- A
Create a security group for the database that allows inbound from the on-premises network using a prefix list for 203.0.113.0/24. Create a VPC endpoint for S3 and allow outbound traffic to the endpoint. Keep the private subnet's network ACL default (allow all outbound).
Why wrong: Security groups do not support prefix lists for inbound rules from on-premises CIDRs; they only support CIDR blocks or security group IDs. Also, allowing all outbound traffic in the network ACL is not restrictive enough.
- B
Set up a Site-to-Site VPN between the on-premises network and the VPC. Modify the route tables to route 203.0.113.0/24 through the VPN. Place the database in a private subnet and allow inbound from the VPN CIDR. Use an internet gateway for outbound traffic to S3.
Why wrong: A VPN is overkill for a single IP range and adds complexity. Using an internet gateway for outbound traffic to S3 is not recommended; a VPC endpoint is more secure and cost-effective.
- C
Modify the database security group to allow inbound TCP 3306 from 203.0.113.0/24. Create a VPC endpoint for S3. Update the private subnet's network ACL to deny all outbound traffic except to the S3 VPC endpoint prefix list.
This directly permits the required on-premises access and restricts outbound traffic to only S3 via VPC endpoint, which is secure and efficient.
- D
Place the database in a public subnet and use a security group that allows inbound from 203.0.113.0/24. Use the NAT gateway for outbound traffic to S3. Configure the public subnet's network ACL to deny all outbound traffic except to S3.
Why wrong: Placing the database in a public subnet exposes it to the internet unnecessarily. The NAT gateway is not needed for on-premises access; also, network ACLs are stateless and require symmetric rules.
ANS-C01 Security Group 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. A key principle to apply: security Group. 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 Amazon VPC with a public subnet and a private subnet. The public subnet has a NAT gateway. The private subnet has an Amazon RDS for MySQL database. The security team wants to ensure that the database is not accessible from the internet, but they need to allow a specific on-premises network (IP range 203.0.113.0/24) to connect to the database for maintenance. The company also wants to restrict outbound traffic from the database to only necessary AWS services (e.g., S3 for backups) and deny all other outbound traffic. Which configuration should the security team implement?
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
Modify the database security group to allow inbound TCP 3306 from 203.0.113.0/24. Create a VPC endpoint for S3. Update the private subnet's network ACL to deny all outbound traffic except to the S3 VPC endpoint prefix list.
The correct answer is C. This configuration allows inbound access from the specific on-premises CIDR (203.0.113.0/24) directly via the database security group, which is secure and avoids the complexity of a VPN. Creating a VPC endpoint for S3 enables private connectivity to S3 without traversing the internet. Updating the private subnet's network ACL to deny all outbound traffic except to the S3 VPC endpoint prefix list restricts outbound traffic as required. Option A is incorrect because a security group cannot reference a prefix list for on-premises IPs; prefix lists are used for AWS services or specific VPC resources. Option B is incorrect because a Site-to-Site VPN adds unnecessary complexity for a single on-premises CIDR, and using an internet gateway for outbound traffic to S3 bypasses the requirement to restrict outbound traffic. Option D is incorrect because placing the database in a public subnet would expose it to the internet, and using a NAT gateway for outbound traffic to S3 is not as secure as a VPC endpoint.
Key principle: Security Group
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a security group for the database that allows inbound from the on-premises network using a prefix list for 203.0.113.0/24. Create a VPC endpoint for S3 and allow outbound traffic to the endpoint. Keep the private subnet's network ACL default (allow all outbound).
- ✗
Set up a Site-to-Site VPN between the on-premises network and the VPC. Modify the route tables to route 203.0.113.0/24 through the VPN. Place the database in a private subnet and allow inbound from the VPN CIDR. Use an internet gateway for outbound traffic to S3.
- ✓
Modify the database security group to allow inbound TCP 3306 from 203.0.113.0/24. Create a VPC endpoint for S3. Update the private subnet's network ACL to deny all outbound traffic except to the S3 VPC endpoint prefix list.
Why this is correct
This directly permits the required on-premises access and restricts outbound traffic to only S3 via VPC endpoint, which is secure and efficient.
Related concept
Security Group
- ✗
Place the database in a public subnet and use a security group that allows inbound from 203.0.113.0/24. Use the NAT gateway for outbound traffic to S3. Configure the public subnet's network ACL to deny all outbound traffic except to S3.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is to assume that a VPN is required for on-premises access, but a direct security group rule with the on-premises CIDR is simpler and sufficient. Also, confusing network ACLs with security groups: security groups are stateful and allow return traffic automatically, while network ACLs are stateless and require explicit rules for return traffic.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Security Group
- Network ACL
- VPC Endpoint
- Prefix List
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Security Group
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.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
What to study next
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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 — Security Group.
What is the correct answer to this question?
The correct answer is: Modify the database security group to allow inbound TCP 3306 from 203.0.113.0/24. Create a VPC endpoint for S3. Update the private subnet's network ACL to deny all outbound traffic except to the S3 VPC endpoint prefix list. — The correct answer is C. This configuration allows inbound access from the specific on-premises CIDR (203.0.113.0/24) directly via the database security group, which is secure and avoids the complexity of a VPN. Creating a VPC endpoint for S3 enables private connectivity to S3 without traversing the internet. Updating the private subnet's network ACL to deny all outbound traffic except to the S3 VPC endpoint prefix list restricts outbound traffic as required. Option A is incorrect because a security group cannot reference a prefix list for on-premises IPs; prefix lists are used for AWS services or specific VPC resources. Option B is incorrect because a Site-to-Site VPN adds unnecessary complexity for a single on-premises CIDR, and using an internet gateway for outbound traffic to S3 bypasses the requirement to restrict outbound traffic. Option D is incorrect because placing the database in a public subnet would expose it to the internet, and using a NAT gateway for outbound traffic to S3 is not as secure as a VPC endpoint.
What should I do if I get this ANS-C01 question wrong?
Review security Group, then practise related ANS-C01 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Security Group
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Last reviewed: Jun 20, 2026
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