Quick Answer
The answer is AWS Network Firewall, as it is the only AWS service capable of performing stateful, deep packet inspection for traffic between instances within the same VPC, including traffic that stays entirely within a single subnet. This capability is critical because AWS Network Firewall is deployed as a managed service in a dedicated subnet and can be configured with a firewall endpoint in each Availability Zone, allowing it to intercept and inspect all east-west traffic, even intra-subnet flows, by routing that traffic through the firewall using VPC route tables. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of the differences between network inspection services—a common trap is confusing AWS Network Firewall with AWS WAF, which only inspects HTTP/HTTPS traffic at layer 7, or with Security Groups, which are stateless and cannot perform content inspection. A helpful memory tip: think of AWS Network Firewall as the “full packet inspector” for all VPC traffic, while WAF is just for web apps, and Security Groups are simple stateful filters.
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 security engineer is designing a network firewall solution for a VPC with multiple subnets. The solution must inspect traffic between instances in the same VPC, including traffic within the same subnet. Which AWS service should be used?
Security Groups
Why wrong: Act as a virtual firewall at the instance level, but not for deep packet inspection.
VPC Flow Logs
Why wrong: Capture IP traffic information but do not inspect or block traffic.
AWS Network Firewall
Provides stateful and stateless inspection for all VPC traffic.
AWS WAF
Why wrong: Designed to protect web applications from common web exploits.
Answer choices
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 A is correct because AWS Network Firewall can inspect traffic between subnets and within a subnet when deployed in a VPC. Option B is wrong because AWS WAF is for web application layer 7 inspection, not for general network traffic. Option C is wrong because Security Groups are stateless and cannot perform deep packet inspection. Option D is wrong because VPC Flow Logs only capture metadata, not inspect packets.
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
For each option: why learners choose it and why it is or isn't the right answer here.
Security Groups
Why it's wrong here
Act as a virtual firewall at the instance level, but not for deep packet inspection.
VPC Flow Logs
Why it's wrong here
Capture IP traffic information but do not inspect or block traffic.
AWS Network Firewall
Why this is correct
Provides stateful and stateless inspection for all VPC traffic.
Related concept
CIDR notation defines the prefix length.
AWS WAF
Why it's wrong here
Designed to protect web applications from common web exploits.
Common exam traps
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
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.
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
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
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
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
The correct answer is: AWS Network Firewall — Option A is correct because AWS Network Firewall can inspect traffic between subnets and within a subnet when deployed in a VPC. Option B is wrong because AWS WAF is for web application layer 7 inspection, not for general network traffic. Option C is wrong because Security Groups are stateless and cannot perform deep packet inspection. Option D is wrong because VPC Flow Logs only capture metadata, not inspect packets.
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.
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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