A company is planning to migrate to AWS and use multiple VPCs in multiple AWS Regions. A network engineer must connect the eu-west-1 and eu-central-1…

The configuration is missing the necessary routes in the VPC subnet route tables. For an EC2 instance within a VPC to send traffic to a destination outside of its VPC CIDR range (like the remote VPC), its subnet route table must have a route directing that traffic to the Transit Gateway. The engineer needs to add a route in the route tables for the subnets in Prod A (10.0.0.0/16) for the destination CIDR of Prod B (10.1.0.0/16), with the target set to the local Transit Gateway. A similar route is needed in Prod B's subnet route tables for Prod A's CIDR. A summarized route like 10.0.0.0/8 would cover both and is a valid approach.

A. A peering attachment is a logical construct for routing between Transit Gateways; it does not have a modifiable IP address in this context.
B. For Transit Gateway peering, static routes pointing to the peering attachment are required in the Transit Gateway route tables. Route propagation does not work across a peering connection.
D. The production accounts do not own the Transit Gateway route tables; they are managed in the networking account. The issue is not with TGW routing but with VPC-level routing.

1. AWS Documentation. (2023). Routing for a transit gateway. "You must add a route to your subnet route tables to send VPC traffic to the transit gateway."

2. AWS Documentation. (2023). Transit gateway peering attachments. "To send traffic to the peer transit gateway, you must add a static route to the transit gateway route table that points to the transit gateway peering attachment."

3. AWS Documentation. (2023). Example: Inter-Region peering. "Update the VPC route table... For Destination, enter the CIDR block of the peer VPC. For Target, select the transit gateway." (This is shown in the routing configuration examples).