- A
Update Web-SG to allow SSH from a specific management CIDR. Leave App-SG and DB-SG as is because they are not directly accessible from the internet.
Why wrong: App-SG still allows SSH from 0.0.0.0/0, which is a security risk, and DB-SG allows access from anywhere.
- B
Remove inbound SSH rules from all security groups and rely on AWS Systems Manager Session Manager for administrative access.
Why wrong: While Session Manager is a good practice, the question asks for a course of action to remediate the issues; this option does not address the application tier and database tier inbound rules.
- C
Update Web-SG to allow SSH from a specific management CIDR. Update App-SG to allow inbound on port 8080 from Web-SG only, and remove inbound SSH from App-SG (or restrict to management CIDR). Update DB-SG to allow inbound on port 3306 from App-SG only.
This properly restricts traffic to only necessary sources and removes open SSH access.
- D
Use network ACLs on the subnets to restrict traffic between tiers instead of security groups.
Why wrong: Security groups are stateful and easier to manage for this scenario; network ACLs are stateless and would require more complex rules.
ANS-C01 Network Security, Compliance and Governance Practice Question
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 company runs a multi-tier application on AWS. The web tier consists of EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The application tier runs on EC2 instances in a separate Auto Scaling group, and the database tier uses an Amazon RDS MySQL instance. All resources are in the same VPC. The security team has identified that the application tier instances are receiving traffic from unknown IP addresses on port 22 (SSH). The team wants to ensure that only the web tier instances can communicate with the application tier on the application port (8080), and only from a specific security group. Additionally, the database tier should only accept traffic from the application tier on port 3306. Currently, the security groups are configured as follows: Web-SG allows inbound from 0.0.0.0/0 on ports 80 and 443; App-SG allows inbound from 0.0.0.0/0 on port 8080 and from 0.0.0.0/0 on port 22; DB-SG allows inbound from 0.0.0.0/0 on port 3306. The team has also noticed that the web tier instances can be accessed via SSH from the internet. Which course of action should the team take to remediate the security issues?
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
Update Web-SG to allow SSH from a specific management CIDR. Update App-SG to allow inbound on port 8080 from Web-SG only, and remove inbound SSH from App-SG (or restrict to management CIDR). Update DB-SG to allow inbound on port 3306 from App-SG only.
The correct action is to update the security groups to restrict inbound traffic: Web-SG should allow SSH only from a trusted management IP, not from 0.0.0.0/0. App-SG should allow inbound on port 8080 only from Web-SG, and not allow SSH from 0.0.0.0/0. DB-SG should allow inbound on port 3306 only from App-SG. Option A achieves this. Option B only addresses the web tier SSH issue. Option C removes SSH entirely, which might be needed for management. Option D uses network ACLs but NACLs are stateless and would require complex rules; security groups are more appropriate for this use case.
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.
- ✗
Update Web-SG to allow SSH from a specific management CIDR. Leave App-SG and DB-SG as is because they are not directly accessible from the internet.
Why it's wrong here
App-SG still allows SSH from 0.0.0.0/0, which is a security risk, and DB-SG allows access from anywhere.
- ✗
Remove inbound SSH rules from all security groups and rely on AWS Systems Manager Session Manager for administrative access.
Why it's wrong here
While Session Manager is a good practice, the question asks for a course of action to remediate the issues; this option does not address the application tier and database tier inbound rules.
- ✓
Update Web-SG to allow SSH from a specific management CIDR. Update App-SG to allow inbound on port 8080 from Web-SG only, and remove inbound SSH from App-SG (or restrict to management CIDR). Update DB-SG to allow inbound on port 3306 from App-SG only.
- ✗
Use network ACLs on the subnets to restrict traffic between tiers instead of security groups.
Why it's wrong here
Security groups are stateful and easier to manage for this scenario; network ACLs are stateless and would require more complex rules.
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 easier to manage for this scenario; network ACLs are stateless and would require more complex rules.
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: Update Web-SG to allow SSH from a specific management CIDR. Update App-SG to allow inbound on port 8080 from Web-SG only, and remove inbound SSH from App-SG (or restrict to management CIDR). Update DB-SG to allow inbound on port 3306 from App-SG only. — The correct action is to update the security groups to restrict inbound traffic: Web-SG should allow SSH only from a trusted management IP, not from 0.0.0.0/0. App-SG should allow inbound on port 8080 only from Web-SG, and not allow SSH from 0.0.0.0/0. DB-SG should allow inbound on port 3306 only from App-SG. Option A achieves this. Option B only addresses the web tier SSH issue. Option C removes SSH entirely, which might be needed for management. Option D uses network ACLs but NACLs are stateless and would require complex rules; security groups are more appropriate for this use case.
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
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