- A
Security group on the instance with outbound rule allowing HTTPS
Why wrong: Security groups are stateful and automatically allow return traffic, but they do not filter by destination port in inbound. However, this is also valid, but NACL is more precise for this scenario. Typically, both are used. But the question might expect NACL because it's stateless. However, the security group approach is simpler. Given the options, A is more specific to the requirement of controlling subnet-level traffic.
- B
VPC gateway endpoint for S3
Why wrong: Gateway endpoints are for accessing S3 and DynamoDB, not for general internet access.
- C
Network ACL on the private subnet with outbound rule allowing HTTPS and inbound rule allowing return traffic
NACLs are stateless and require explicit inbound rules for return traffic.
- D
Security group on the NAT gateway with outbound rule allowing HTTPS
Why wrong: NAT gateways do not have security groups.
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 a public subnet and a private subnet. An EC2 instance in the private subnet needs to download patches from the internet. The instance is behind a NAT gateway in the public subnet. The security team wants to allow only outbound HTTPS traffic from the instance. Which configuration 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
Network ACL on the private subnet with outbound rule allowing HTTPS and inbound rule allowing return traffic
A NACL on the private subnet can control inbound and outbound traffic. For outbound HTTPS, allow outbound ephemeral ports and inbound port 443 for return traffic. Option B is wrong because security groups are stateful and automatically allow return traffic, but they do not filter by destination port in the inbound direction for stateful traffic. However, the question asks for a configuration that allows only outbound HTTPS; a security group with outbound rule for HTTPS works, but NACLs are also commonly used. But the best answer is NACL because it provides stateless filtering. Option C is wrong because the NAT gateway's security group (if it had one) would not apply to traffic from the private instance. Option D is wrong because VPC endpoints are for AWS services, not internet.
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.
- ✗
Security group on the instance with outbound rule allowing HTTPS
Why it's wrong here
Security groups are stateful and automatically allow return traffic, but they do not filter by destination port in inbound. However, this is also valid, but NACL is more precise for this scenario. Typically, both are used. But the question might expect NACL because it's stateless. However, the security group approach is simpler. Given the options, A is more specific to the requirement of controlling subnet-level traffic.
- ✗
VPC gateway endpoint for S3
Why it's wrong here
Gateway endpoints are for accessing S3 and DynamoDB, not for general internet access.
- ✓
Network ACL on the private subnet with outbound rule allowing HTTPS and inbound rule allowing return traffic
Why this is correct
NACLs are stateless and require explicit inbound rules for return traffic.
Related concept
CIDR notation defines the prefix length.
- ✗
Security group on the NAT gateway with outbound rule allowing HTTPS
Why it's wrong here
NAT gateways do not have security groups.
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.
Trap categories for this question
Scenario analysis trap
Security groups are stateful and automatically allow return traffic, but they do not filter by destination port in inbound. However, this is also valid, but NACL is more precise for this scenario. Typically, both are used. But the question might expect NACL because it's stateless. However, the security group approach is simpler. Given the options, A is more specific to the requirement of controlling subnet-level traffic.
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: Network ACL on the private subnet with outbound rule allowing HTTPS and inbound rule allowing return traffic — A NACL on the private subnet can control inbound and outbound traffic. For outbound HTTPS, allow outbound ephemeral ports and inbound port 443 for return traffic. Option B is wrong because security groups are stateful and automatically allow return traffic, but they do not filter by destination port in the inbound direction for stateful traffic. However, the question asks for a configuration that allows only outbound HTTPS; a security group with outbound rule for HTTPS works, but NACLs are also commonly used. But the best answer is NACL because it provides stateless filtering. Option C is wrong because the NAT gateway's security group (if it had one) would not apply to traffic from the private instance. Option D is wrong because VPC endpoints are for AWS services, not internet.
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
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.
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