The answer is AWS Network Firewall, as it is the only AWS service that provides dedicated, managed stateful firewall for VPC subnet traffic inspection while meeting PCI DSS compliance requirements. Unlike security groups, which are stateful but operate as simple instance-level rules rather than a full inspection appliance, AWS Network Firewall performs deep packet inspection across all traffic between subnets, scales automatically to handle varying workloads, and is deployed across multiple Availability Zones for high availability. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your ability to distinguish between stateful and stateless inspection services, with a common trap being to confuse security groups’ statefulness with the need for a centralized firewall appliance—remember that security groups lack the logging, intrusion prevention, and centralized policy management required for compliance frameworks like PCI DSS. A useful memory tip: think of AWS Network Firewall as the “stateful gatekeeper” for VPC traffic, while security groups are just “stateful bouncers” for individual instances.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 security team is designing a network architecture that must meet PCI DSS compliance. They have a VPC with multiple subnets and need to ensure that all traffic between subnets is inspected by a stateful firewall. The solution must also support scalability and high availability. Which AWS service should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AWS Network Firewall
Option B is correct. AWS Network Firewall provides stateful inspection, scales automatically, and is highly available. Option A is wrong because security groups are stateless? Actually, security groups are stateful, but they are not a firewall appliance for inspection; they are simple rules. Option C is wrong because Network ACLs are stateless. Option D is wrong because AWS WAF is for web application layer, not network layer.
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.
✓
AWS Network Firewall
Why this is correct
Provides stateful network inspection, scales, and is highly available.
Security groups are stateful but not designed for centralized inspection and cannot inspect all traffic.
✗
AWS WAF
Why it's wrong here
WAF is for web application layer, not network layer inspection.
✗
Network ACLs on each subnet
Why it's wrong here
Network ACLs are stateless and do not provide deep packet inspection.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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: AWS Network Firewall — Option B is correct. AWS Network Firewall provides stateful inspection, scales automatically, and is highly available. Option A is wrong because security groups are stateless? Actually, security groups are stateful, but they are not a firewall appliance for inspection; they are simple rules. Option C is wrong because Network ACLs are stateless. Option D is wrong because AWS WAF is for web application layer, not network layer.
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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Question Discussion
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