Central Traffic Inspection Across Multi-Account VPCs Using Transit Gateway
A solutions architect needs to design a network architecture for a multi-account AWS environment using AWS Transit Gateway. The company requires that all traffic between VPCs be inspected by a central security appliance. What is the MOST efficient way to achieve this?
Quick Answer
The correct answer is to attach all VPCs to a Transit Gateway and route traffic through a central inspection VPC. This design works because AWS Transit Gateway acts as a hub-and-spoke router, allowing you to direct all inter-VPC traffic through a single inspection VPC that hosts a firewall or security appliance, enforcing policy without complex peering meshes. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of centralized traffic inspection across multi-account VPCs using Transit Gateway, a common pattern for compliance and security. A frequent trap is choosing VPC peering, which lacks a central inspection point, or assuming a Network Load Balancer can inspect traffic—it cannot. Remember the mnemonic “TIGER” for Transit Gateway Inspection: Traffic In, Gateway Evaluates, Routes through inspection VPC.
⚠ Common exam trap
A common mix-up: candidates assume VPC peering is simpler or more direct, but they overlook that VPC peering lacks transitive routing, making it impossible to force all inter-VPC traffic through a single inspection point without a full mesh and complex routing.
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
✓
Attach all VPCs to a Transit Gateway and route traffic through a central inspection VPC.
AWS Transit Gateway enables a hub-and-spoke architecture where all VPCs attach to a central Transit Gateway, and a dedicated inspection VPC (with the security appliance) acts as the central inspection point. By configuring route tables in the Transit Gateway to route all inter-VPC traffic through the inspection VPC, you achieve mandatory traffic inspection without complex peering or performance bottlenecks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use AWS Direct Connect to connect all VPCs to a central on-premises firewall.
Why it's wrong here
Direct Connect is for on-premises, not inter-VPC traffic.
- ✗
Use a Network Load Balancer in each VPC to forward traffic to a firewall instance.
Why it's wrong here
NLB does not inspect traffic.
- ✓
Attach all VPCs to a Transit Gateway and route traffic through a central inspection VPC.
Why this is correct
Transit Gateway enables transitive routing with a central inspection VPC.
- ✗
Create VPC peering connections between all VPCs and route traffic through a security VPC.
Why it's wrong here
VPC peering does not support transitive routing.
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Same concept, more angles
2 more ways this is tested on SAP-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is designing a cross-account network architecture. The security team requires that all traffic between VPCs in different accounts must be inspected by a centralized firewall appliance in the security account. The network team wants to minimize complexity and avoid route table manipulation. Which solution meets these requirements?
medium- A.Use AWS PrivateLink to connect each VPC to the security VPC via interface endpoints.
- B.Set up AWS Direct Connect gateway and route all traffic through the security account.
- C.Create VPC peering connections between each VPC and the security VPC, then configure route tables to route traffic through the firewall.
- ✓ D.Use AWS Transit Gateway with a central appliance VPC, and configure route tables to send traffic to the firewall for inspection.
Why D: AWS Transit Gateway (TGW) allows you to centralize network traffic through a security appliance VPC. By attaching all VPCs to a single TGW and configuring route tables to route inter-VPC traffic to the firewall appliance in the security VPC, you meet the inspection requirement without manual route table manipulation in each spoke VPC. This design minimizes complexity by using a hub-and-spoke topology with centralized routing control.
Variation 2. A company is designing a network architecture for a multi-account AWS environment. They need to establish a central inspection VPC through which all traffic between VPCs in different accounts must pass. Which AWS service should be used to route traffic between VPCs through the inspection VPC?
easy- A.AWS Direct Connect gateway
- B.VPC peering with full mesh connectivity
- C.Elastic Load Balancer
- ✓ D.AWS Transit Gateway
Why D: AWS Transit Gateway (D) is the correct service because it acts as a central hub that can route traffic between multiple VPCs across different accounts, and it supports route tables that can force all inter-VPC traffic through a dedicated inspection VPC (e.g., using a blackhole route or a network appliance). This enables transitive routing without requiring full mesh peering, and it integrates with AWS Resource Access Manager (RAM) for cross-account sharing.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAP-C02 exam.