What is AWS Transit Gateway?

AWS Transit Gateway (TGW) is basically the “central router” of your AWS environment. Instead of connecting every Amazon Virtual Private Cloud (VPC) to every other VPC with separate peering links, you attach each one to a single hub. TGW then handles all the routing in one place.

Think of it as AWS giving you a clean, scalable way to connect:

multiple VPCs
on-premises networks
VPN or Direct Connect links

All of this without building (and maintaining) a messy full-mesh network.

In one line:

AWS Transit Gateway is a managed hub that simplifies multi-VPC and hybrid networking by centralising connectivity and routing.

Why people actually use it:

It scales as your AWS footprint grows
You avoid hundreds of VPC-peering links
Routing becomes easier to understand and troubleshoot
You can segment traffic cleanly using route tables

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AWS Transit Gateway Architecture

AWS Transit Gateway works on a simple idea: a central hub routes traffic between all your VPCs and networks. Everything connects to this hub once, and the TGW takes care of the routing.

The Architecture in One Look

Transit Gateway (TGW): The central router
Attachments: How each VPC or on-prem network connects to the TGW
Route Tables: Tell TGW where traffic should go
Propagation: TGW learns routes from the attachments
Associations: Decide which routes apply to which attachments

Instead of wiring multiple VPC peering links, you attach each environment to TGW and manage routing in one place.

How Traffic Actually Flows

This creates a clean, predictable network design that scales far better than peering.

A VPC sends traffic to its TGW attachment.
Transit Gateway checks the associated route table.
TGW forwards the traffic to the correct target attachment.
The return path follows the same centralised route.

How Does AWS Transit Gateway Work?

The steps that need to be followed while working on AWS Transit Gateway are listed below:

Step 1: Create the Transit Gateway

You start by creating a Transit Gateway in your AWS account. At this point, it’s just an empty hub, no networks connected yet.

Step 2: Attach Your VPCs or On-Prem Networks

Next, you connect each VPC, VPN, or Direct Connect link to the TGW.

AWS calls these connections attachments.

Once attached, the VPC can send and receive traffic through the gateway.

Step 3: TGW Learns the Routes Automatically

Each attachment shares its CIDR range with the Transit Gateway.

This means TGW knows:

Which VPC owns which IP range
Where to send the traffic when a packet comes in
You don’t have to manually type every route; propagation handles that.

Step 4: You Choose Which Route Table the Attachment Uses

Transit Gateway can have multiple route tables.

You can decide:

Which VPCs should talk to each other
Which ones should stay isolated
Whether internet-bound traffic goes through a security VPC

This is where most of the network design decisions happen.

Step 5: TGW Routes the Traffic Based on These Rules

Now, when traffic arrives at the Transit Gateway:

TGW checks the correct route table
Finds the matching destination
Sends the packet out through the right attachment

This works even if the VPCs are in different AWS accounts or regions.

Step 6: Everything Flows Back Through the TGW

Return traffic follows the same centralised path.

No mesh of peering links.

No routing puzzles.

Just one clean, predictable connection point.

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AWS Transit Gateway Vs. VPC Peering

While both AWS Transit Gateway and VPC peering provide communication to Amazon Virtual Private Cloud (VPC) networks, they differ significantly in several important areas:

Aspect	AWS Transit Gateway	VPC Peering
Purpose	Connect multiple VPCs and on-premises networks	Connect two VPCs
Network Architecture	Hub-and-Spoke model	Point-to-Point model
Number of Connections	Supports up to 5,000 VPC attachments	Supports up to 125 VPC peering connections per VPC
Transitive Communication	Allows transitive routing between VPCs and on-premises	Does not allow transitive routing
Routing	Centralized route propagation and management	Each VPC must have explicit routes to reach the other VPC
Scalability	Suitable for large-scale, complex network architectures	Limited scalability for a large number of VPCs
Communication Overlapping CIDRs	Allows overlapping CIDRs between VPCs connected to the Transit Gateway	Requires non-overlapping CIDRs between VPCs

AWS Transit Gateway Pricing

The pricing for AWS Transit Gateway is based on the following factors:

1. Monthly Fee for each Transit Gateway:

The fee varies based on the size of the Transit Gateway (small, medium, or large), and it is charged regardless of the number of attachments or routes.

Small: $0.05 per hour
Medium: $0.10 per hour
Large: $0.20 per hour

2. Attachment Fee:

There is a monthly fee for each attachment to a Transit Gateway, which depends on the type of attachment:

VPC attachment: $0.05 per hour
Direct Connect attachment: $0.005 per hour
VPN attachment: $0.005 per hour

In addition to the monthly fees, there are also some other charges associated with AWS Transit Gateway, such as:

3. Data Transfer Fees:

There are data transfer charges for traffic that flows between a Transit Gateway and a VPC, Direct Connect gateway, or VPN gateway.

4. NAT gateway charges:

There are charges for NAT gateways that are used with a Transit Gateway.

5. Route fee:

There is a monthly fee for each route in a Transit Gateway, which is $0.000001 per hour.

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Benefits of AWS Transit Gateway

The following are some advantages of utilizing AWS Transit Gateway:

Provides a single point of control for traffic routing between VPCs and on-premises data centers, simplifying network administration.
Minimizes the need for several VPN connections and lowers data transmission expenses to cut costs.
Gives users more precise control over traffic filtering and routing, enhancing network security.
Allows for the implementation of hybrid architectures that combine cloud and local resources.

Use Cases of AWS Transit Gateway

Some key use cases of AWS Transit Gateway include:

1. Centralized VPC connectivity:

Transit Gateway enables seamless connectivity between multiple VPCs, allowing for centralized management and simplified network architecture.

2. Hub-and-spoke architecture:

It facilitates the creation of hub-and-spoke network topologies, where the Transit Gateway acts as the central hub, connecting VPCs and on-premises networks in a scalable and efficient manner.

3. Hybrid cloud connectivity:

Organizations can use Transit Gateway to establish secure connections between their on-premises data centers and AWS VPCs, enabling hybrid cloud architectures and extending their on-premises networks to the cloud.

4. Simplified network management:

Transit Gateway simplifies network management by reducing the need for complex peering relationships between VPCs and minimizing the number of VPN connections required.

Conclusion

To summarize, AWS Transit Gateway is a cost-effective and flexible solution that can benefit businesses across various industries and sizes. Its advantages have made it a popular choice among network architects and IT professionals who aim to optimize their infrastructure and enhance network performance. Moreover, it boasts an incredibly user-friendly interface that simplifies its usage. Unlock the power of cloud computing with our comprehensive free AWS training and take your career to new heights!