How AWS Transit Gateway Provides Transitive Routing for Multi-VPC Connectivity
A company has multiple VPCs in the same AWS region that need to communicate with each other. The network team wants to minimize the number of connections and simplify management. The solution must support transitive routing between all VPCs. Which AWS service should be used?
Quick Answer
The answer is AWS Transit Gateway, which is the correct choice because it provides transitive routing for multi-VPC connectivity through a hub-and-spoke architecture, allowing any attached VPC to communicate with any other via the central gateway without requiring direct peering. This eliminates the need for a full mesh of VPC peering connections—reducing N VPCs from N*(N-1)/2 connections to just N attachments—and centralizes routing management in a single routing table. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of how Transit Gateway inherently supports transitive routing, a key differentiator from VPC peering, which is non-transitive and requires explicit peering between every pair. A common trap is assuming VPC peering can scale with transitive routing, but it cannot; remember that Transit Gateway is the only native AWS service that enables transitive routing across multiple VPCs. Memory tip: think of Transit Gateway as the “hub” that lets spokes talk through it—no direct spoke-to-spoke paths needed.
⚠ Common exam trap
Candidates often confuse VPC Peering's lack of transitive routing with the ability to route through a central VPC (e.g., using a third-party appliance), but AWS explicitly prohibits transitive routing through VPC peering, making Transit Gateway the only native service that supports transitive routing between multiple VPCs.
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
✓
AWS Transit Gateway
AWS Transit Gateway (TGW) is a network transit hub that enables transitive routing between multiple VPCs and on-premises networks through a single gateway. It uses a hub-and-spoke architecture, which inherently supports transitive routing (e.g., VPC A can reach VPC C via the TGW without requiring direct peering between A and C). This minimizes the number of connections (N VPCs require only N attachments instead of N*(N-1)/2 VPC peering connections) and simplifies management with a central routing table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
VPC Peering
Why it's wrong here
Incorrect; VPC Peering does not support transitive routing.
- ✗
AWS Direct Connect Gateway
Why it's wrong here
AWS Direct Connect Gateway is designed to connect on-premises networks, via a Direct Connect connection, to multiple VPCs across different AWS regions or within the same region. It fails this scenario because it does not provide transitive routing *between* the VPCs themselves; each VPC can only communicate with the on-premises network through the gateway, not with other VPCs. This service would be the correct choice if the requirement was to centralise connectivity from an on-premises environment to multiple AWS VPCs.
- ✓
AWS Transit Gateway
Why this is correct
Correct; Transit Gateway provides transitive routing and simplifies connections.
- ✗
VPC Endpoints
Why it's wrong here
Incorrect; VPC Endpoints are for AWS service access, not VPC-to-VPC.
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1 more way this is tested on ANS-C01
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Variation 1. A company has multiple VPCs that need to communicate with each other and with an on-premises network. They want to minimize operational overhead and avoid peering mesh complexity. Which AWS service should be used?
easy- ✓ A.AWS Transit Gateway.
- B.AWS PrivateLink.
- C.AWS VPN CloudHub.
- D.VPC Peering.
Why A: AWS Transit Gateway acts as a central hub to interconnect multiple VPCs and on-premises networks using a single gateway, eliminating the need for a full mesh of VPC peering connections. It simplifies network management by providing transitive routing between all attached networks, which directly addresses the requirement to minimize operational overhead and avoid peering mesh complexity.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 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 ANS-C01 exam.