A company has BU-1 and BU-2 business units. Each BU has two VPCs in us-east-1 and one VPC in ap-south-1. Resources must communicate within the same BU but must be isolated from other BUs. The company will add more BUs and expand into additional Regions. Which design meets these requirements with the highest operational efficiency?

The correct option leverages AWS Cloud WAN's segmentation capabilities effectively. By creating a separate Cloud WAN segment for each Business Unit (BU) and attaching all of a BU's VPCs to its dedicated segment, you inherently achieve isolation between BUs. Cloud WAN segments are designed to isolate network traffic, ensuring that resources in one BU's segment cannot communicate with resources in another BU's segment unless explicitly allowed. This design scales well as new BUs and Regions are added, as you simply create new segments and attach resources. The incorrect options either introduce unnecessary complexity or do not fully utilize Cloud WAN's isolation features. Using transit gateways requires manual peering and complex route table management across multiple regions and BUs, which is less operationally efficient than Cloud WAN for this scale. While Cloud WAN can deny traffic between segments, creating distinct segments for each BU with default isolation is a more direct and operationally efficient approach than manually configuring segment actions or isolate-attachments for every segment, especially as the number of BUs grows.