- A
Configure Transit Gateway route tables to send inter-VPC traffic to the inspection VPC's attachment, and enable appliance mode on the attachment.
Appliance mode ensures that return traffic is sent back through the same firewall, enabling stateful inspection.
- B
Create VPC peering connections between all VPCs and route traffic through the central VPC.
Why wrong: VPC peering does not support transitive routing; each pair requires a direct connection.
- C
Use a Network Load Balancer in the central VPC to distribute traffic to the firewall appliances.
Why wrong: NLB does not perform packet inspection; it only load balances.
- D
Set up Direct Connect gateways and route all traffic through the on-premises network for inspection.
Why wrong: This adds unnecessary latency and complexity, and does not use Transit Gateway.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
An organization uses AWS Transit Gateway to connect multiple VPCs and on-premises networks via VPN. They want to implement traffic inspection between VPCs using a third-party firewall appliance in a central VPC. The firewall must inspect traffic for all inter-VPC flows. Which architecture meets this requirement?
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
Configure Transit Gateway route tables to send inter-VPC traffic to the inspection VPC's attachment, and enable appliance mode on the attachment.
Option A is correct because enabling appliance mode on a Transit Gateway attachment forces the Transit Gateway to preserve the source MAC address and use flow hash-based load balancing for traffic sent to the inspection VPC. This ensures that all inter-VPC traffic is routed through the third-party firewall appliance in the central VPC, allowing stateful inspection to work correctly. Without appliance mode, the Transit Gateway would perform MAC address rewriting, breaking the firewall's ability to track sessions.
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 Transit Gateway route tables to send inter-VPC traffic to the inspection VPC's attachment, and enable appliance mode on the attachment.
Why this is correct
Appliance mode ensures that return traffic is sent back through the same firewall, enabling stateful inspection.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create VPC peering connections between all VPCs and route traffic through the central VPC.
Why it's wrong here
VPC peering does not support transitive routing; each pair requires a direct connection.
- ✗
Use a Network Load Balancer in the central VPC to distribute traffic to the firewall appliances.
Why it's wrong here
NLB does not perform packet inspection; it only load balances.
- ✗
Set up Direct Connect gateways and route all traffic through the on-premises network for inspection.
Why it's wrong here
This adds unnecessary latency and complexity, and does not use Transit Gateway.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume VPC peering or a Network Load Balancer can be used for transitive routing or traffic interception, but they fail to recognize that Transit Gateway with appliance mode is the only AWS-native way to force all inter-VPC traffic through a central inspection VPC while preserving stateful firewall session integrity.
Detailed technical explanation
How to think about this question
When appliance mode is enabled on a Transit Gateway VPC attachment, the Transit Gateway stops performing MAC address translation (it no longer replaces the source MAC with its own). This allows stateful firewall appliances (e.g., Palo Alto, Fortinet) to maintain session state because they see the original source MAC and IP. The Transit Gateway also uses a consistent flow hash to forward packets from the same flow to the same firewall appliance, which is critical for stateful inspection. This behavior is defined in the AWS Transit Gateway documentation and is essential for any design that uses a third-party firewall in a central VPC for east-west traffic inspection.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
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: Configure Transit Gateway route tables to send inter-VPC traffic to the inspection VPC's attachment, and enable appliance mode on the attachment. — Option A is correct because enabling appliance mode on a Transit Gateway attachment forces the Transit Gateway to preserve the source MAC address and use flow hash-based load balancing for traffic sent to the inspection VPC. This ensures that all inter-VPC traffic is routed through the third-party firewall appliance in the central VPC, allowing stateful inspection to work correctly. Without appliance mode, the Transit Gateway would perform MAC address rewriting, breaking the firewall's ability to track sessions.
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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