Data processing costs of TGW-Cloud WAN mixed setup(Federating Transit Gateways with Cloud WAN)

Question

in the article "https://aws.amazon.com/blogs/networking-and-content-delivery/aws-cloud-wan-and-aws-transit-gateway-migration-and-interoperability-patterns/"
Cloud WAN is presented as initially being inserted to provide connectivity between TGW's and job is done.

**Federating Transit Gateways with Cloud WAN – In this model you replace statically created Transit Gateway peering connections with Cloud WAN. This results in simple connectivity and global dynamic routing. If you like, you can stop your migration here and use Cloud WAN as a dynamic routing hub for your Transit Gateways.**

That works wonders and would be ideal. But I got below feedback as well from AWS. 
**"So with TGW - CWAN - TGW... there's 2 traffic processing charges (as one peering is treated as one, but the other TGW is another resource there). Same as TGW - TGW - TGW"**
The explanation about costs I could not reference anywhere on a public facing article by AWS.

As amazon states publicly (https://aws.amazon.com/transit-gateway/pricing/)
Data processing charges apply for each gigabyte sent from a VPC, Direct Connect or VPN to the AWS Transit Gateway
Data processing charges do not apply for data sent from a peering attachment to a Transit Gateway. Data transferred over a peering attachment incurs the standard inter-Region data transfer charges.

But they also stated in direct communication that the "Data processing charges do not apply for data sent from a peering attachment to a Transit Gateway" applies for 2 hops only. So in a TGW-CloudWan-TGW scenario, you have 
(TGW-**no fee**-CloudWan)-**paid data processing** - TGW

So wanted a confirmation if anyone has it in production : do you get charged twice for data processing if you use the "Federating Transit Gateways with Cloud WAN" model?

kind regards.

Tom_Adamski · Answer

There are two distinct data related charges when it comes to TGW or Cloud WAN:

* **Data Processin**g - Applied on AWS managed networking services that process the data such as NAT Gateway, Transit Gateway, Cloud WAN, PrivateLink Endpoints etc. The data processing costs and directions it applies to is documented under each service's pricing page.
* **Data Transfer** - Charges applied to data transferred between an AWS resource and different network destinations i.e. cross-AZ, to Internet, in-Region, cross-Region. The pricing is dependent on the AWS Region and is documented here: https://aws.amazon.com/ec2/pricing/on-demand/
  * Regional data transfer charges are typically applied to `out` and `in` directions, meaning that both the sender and receiver of data can be charged.

Here is how these apply to **Cloud WAN and Transit Gateway**

* **Data Processing** - there is no data processing applied to traffic between peered TGW and Cloud WAN. Data processing is applied to traffic arriving to TGW from a TGW attachment (i.e. VPC, VPN) or arriving to Cloud WAN on a Cloud WAN attachment (i.e. VPC, VPN etc)
* **Data Transfer** - Regional data transfer charges are applied for traffic between TGW and Cloud WAN. Cloud WAN applies data transfer charges for both `in` and `out` direction (charges applied when Cloud WAN receives data and sends data from/to TGW) while TGW applies data transfer only in the `out` direction (charges applied when TGW sends data to Cloud WAN).

The diagram below depicts all of the data related charges (processing in orange box and transfer in blue box) for traffic flowing across TGW and Cloud WAN peering. It also shows the data transfer costs for cross Region as well as DX connectivity. Note, the diagram doesn't include any hourly charges and that the prices are based on pricing pages at the time of this post.

![Enter image description here](/media/postImages/original/IMgcz-wM35TCmlFQdYStqwSg)

If the VPC on the left sends 1GB of data to on-premises (on far right) here are the charges applied on each hop:

1. $0.02 TGW applied [data processing](https://aws.amazon.com/transit-gateway/pricing/) charge for incoming traffic
2. $0.01 TGW [regional data transfer](https://aws.amazon.com/ec2/pricing/on-demand/#:~:text=In%20case%20of%20AWS%20Transit%20Gateway%20peering%2C%20data%20transferred%20%22out%22%20from%20each%20Transit%20Gateway%20using%20private%20IP%20addresses%2C%20is%20charged%20at%20%240.01/GB%20in%20the%20same%20AWS%20Region.) applied to the `out` direction
3. $0.01 Cloud WAN [regional data transfer](https://aws.amazon.com/ec2/pricing/on-demand/#:~:text=In%20case%20of%20AWS%20Transit%20Gateway%20and%20AWS%20Cloud%20WAN%20peering%2C%20data%20transferred%20%22out%22%20from%20Transit%20Gateway%20using%20private%20IP%20addresses%2C%20is%20charged%20at%20%240.01/GB%20and%20data%20transferred%20%22in%22%20to%20and%20%22out%22%20from%20Cloud%20WAN%20using%20private%20IP%20addresses%20is%20charged%20at%20%240.01/GB%20in%20the%20same%20AWS%20Region.) applied to the `in` direction
4. $0.02 Cross Region data transfer between us-east-1 and us-west-2 in the `out` direction
5. $0.01 Cloud WAN regional data transfer applied to the `out` direction
6. $xx Direct Connect [data transfer ](https://aws.amazon.com/directconnect/pricing/)applied to the `out` direction. Value depends on the combination of Regions and DX location

Please refer to [AWS EC2 Data Transfer Pricing](https://aws.amazon.com/ec2/pricing/on-demand/#Data_Transfer_within_the_same_AWS_Region) for more details.

Data processing costs of TGW-Cloud WAN mixed setup(Federating Transit Gateways with Cloud WAN)

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