The answer is to use security groups to control traffic at the instance level, place databases in private subnets, and apply network ACLs as a stateless firewall layer. These three best practices form the foundation of multi-tier web application network security on AWS because they enforce defense in depth: security groups act as a stateful virtual firewall at the instance level, private subnets isolate sensitive database tiers from direct internet exposure, and NACLs provide a stateless, subnet-wide rule set that can explicitly block traffic before it reaches the security group layer. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of the critical distinction between stateful and stateless controls—a common trap is confusing security groups (stateful) with NACLs (stateless), or incorrectly attaching an internet gateway to a private subnet. Remember the mnemonic: "SGs are stateful, NACLs are not; private subnets keep databases in the vault."
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 company is designing a network security architecture for a multi-tier web application. Which THREE best practices should they implement? (Choose three.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use network ACLs as a stateless firewall for subnet-level traffic
Options A, C, and E are correct. A: Use security groups as a virtual firewall. C: Use private subnets for databases. E: Use NACLs as a stateless firewall layer. Option B is wrong because security groups are stateful, not stateless. Option D is wrong because the internet gateway should be attached to public subnets, not private.
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.
✗
Attach an internet gateway to the private subnet for outbound traffic
Why it's wrong here
Internet gateway should be attached to public subnets; use NAT for private subnets.
✗
Use security groups as a stateless firewall
Why it's wrong here
Security groups are stateful, not stateless.
✓
Use network ACLs as a stateless firewall for subnet-level traffic
Why this is correct
NACLs are stateless and provide subnet-level filtering.
Clue confirmation
The clue word "best" in the question point toward this answer.
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.
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: Use network ACLs as a stateless firewall for subnet-level traffic — Options A, C, and E are correct. A: Use security groups as a virtual firewall. C: Use private subnets for databases. E: Use NACLs as a stateless firewall layer. Option B is wrong because security groups are stateful, not stateless. Option D is wrong because the internet gateway should be attached to public subnets, not private.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is designing a network security architecture for a multi-tier application. The web tier must be accessible from the internet, but the application and database tiers must not. Which TWO design choices meet these requirements? (Choose two.)
medium
A.Use a VPC Gateway Endpoint for the web tier to access the internet.
B.Use a NAT gateway in a public subnet to provide internet access to the app and database tiers for updates.
✓ C.Use a security group on the web tier to allow HTTP/HTTPS from 0.0.0.0/0, and security groups on the app and database tiers that only allow traffic from the web tier security group.
D.Place all tiers in a public subnet with a security group that restricts access to the app and database tiers.
✓ E.Place the web tier in a public subnet with an internet gateway in the route table, and the app and database tiers in private subnets.
Why C: Options B and C are correct because public subnets for the web tier with a security group that allows HTTP/HTTPS from the internet, and private subnets for app and database tiers with no internet gateway route, ensure the required access. Option A is wrong because a single public subnet for all tiers exposes app and database. Option D is wrong because a NAT gateway is for outbound traffic, not inbound. Option E is wrong because a VPC endpoint does not provide internet access to the web tier.
Variation 2. A company is designing a network security architecture for a multi-tier application. The web tier must be accessible from the internet, while the application and database tiers must be isolated. The security team wants to minimize the attack surface. Which design should they choose?
medium
✓ A.Place the web tier in public subnets with an internet gateway, and the app and DB tiers in private subnets. Use security groups to allow traffic only from the web tier to the app tier and from the app tier to the DB tier.
B.Place all tiers in private subnets and use a NAT gateway for internet access.
C.Place all tiers in the same subnet and use a single security group for all instances.
D.Place all tiers in public subnets and use network ACLs to restrict inbound traffic to the app and DB tiers.
Why A: Using public subnets for web tier and private subnets for app and DB tiers, with security groups to control traffic, is best practice. Option A is correct. Option B is wrong because NACLs are stateless and less flexible than security groups for traffic filtering. Option C is wrong because putting all tiers in public subnets increases attack surface. Option D is wrong because using one security group for all tiers violates least privilege.
Variation 3. A company is designing a network security architecture for a multi-tier application. Which TWO of the following are best practices for implementing defense in depth?
medium
A.Use network ACLs as stateful firewalls at the subnet level
✓ B.Use security groups to control traffic between instances
C.Attach internet gateways to all subnets for high availability
✓ D.Place web servers in public subnets and application servers in private subnets
E.Use the same security group for all tiers to simplify management
Why B: Option A is correct because placing web servers in public subnets and app servers in private subnets adds a layer of separation. Option C is correct because using security groups as instance-level firewalls provides granular control. Option B is wrong because network ACLs are stateless and not stateful. Option D is wrong because public subnets should not have direct internet access for tiers that don't need it. Option E is wrong because using the same security group for all tiers reduces security.
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