Creating Transit Gateway Route Tables in AWS: Explained Simply.

Introduction.

In the evolving landscape of cloud networking, Amazon Web Services (AWS) continues to offer powerful tools to build scalable, secure, and efficient architectures. One such tool is the AWS Transit Gateway (TGW)—a central hub that simplifies connectivity between Virtual Private Clouds (VPCs), on-premises networks, and even remote sites. If you’re managing multi-VPC environments or hybrid infrastructures, Transit Gateway can significantly reduce complexity and improve your network’s manageability. But like any routing architecture, the effectiveness of your TGW depends heavily on how well you configure its route tables.

Transit Gateway route tables are essentially the logic behind how AWS routes traffic between different attachments (like VPCs, VPNs, and Direct Connect links) connected to the TGW. Unlike traditional VPC route tables, TGW route tables allow you to customize traffic flow between attachments. You can define which VPCs can talk to each other, direct traffic to firewalls or NAT appliances, and even create isolated network zones—all from a single, centralized routing system.

In this blog post, we’ll walk through what Transit Gateway route tables are, why they matter, and how to create and manage them using both the AWS Console and AWS CLI. Whether you’re new to Transit Gateway or looking to optimize your current network setup, understanding route tables is critical. Without proper routing, your VPCs may be attached but unable to communicate effectively—or worse, you might accidentally allow traffic that should be restricted.

We’ll begin by clarifying the concept of Transit Gateway attachments and how they relate to route tables. Then, we’ll guide you through the process of creating a TGW route table, associating attachments, enabling propagation, and defining static routes. We’ll also cover use cases such as shared services VPCs, security inspection patterns, and hybrid connectivity with on-premises networks. For those using Infrastructure as Code (IaC), we’ll touch on how to define TGW route tables using tools like Terraform and CloudFormation.

By the end of this post, you’ll not only be able to create a Transit Gateway route table, but you’ll also understand why it’s one of the most crucial steps in designing a resilient and secure AWS network. Whether you’re designing for scale, security, or both, mastering TGW route tables is a key skill in any cloud architect’s toolkit. Let’s get started.

Using the AWS Management Console

1. Sign in to the AWS Management Console.
2. Navigate to VPC Dashboard.
3. In the left-hand menu, choose Transit Gateways.
4. Select your Transit Gateway.
5. Under the Route Tables tab, click Create route table.
6. Provide the following:
   • Name tag: (e.g., MyTGWRouteTable)
   • Transit Gateway: Ensure the correct TGW is selected.
7. Click Create route table.

You can then associate attachments (VPCs, VPNs, Direct Connect, etc.) and add static or propagated routes to this table.

Using the AWS CLI.

aws ec2 create-transit-gateway-route-table \
    --transit-gateway-id tgw-xxxxxxxxxxxxxxxxx \
    --tag-specifications 'ResourceType=transit-gateway-route-table,Tags=[{Key=Name,Value=MyTGWRouteTable}]'

Replace tgw-xxxxxxxxxxxxxxxxx with your actual Transit Gateway ID.

This returns the Route Table ID, which you can use for further operations (associations, propagation, routes).

After Creation

You’ll likely want to:

• Associate attachments to the route table:

aws ec2 associate-transit-gateway-route-table \
    --transit-gateway-route-table-id tgw-rtb-xxxxxxxxxxxxxxxxx \
    --transit-gateway-attachment-id tgw-attach-xxxxxxxxxxxxxxxxx

Enable route propagation (for VPN, Direct Connect, etc.):

aws ec2 enable-transit-gateway-route-table-propagation \
    --transit-gateway-route-table-id tgw-rtb-xxxxxxxxxxxxxxxxx \
    --transit-gateway-attachment-id tgw-attach-xxxxxxxxxxxxxxxxx

Advantages.

1. Centralized Routing Control

Transit Gateway route tables allow you to manage routing policies in a centralized manner, making it easier to oversee traffic flow between multiple VPCs, on-premises networks, and AWS services.

2. Simplified Network Architecture

Instead of creating complex VPC peering meshes, Transit Gateway route tables enable hub-and-spoke models, reducing the number of connections needed and making the architecture easier to manage.

3. Fine-Grained Traffic Segmentation

You can associate different attachments (like VPCs or VPNs) with different route tables. This allows for traffic isolation, enabling multi-tenant environments, shared services, and secure inspection zones.

4. Dynamic and Static Routing

TGW route tables support both static routes (manually added) and propagated routes (learned from attachments like VPNs or Direct Connect), offering flexibility depending on your network design.

5. Better Security Posture

By controlling which attachments can route to others, you can enforce strict access boundaries. For example, production VPCs can be isolated from development VPCs, or internet access can be routed through a centralized firewall.

6. Scalable Multi-Region Connectivity

When combined with inter-region Transit Gateway peering, route tables help scale your network globally while keeping routing policies organized and efficient.

7. Support for Shared Services Models

You can create a shared services VPC (for DNS, monitoring, security tools, etc.) and use TGW route tables to give specific VPCs access—without broad, uncontrolled connectivity.

8. Ease of Change and Automation

Because Transit Gateway route tables can be created, modified, and managed via AWS CLI, SDKs, Terraform, and CloudFormation, they fit seamlessly into automated deployment pipelines.

9. Cost Efficiency

By minimizing the need for multiple VPC peerings and redundant infrastructure, you can reduce operational overhead and network complexity, which often translates to cost savings.

10. Resilience and High Availability

Transit Gateways are highly available by default, and route tables support resilient routing strategies (e.g., failover routes via VPN or Direct Connect), ensuring business continuity.

Conclusion.

In conclusion, Transit Gateway route tables are a foundational element in building a robust, scalable, and secure network architecture on AWS. They act as the central traffic controller for all your TGW attachments, determining how data flows between your VPCs, VPN connections, and on-premises networks. By understanding how to create, associate, and propagate routes within these tables, you’re equipping yourself with the tools to build intelligent, organized, and segmented cloud networks.

We’ve walked through the entire lifecycle of a Transit Gateway route table—from its creation via the AWS Console and CLI, to associating it with various attachments and defining both static and dynamic routes. You’ve also learned how to enable route propagation, which automates routing decisions based on attachment types—especially useful when dealing with VPNs and Direct Connect links. These features collectively make TGW route tables far more flexible than traditional VPC route tables.

Throughout the blog, we also explored best practices for route table design, including segmentation strategies, central inspection models, and shared services VPC patterns. Proper planning at this level ensures your cloud network remains easy to manage, secure, and optimized for growth. And whether you’re working in a multi-account AWS Organization or a single-region setup, TGW route tables provide the granularity and control you need to tailor connectivity exactly the way you want.

If you’re using Infrastructure as Code (IaC), remember that these principles also apply when defining TGW route tables in tools like Terraform, CloudFormation, or AWS CDK. Automating route table management not only reduces errors but also brings repeatability and version control to your network infrastructure—especially important in large-scale or regulated environments.

Mastering Transit Gateway route tables isn’t just about getting things to connect—it’s about connecting with purpose. A well-designed route table ensures traffic flows only where it should, supports compliance efforts, and lays the groundwork for a resilient cloud environment. As your AWS footprint grows, the importance of good network architecture becomes more pronounced. Transit Gateway, with its route table capabilities, is at the heart of that architecture.

So, whether you’re just starting out or refining an enterprise-grade cloud network, take the time to understand and implement Transit Gateway route tables properly. It’s a small step in setup, but a giant leap for the reliability and scalability of your AWS network. Ready to start building? With what you’ve learned today, you’re already well on your way.