- A
Add a route in the route table associated with subnet A that sends all traffic to the firewall endpoint.
Why wrong: This would send all traffic, not just to subnet B, and return traffic from subnet B would not go through the firewall.
- B
Add a route in the route table for subnet A with destination subnet B CIDR and target the firewall endpoint. Add a similar route in subnet B's route table with destination subnet A CIDR and target the firewall endpoint.
This ensures both directions go through the firewall.
- C
Add a route in the route table associated with subnet B that sends all traffic to the firewall endpoint.
Why wrong: Only inbound traffic to subnet B would go through firewall, but outbound from A would not.
- D
Associate both subnets with the same route table and add a route to the firewall endpoint for all traffic.
Why wrong: Subnets in different tiers typically have different route tables, and this would send all traffic, not just cross-tier.
SCS-C02 Infrastructure Security Practice Question
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 Network Firewall to inspect traffic between subnets in a VPC. The security team wants to ensure that all traffic from the web tier to the database tier passes through the firewall. The web servers are in subnet A, and the database servers are in subnet B. What routing configuration is required?
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
Add a route in the route table for subnet A with destination subnet B CIDR and target the firewall endpoint. Add a similar route in subnet B's route table with destination subnet A CIDR and target the firewall endpoint.
The correct answer is B. To force traffic between subnets through the AWS Network Firewall, you need symmetric routes: add a route in subnet A's route table for destination subnet B CIDR with target the firewall endpoint, and similarly add a route in subnet B's route table for destination subnet A CIDR with target the firewall endpoint. This ensures both forward and return traffic pass through the firewall. Option A is wrong because it sends all traffic from subnet A to the firewall, which is overly broad and may break other traffic; more importantly, it does not ensure return traffic from subnet B goes through the firewall. Option C is wrong because it only handles return traffic from subnet B but not the forward traffic from subnet A. Option D is wrong because both subnets cannot be in the same route table if they need different routes; also, sending all traffic from both subnets to the firewall is not the correct setup for inter-subnet 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.
- ✗
Add a route in the route table associated with subnet A that sends all traffic to the firewall endpoint.
Why it's wrong here
This would send all traffic, not just to subnet B, and return traffic from subnet B would not go through the firewall.
- ✓
Add a route in the route table for subnet A with destination subnet B CIDR and target the firewall endpoint. Add a similar route in subnet B's route table with destination subnet A CIDR and target the firewall endpoint.
- ✗
Add a route in the route table associated with subnet B that sends all traffic to the firewall endpoint.
Why it's wrong here
Only inbound traffic to subnet B would go through firewall, but outbound from A would not.
- ✗
Associate both subnets with the same route table and add a route to the firewall endpoint for all traffic.
Why it's wrong here
Subnets in different tiers typically have different route tables, and this would send all traffic, not just cross-tier.
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 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.
Visual reference
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.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
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: Add a route in the route table for subnet A with destination subnet B CIDR and target the firewall endpoint. Add a similar route in subnet B's route table with destination subnet A CIDR and target the firewall endpoint. — The correct answer is B. To force traffic between subnets through the AWS Network Firewall, you need symmetric routes: add a route in subnet A's route table for destination subnet B CIDR with target the firewall endpoint, and similarly add a route in subnet B's route table for destination subnet A CIDR with target the firewall endpoint. This ensures both forward and return traffic pass through the firewall. Option A is wrong because it sends all traffic from subnet A to the firewall, which is overly broad and may break other traffic; more importantly, it does not ensure return traffic from subnet B goes through the firewall. Option C is wrong because it only handles return traffic from subnet B but not the forward traffic from subnet A. Option D is wrong because both subnets cannot be in the same route table if they need different routes; also, sending all traffic from both subnets to the firewall is not the correct setup for inter-subnet 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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Last reviewed: Jun 20, 2026
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