular network control versus broad solutions like NAT gateways, which would permit all outbound internet traffic and fail the security constraint. A common trap is assuming a NAT gateway or proxy is needed, but those introduce unnecessary internet egress; the key insight is that S3’s Gateway endpoint is free and operates at the route table level. Memory tip: think “S3 Gateway = no internet gateway needed” — if the goal is to block the internet, a NAT gateway is the wrong tool.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 has a VPC with public and private subnets. The security team wants to block all outbound traffic to the internet from the private subnets except for traffic to an AWS service like Amazon S3. Which 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
✓
Create a VPC endpoint for Amazon S3 and add a route to the endpoint in the private subnet route table.
A VPC endpoint for S3 allows private subnet instances to access S3 without going through an internet gateway. A NAT gateway would allow all internet traffic, not just S3. A proxy server would allow all traffic unless configured to restrict. Internet gateway alone does not provide granular control.
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.
✗
Attach an internet gateway to the VPC and add a route to the internet gateway in the private subnet route table.
Why it's wrong here
Internet gateway would allow all outbound traffic, not just S3.
✓
Create a VPC endpoint for Amazon S3 and add a route to the endpoint in the private subnet route table.
Why this is correct
VPC endpoint provides private connectivity to S3 without internet access.
Place a proxy server in the private subnet and configure all instances to use it.
Why it's wrong here
Proxy server would allow all traffic unless explicitly restricted.
✗
Configure a NAT gateway in the public subnet and update the route table to send 0.0.0.0/0 traffic to the NAT gateway.
Why it's wrong here
NATgateway allows all outbound traffic, not just to S3.
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 Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a VPC endpoint for Amazon S3 and add a route to the endpoint in the private subnet route table. — A VPC endpoint for S3 allows private subnet instances to access S3 without going through an internet gateway. A NAT gateway would allow all internet traffic, not just S3. A proxy server would allow all traffic unless configured to restrict. Internet gateway alone does not provide granular control.
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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This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
Question Discussion
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