FastConnect or Site-to-Site VPN connection to each region: This establishes the physical connection between your on-premises network and each OCI region, allowing for routing communication. It is essential for setting up the routing path.
Dynamic Routing Gateway (DRG) attached to each VCN: Each DRG acts as a central hub for routing traffic within its region. It receives routes from the FastConnect/VPN, learns routes from the attached VCNs, and propagates relevant routes to other DRGs. It plays a crucial role in routing decisions and traffic forwarding.
Route propagation and peering configuration between DRGs: This enables the DRGs to exchange routing information about the on-premises network and the target VCNs in different regions. By configuring peering and route filters, you control how routes are shared and advertised, ensuring secure and efficient traffic flow. This configuration is vital for the DRGs to communicate and direct traffic across regions.
Internet Gateway (IGW): An IGW provides public internet access within a VCN. However, transitive routing between private networks, including your on-premises network and OCI VCNs, focuses on private connectivity without accessing the public internet. Therefore, IGWs are not required for this specific setup.
In summary, while IGWs provide valuable functionalities within OCI VCNs, they are not part of the core resources needed for establishing private transitive routing between your on-premises network and different OCI regions. Remember, transitive routing utilizes dedicated gateways like DRGs for internal and private communication, not internet-facing resources like IGWs.