- A
Configure a security group on the instances in the private subnet to allow outbound traffic only to the IP ranges of the AWS services.
Why wrong: IP ranges for AWS services can change and security groups cannot filter by service name.
- B
Use a NAT gateway in the public subnet and add a route to it in the private subnet.
Why wrong: A NAT gateway allows all outbound internet traffic, not just to specific services.
- C
Attach an internet gateway to the VPC and add a route to it in the private subnet.
Why wrong: This would give direct internet access to the private subnet, which is not desired.
- D
Create VPC endpoints for S3 and DynamoDB, and attach a policy to the endpoints to restrict access.
VPC endpoints provide private connectivity to AWS services and can be restricted with policies.
Quick Answer
The correct solution is to create VPC endpoints for S3 and DynamoDB and attach a policy to those endpoints to restrict access. This works because VPC endpoints allow instances in a private subnet to reach supported AWS services without traversing the internet, and endpoint policies act as a granular access control layer that can limit which specific buckets, tables, or actions are permitted. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how to restrict outbound traffic to AWS services VPC endpoints while avoiding common pitfalls like assuming a NAT gateway or internet gateway can filter by service—they cannot. A frequent trap is confusing security group rules with endpoint policies; remember that security groups filter by IP and port, not by AWS service. Memory tip: think of a VPC endpoint as a private tunnel with a bouncer (the policy) who only lets in guests with the right invitation.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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.
A company has a VPC with an internet gateway and wants to restrict outbound traffic from a private subnet to only allow traffic to specific AWS services, such as S3 and DynamoDB. Which solution should be used?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Create VPC endpoints for S3 and DynamoDB, and attach a policy to the endpoints to restrict access.
Option C is correct because VPC endpoints (Gateway or Interface) allow private subnet instances to access AWS services without traversing the internet, and they can be combined with bucket/endpoint policies to restrict access. Option A is incorrect because a NAT gateway allows all outbound traffic, not just to specific services. Option B is incorrect because security groups cannot filter by destination service. Option D is incorrect because an internet gateway would allow unrestricted outbound traffic.
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 a security group on the instances in the private subnet to allow outbound traffic only to the IP ranges of the AWS services.
Why it's wrong here
IP ranges for AWS services can change and security groups cannot filter by service name.
- ✗
Use a NAT gateway in the public subnet and add a route to it in the private subnet.
- ✗
Attach an internet gateway to the VPC and add a route to it in the private subnet.
Why it's wrong here
This would give direct internet access to the private subnet, which is not desired.
- ✓
Create VPC endpoints for S3 and DynamoDB, and attach a policy to the endpoints to restrict access.
Why this is correct
VPC endpoints provide private connectivity to AWS services and can be restricted with policies.
Related concept
CIDR notation defines the prefix length.
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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 VPC endpoints for S3 and DynamoDB, and attach a policy to the endpoints to restrict access. — Option C is correct because VPC endpoints (Gateway or Interface) allow private subnet instances to access AWS services without traversing the internet, and they can be combined with bucket/endpoint policies to restrict access. Option A is incorrect because a NAT gateway allows all outbound traffic, not just to specific services. Option B is incorrect because security groups cannot filter by destination service. Option D is incorrect because an internet gateway would allow unrestricted outbound traffic.
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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Last reviewed: Jun 20, 2026
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