# SD-WAN Connectivity with AWS Transit Gateway Connect Attachments
Publication date: **December 28, 2024 ([Diagram history](#sdwan1-diagram-history))**
This architecture shows how to use [AWS Transit Gateway](https://docs.aws.amazon.com/vpc/latest/tgw/what-is-transit-gateway.html) Connect attachments to connect your software-defined wide area network (SD-WAN) to Transit Gateway, and simplify your route management across hybrid cloud environments. The SD-WAN headend peers with the Transit Gateway over a Generic Routing Encapsulation (GRE) tunnel, allowing this design to take advantage of the higher border gateway protocol (BGP) prefix limit of Transit Gateway. Additionally, with a single Transit Gateway Connect attachment, you can scale horizontally the bandwidth of your connection up to 20 Gbps.
## SD-WAN connectivity with AWS Transit Gateway Connect architecture
The following steps describe the AWS to on-premises traffic flow:
1. Traffic initiated from an Amazon Elastic Compute Cloud instance in the Spoke [Amazon VPC](https://docs.aws.amazon.com/vpc/latest/userguide/what-is-amazon-vpc.html) A and destined for the corporate data center is routed to the Transit Gateway elastic network interface (TGW ENI) as per the **Spoke VPC A** route table.
1. Traffic is forwarded to AWS Transit Gateway. As per the **Spoke VPC route table**, the traffic is routed to the **appliance VPC** through the Transit Gateway Connect attachment.
1. The Transit Gateway Connect attachment uses the Amazon VPC attachment as transport, and connects Transit Gateway to the third-party appliance in the **appliance VPC** using GRE tunneling and BGP.
1. The third-party virtual appliance encapsulates the traffic, which uses the SD-WAN overlay (on top of the [AWS Direct Connect](https://docs.aws.amazon.com/directconnect/latest/UserGuide/Welcome.html) link) to reach the corporate data center.
The following steps describe the on-premises to AWS traffic flow:
1. Traffic from branches outside AWS destined to the Spoke Amazon VPC B reaches the internet gateway of the **appliance VPC** through the SD-WAN overlay - on top of the internet.
1. The third-party virtual appliance in the **Connect VPC** forwards the traffic to the Transit Gateway through the Connect attachment.
1. As per the Transit Gateway Appliance Amazon VPC Route Table, the traffic is forwarded to the **Spoke VPC B** attachment.
1. The Transit Gateway ENI of the **Spoke VPC B** forwards the traffic to the destination.
For more information about AWS Transit Gateway Connect attachments and SD-WAN connectivity, see [Simplify SD-WAN connectivity with AWS Transit Gateway Connect](https://aws.amazon.com/blogs/networking-and-content-delivery/simplify-sd-wan-connectivity-with-aws-transit-gateway-connect/).
## Further reading
For additional information, see the following resources:
+ [AWS Architecture Icons](https://aws.amazon.com/architecture/icons)
+ [AWS Well-Architected](https://aws.amazon.com/architecture/well-architected)
## Diagram history
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| Change | Description | Date |
| --- |--- |--- |
| [Initial publication](#sdwan1-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
| [Initial publication](sdwan-cloudwan-connect.md#sdwan2-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
| [Initial publication](sdwan-cloudwan-tunnelless.md#sdwan3-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
| [Initial publication](sdwan-vpn-tgw.md#sdwan4-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
| [Initial publication](sdwan-vpn-cloudwan.md#sdwan5-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
| [Initial publication](sdwan-dx-tgw.md#sdwan6-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
| [Initial publication](sdwan-dx-cloudwan.md#sdwan7-diagram-history) | Reference architecture diagram first published. | December 28, 2024 |
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