The correct answer is to create a Transit Gateway route table with a route to the Network Firewall endpoint and attach the VPCs to it. This works because the Transit Gateway acts as a central hub, and its route table must explicitly direct traffic toward the firewall’s endpoint—typically a Gateway Load Balancer endpoint or a VPC endpoint—rather than relying on subnet-level routes, which cannot forward traffic to the firewall directly. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of centralized inspection architectures, where the firewall must be a routing target in the Transit Gateway route table, not a NAT gateway or a VPC endpoint for AWS services. A common trap is confusing Network Firewall with a standard VPC security appliance; remember that the firewall endpoint is a separate resource that must be referenced in the Transit Gateway route table, not in individual subnet route tables. Memory tip: think “TGW route points to the firewall endpoint, not the subnet.”
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 is deploying an AWS Network Firewall in a centralized inspection VPC and needs to send traffic from multiple VPCs through it. The VPCs are attached to a Transit Gateway. What configuration is required to route traffic to the firewall?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a Transit Gateway route table with a route to the Network Firewall endpoint and attach the VPCs to it.
Option D is correct because the Transit Gateway route table must have a route pointing to the firewall's endpoint, and the firewall must be configured with the appropriate rules. Option A is wrong because NAT gateways do not route traffic to firewalls. Option B is wrong because VPC endpoints are for accessing AWS services. Option C is wrong because subnet routes cannot point to the firewall directly without an endpoint.
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.
✓
Create a Transit Gateway route table with a route to the Network Firewall endpoint and attach the VPCs to it.
Why this is correct
This ensures traffic is routed through the firewall.
Create a VPC Gateway Endpoint for the firewall service.
Why it's wrong here
Gateway Endpoints are used for S3 and DynamoDB, not for firewall services.
✗
Add a route in each VPC's subnet routing table pointing to the firewall's elastic network interface.
Why it's wrong here
The firewall is in a different VPC; you cannot route directly to its ENI across VPCs without Transit Gateway.
✗
Configure a NAT gateway in each VPC and route traffic through it.
Why it's wrong here
NAT gateways are for outbound internet traffic, not for traffic inspection.
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 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: Create a Transit Gateway route table with a route to the Network Firewall endpoint and attach the VPCs to it. — Option D is correct because the Transit Gateway route table must have a route pointing to the firewall's endpoint, and the firewall must be configured with the appropriate rules. Option A is wrong because NAT gateways do not route traffic to firewalls. Option B is wrong because VPC endpoints are for accessing AWS services. Option C is wrong because subnet routes cannot point to the firewall directly without an endpoint.
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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