The answer is to use security groups that reference other security groups as sources. This is correct because security groups act as a virtual firewall at the instance level, and by referencing the web tier’s security group ID in the application tier’s inbound rule, you allow traffic only from instances in that specific group—regardless of IP changes. Similarly, the database tier can reference the application tier’s security group on port 3306, creating a tightly scoped, dynamic trust chain. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this tests your understanding of stateful, instance-level filtering versus stateless network ACLs, which are also needed at the subnet level for defense in depth. A common trap is confusing security group referencing with IP-based rules or assuming IAM or WAF handles tier-to-tier traffic. Memory tip: think “chain of trust” – each tier only trusts the security group ID of the tier feeding it, not an IP range.
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 engineer is designing a network security solution for a multi-tier application. The web tier must be accessible from the internet on ports 80 and 443. The application tier must only accept traffic from the web tier. The database tier must only accept traffic from the application tier on port 3306. Which THREE network access control mechanisms should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Security groups that allow traffic from specific security groups for the database tier.
Option A is correct because security groups can be used to allow traffic between tiers based on security group IDs. Option C is correct because network ACLs provide stateless filtering at the subnet level. Option E is correct because security groups for the database tier can reference the application tier security group. Option B is wrong because IAM is for identity management, not network filtering. Option D is wrong because AWS WAF is for web application firewall at the application layer, not for network-level access between tiers.
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 groups that allow traffic from specific security groups for the database tier.
Why this is correct
Database security groups should allow inbound traffic from the application security group.
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: Security groups that allow traffic from specific security groups for the database tier. — Option A is correct because security groups can be used to allow traffic between tiers based on security group IDs. Option C is correct because network ACLs provide stateless filtering at the subnet level. Option E is correct because security groups for the database tier can reference the application tier security group. Option B is wrong because IAM is for identity management, not network filtering. Option D is wrong because AWS WAF is for web application firewall at the application layer, not for network-level access between tiers.
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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