Example: Peered transit gateways
You can create a transit gateway peering connection between transit gateways. You can then route traffic between the attachments for each of the transit gateways. In this scenario, VPC and VPN attachments are associated with the transit gateway default route tables, and they propagate to the transit gateway default route tables. Each transit gateway route table has a static route that points to the transit gateway peering attachment.
Overview
The following diagram shows the key components of the configuration for this scenario. Transit gateway 1 has two VPC attachments, and transit gateway 2 has one Site-to-Site VPN attachment. Packets from the subnets in VPC A and VPC B that have the internet as a destination first route through transit gateway 1, then transit gateway 2, and then route to the VPN connection.
Resources
Create the following resources for this scenario:
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Two VPCs. For information about creating a VPC, see Create a VPC in the Amazon VPC User Guide.
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Two transit gateways. They can be in the same Region or in different Regions. For more information, see Create a transit gateway.
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Two VPC attachments on the first transit gateway. For more information, see Create a transit gateway attachment to a VPC.
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A Site-to-Site VPN attachment on the second transit gateway. For more information, see Create a transit gateway attachment to a VPN. Ensure that you review the requirements for your customer gateway device in the AWS Site-to-Site VPN User Guide.
-
A transit gateway peering attachment between the two transit gateways. For more information, see Transit gateway peering attachments.
When you create the VPC attachments, the CIDRs for each VPC propagate to the route table for transit gateway 1. When the VPN connection is up, the following actions occur:
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The BGP session is established
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The Site-to-Site VPN CIDR propagates to the route table for transit gateway 2
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The VPC CIDRs are added to the customer gateway BGP table
Routing
Each VPC has a route table and each transit gateway has a route table.
VPC A and VPC B route tables
Each VPC has a route table with 2 entries. The first entry is the default entry for local IPv4 routing in the VPC. This default entry enables the resources in this VPC to communicate with each other. The second entry routes all other IPv4 subnet traffic to the transit gateway. The following table shows the VPC A routes.
| Destination | Target |
|---|---|
|
10.0.0.0/16 |
local |
|
0.0.0.0/0 |
tgw-1-id |
Transit gateway route tables
The following is an example of the default route table for transit gateway 1, with route propagation enabled.
| Destination | Target | Route type |
|---|---|---|
|
10.0.0.0/16 |
|
propagated |
|
10.2.0.0/16 |
|
propagated |
|
0.0.0.0/0 |
Attachment ID for peering connection |
static |
The following is an example of the default route table for transit gateway 2, with route propagation enabled.
| Destination | Target | Route type |
|---|---|---|
|
172.31.0.0/24 |
Attachment ID for VPN connection |
propagated |
|
10.0.0.0/16 |
|
static |
|
10.2.0.0/16 |
Attachment ID for peering connection
|
static |
Customer gateway BGP table
The customer gateway BGP table contains the following VPC CIDRs.
-
10.0.0.0/16
-
10.2.0.0/16
