Multiple Transit Gateway Route Tables and Direct Connect Gateway Attachment

0

Hello AWS Community,

I am currently managing a network architecture with 30+ VPCs/accounts following a hub-and-spoke design. Currently, we have a single Transit Gateway (TGW) with one route table (RTB), and we are utilizing Direct Connect Gateway (DXGW) attachment for propagating routes from on-premises to connect multiple VPCs.

Our requirement now is to have multiple TGW route tables, one for each VPC. However, I am unsure about how to proceed with attaching the DXGW attachment to all the route tables if we maintain multiple TGW route tables.

Can someone please confirm whether it's possible to attach a DXGW attachment to multiple TGW route tables simultaneously? If not, what would be the recommended approach to achieve our requirement?

Thank you in advance for your guidance and assistance.

2 Answers
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Accepted Answer

Clarifying a few terms so that it aligns with our documentation:

  • Attachment: This is where you connect something (VPC, Direct Connect Gateway, VPN, etc.) to Transit Gateway.
  • Association: Each attachment can have a single route table associated with it.
  • Propagation: This is how a route table "learns" routes. Propagation can be automatic or you can manually assign static routes to route tables.

While you can have a route table for each VPC I would question whether that is a good idea or not - it can be a lot of extra work. If you were trying to set up an environment where the VPCs cannot communicate with each other but can communicate with your on premises network via Direct Connect then you can do that using only two route tables - one for the VPCs and one for the Direct Connect Gateway attachment.

However, to answer your question specifically: You don't need to attach Direct Connect Gateway to multiple route tables; you want to propagate the routes for your on premises network (which are reachable via Direct Connect and Direct Connect Gateway) to all the route tables which are associated with the VPC attachments. You can absolutely do that.

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Hello.

Is your request to set up the configuration as described in the document below?
https://docs.aws.amazon.com/whitepapers/latest/hybrid-connectivity/aws-dx-dxgw-with-aws-transit-gateway-multi-regions-more-than-3.html

In that case, I think you could select multiple Transit Gateways when linking DirectConnect Gateway and Transit Gateway using the document below.
https://docs.aws.amazon.com/directconnect/latest/UserGuide/direct-connect-transit-gateways.html

If you link multiple Transit Gateways to DirectConnect Gateway, corresponding attachment will be created.
So, by linking that attachment to each TransitGateway route table, it will be routed to the DirectConnect Gateway.

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