- A
Configure network ACLs on the web tier subnets to allow outbound traffic and deny inbound from app tier.
Why wrong: NACLs are stateless; return traffic would be blocked.
- B
Establish VPC peering between the web and app VPCs and restrict routes.
Why wrong: Peering is transitive only via Transit Gateway, and does not enforce unidirectional traffic.
- C
Use security groups across the VPCs by referencing each other's CIDR blocks.
Why wrong: Security groups cannot reference other VPCs' groups without AWS PrivateLink.
- D
Deploy a centralized firewall appliance in a shared VPC and use Transit Gateway to route all inter-VPC traffic through it.
Enables stateful inspection and unidirectional rules.
Question 441 of 1,705
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 deploying a multi-tier application across multiple VPCs connected via AWS Transit Gateway. The web tier must be able to initiate connections to the app tier, but the app tier must not be able to initiate connections to the web tier. How can this be achieved?
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
✓
Deploy a centralized firewall appliance in a shared VPC and use Transit Gateway to route all inter-VPC traffic through it.
Option D is correct because routing all inter-VPC traffic through a centralized firewall appliance in a shared VPC via Transit Gateway allows you to enforce stateful inspection and access control policies. The firewall can be configured to permit only outbound connections from the web tier to the app tier while blocking any inbound connections initiated by the app tier, thus meeting the requirement without relying on VPC-native constructs that cannot enforce unidirectional stateful filtering across VPCs.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 network ACLs on the web tier subnets to allow outbound traffic and deny inbound from app tier.
Why it's wrong here
NACLs are stateless; return traffic would be blocked.
- ✗
Establish VPC peering between the web and app VPCs and restrict routes.
Why it's wrong here
Peering is transitive only via Transit Gateway, and does not enforce unidirectional traffic.
- ✗
Use security groups across the VPCs by referencing each other's CIDR blocks.
Why it's wrong here
Security groups cannot reference other VPCs' groups without AWS PrivateLink.
- ✓
Deploy a centralized firewall appliance in a shared VPC and use Transit Gateway to route all inter-VPC traffic through it.
Why this is correct
Enables stateful inspection and unidirectional rules.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume security groups or network ACLs can enforce unidirectional traffic across VPCs, but they are either stateless (NACLs) or stateful (security groups) and cannot prevent the app tier from initiating new connections when return traffic is allowed.
Detailed technical explanation
How to think about this question
A centralized firewall appliance (e.g., Palo Alto Networks, Fortinet, or AWS Network Firewall) performs stateful inspection, tracking TCP connection state in a state table. By configuring the firewall to allow only SYN packets from the web tier’s source IP/port to the app tier’s destination, and dropping any SYN packets from the app tier to the web tier, you achieve true unidirectional connectivity. In a real-world scenario, this architecture also simplifies compliance logging and intrusion prevention by funneling all inter-VPC traffic through a single inspection point.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy a centralized firewall appliance in a shared VPC and use Transit Gateway to route all inter-VPC traffic through it. — Option D is correct because routing all inter-VPC traffic through a centralized firewall appliance in a shared VPC via Transit Gateway allows you to enforce stateful inspection and access control policies. The firewall can be configured to permit only outbound connections from the web tier to the app tier while blocking any inbound connections initiated by the app tier, thus meeting the requirement without relying on VPC-native constructs that cannot enforce unidirectional stateful filtering across VPCs.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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