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Question 624 of 1,705

Network Implementation →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is to use a Gateway Load Balancer (GWLB) to deploy the stateful firewall appliance in a separate subnet and configure route tables to send inter-subnet traffic to the Gateway Load Balancer endpoint. This works because GWLB acts as a transparent inline service that intercepts traffic at the subnet routing layer, allowing the firewall to inspect traffic between the web and application tiers without affecting other VPC traffic, since only the specific route entries point to the GWLB endpoint. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how to integrate third-party appliances using GWLB, a key pattern for centralized inspection without complex transitive routing. A common trap is confusing security groups or network ACLs with routing functions—remember, security groups filter but cannot route, and NACLs are stateless. Memory tip: think "GWLB = glue for stateful inspection between subnets," where the endpoint is the traffic chokepoint you control via route tables.

ANS-C01 Network Implementation Practice Question

This ANS-C01 practice question tests your understanding of network implementation. 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 is running a stateful firewall appliance in an EC2 instance in a VPC. The appliance inspects traffic between subnets. The company needs to ensure that traffic from the web tier subnet to the application tier subnet passes through the firewall, but the firewall itself must not affect other traffic. Which configuration should the company implement?

Question 1mediummultiple choice

Review the full subnetting walkthrough →

A
Place the firewall in the same subnet as the web tier and use security groups to redirect traffic.
Why wrong: Security groups do not perform routing or redirection.
B
Place the firewall in a separate subnet and use network ACLs to force traffic through it.
Why wrong: Network ACLs filter packets, they do not route traffic to a specific instance.
C
Use a Gateway Load Balancer to deploy the firewall appliance in a separate subnet, and configure route tables to send inter-subnet traffic to the Gateway Load Balancer endpoint.
GWLB transparently intercepts traffic for inspection.
D
Use a transit gateway with appliance mode and attach all subnets to it, then configure routing to send traffic through the firewall.
Why wrong: More complex and not the simplest solution.

Full breakdown with real-world context →

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

✓

Use a Gateway Load Balancer to deploy the firewall appliance in a separate subnet, and configure route tables to send inter-subnet traffic to the Gateway Load Balancer endpoint.

Option C is correct because using a Gateway Load Balancer with the firewall appliance in a separate subnet and configuring route tables with a route to the GWLBe endpoint for inter-subnet traffic is the recommended pattern. Option A is wrong because a security group cannot route traffic; it only filters. Option B is wrong because a network ACL is stateless and not suitable for stateful inspection. Option D is wrong because a transit gateway with appliance mode could work but is more complex than GWLB.

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.

✗
Place the firewall in the same subnet as the web tier and use security groups to redirect traffic.
Why it's wrong here
Security groups do not perform routing or redirection.
✗
Place the firewall in a separate subnet and use network ACLs to force traffic through it.
Why it's wrong here
Network ACLs filter packets, they do not route traffic to a specific instance.
✓
Use a Gateway Load Balancer to deploy the firewall appliance in a separate subnet, and configure route tables to send inter-subnet traffic to the Gateway Load Balancer endpoint.
Why this is correct
GWLB transparently intercepts traffic for inspection.
Related concept
CIDR notation defines the prefix length.
✗
Use a transit gateway with appliance mode and attach all subnets to it, then configure routing to send traffic through the firewall.
Why it's wrong here
More complex and not the simplest solution.

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.

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 Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Use a Gateway Load Balancer to deploy the firewall appliance in a separate subnet, and configure route tables to send inter-subnet traffic to the Gateway Load Balancer endpoint. — Option C is correct because using a Gateway Load Balancer with the firewall appliance in a separate subnet and configuring route tables with a route to the GWLBe endpoint for inter-subnet traffic is the recommended pattern. Option A is wrong because a security group cannot route traffic; it only filters. Option B is wrong because a network ACL is stateless and not suitable for stateful inspection. Option D is wrong because a transit gateway with appliance mode could work but is more complex than GWLB.

What should I do if I get this ANS-C01 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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