A company has agreed to collaborate with a partner for a research project. The company has multiple VPCs in the us-east-1 Region that use CIDR blocks within 10.10.0.0/16. The VPCs are connected by a…

Creating a new VPC with a third-party router and then sharing existing TGWs introduces significant complexity, additional costs, and is far from a 'minimum changes' solution.

While IPsec VPN connections can connect networks, creating an IPsec VPN between two Transit Gateways in the same region is less efficient and more complex than using Transit Gateway peering, which is specifically designed for TGW-to-TGW connectivity.

Configuring a cross-account Transit Gateway peering attachment between TGW-C and TGW-P is the native AWS solution for connecting two Transit Gateways in the same or different AWS Regions. This approach directly links the two TGWs, allowing their attached VPCs to communicate with minimal configuration changes (creating the attachment and updating TGW route tables) and is designed for high efficiency and scalability.

Sharing TGW-C with the partner account via AWS Resource Access Manager (AWS RAM) would allow the partner's VPCs to attach directly to TGW-C, bypassing their existing TGW-P. This would force the partner to restructure their network, contradicting the 'minimum changes' requirement for *both* networks.