This SCS-C02 practice question tests your understanding of infrastructure security. 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 uses an AWS Transit Gateway to connect multiple VPCs and on-premises networks. A security engineer needs to ensure that traffic between VPCs is inspected by a third-party firewall appliance. Which architecture should be used?
Configure security groups on the transit gateway to inspect traffic.
Why wrong: Security groups cannot be attached to transit gateways; they are used for EC2 instances and other resources.
B
Create VPC endpoints for each VPC to route traffic through the firewall.
Why wrong: VPC endpoints are for accessing AWS services, not for traffic inspection.
C
Attach the firewall appliance to a dedicated inspection VPC and route traffic from other VPCs through the inspection VPC using transit gateway route tables.
This is the common architecture for centralized traffic inspection using a transit gateway.
D
Use network ACLs on the transit gateway to filter traffic.
Why wrong: Network ACLs are applied at the subnet level, not on transit gateways.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Attach the firewall appliance to a dedicated inspection VPC and route traffic from other VPCs through the inspection VPC using transit gateway route tables.
The correct answer is D because by attaching the firewall appliance in a dedicated inspection VPC and using route tables to direct traffic through it, you can inspect inter-VPC traffic. Option A is wrong because security groups are instance-level firewalls and cannot inspect all traffic in a transit gateway. Option B is wrong because network ACLs are stateless and applied at subnet level, not at transit gateway level. Option C is wrong because VPC endpoints are for accessing AWS services privately, not for traffic inspection.
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.
✗
Configure security groups on the transit gateway to inspect traffic.
Why it's wrong here
Security groups cannot be attached to transit gateways; they are used for EC2 instances and other resources.
✗
Create VPC endpoints for each VPC to route traffic through the firewall.
Why it's wrong here
VPC endpoints are for accessing AWS services, not for traffic inspection.
✓
Attach the firewall appliance to a dedicated inspection VPC and route traffic from other VPCs through the inspection VPC using transit gateway route tables.
Why this is correct
This is the common architecture for centralized traffic inspection using a transit gateway.
Use network ACLs on the transit gateway to filter traffic.
Why it's wrong here
Network ACLs are applied at the subnet level, not on transit gateways.
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
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Attach the firewall appliance to a dedicated inspection VPC and route traffic from other VPCs through the inspection VPC using transit gateway route tables. — The correct answer is D because by attaching the firewall appliance in a dedicated inspection VPC and using route tables to direct traffic through it, you can inspect inter-VPC traffic. Option A is wrong because security groups are instance-level firewalls and cannot inspect all traffic in a transit gateway. Option B is wrong because network ACLs are stateless and applied at subnet level, not at transit gateway level. Option C is wrong because VPC endpoints are for accessing AWS services privately, not for traffic inspection.
What should I do if I get this SCS-C02 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 SCS-C02 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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