Enabling Secure Communication Across Multiple VPCs with a Single VPN Connection

Introduction: In the complex landscape of cloud infrastructure, efficiently managing communication between Virtual Private Clouds (VPCs) is paramount. This blog post addresses a common query: "How can I allow communication between multiple VPCs from a single VPN connection attached to my transit gateway, without allowing access between the VPCs?" We'll guide you through a comprehensive solution to establish network connectivity while maintaining a secure and controlled environment.

Step-by-Step Guide: Establishing Network Connectivity

1. Create a Transit Gateway and Attach VPCs:

• Utilize the Amazon VPC console to create a transit gateway.

• Attach your VPCs to the transit gateway, ensuring the Default association route table setting is turned off.

• Open the Amazon VPC console.

• Navigate to "Transit gateways" in the navigation pane.

• Choose "Create Transit Gateway" and provide the necessary details.

• Ensure to turn off the "Default association route table" setting.

• Once created, choose your transit gateway, navigate to the "Attachments" tab, and attach your VPCs.

2. Set Up a Site-to-Site VPN Connection:

• Establish a site-to-site VPN connection and attach it to your transit gateway.

• Choose the Dynamic Routing option for automatic VPN route propagation (requires Border Gateway Protocol).

• In the Amazon VPC console, navigate to "VPN Connections."

• Choose "Create VPN Connection" and select "Transit Gateway" as the target.

• Provide the required details, including the transit gateway ID and routing options.

• Choose "Create VPN Connection" and note the VPN connection details.

3. Configure Transit Gateway Route Tables:

• Create two transit gateway route tables (Route Table A and Route Table B) using the Amazon VPC console.

• Associate Route Table A with your VPCs, ensuring the Default association route table setting is disabled.

• Navigate to "Transit gateway route tables" in the Amazon VPC console.

• Choose "Create transit gateway route table" and name it "Route Table A."

• Associate it with your transit gateway.

• Repeat the process to create "Route Table B."

4. Associate Route Tables and VPN Connections:

• In "Transit gateway route tables," select "Route Table A."

• Choose "Associations" and create associations with your VPCs.

• Delete the VPN association from the default transit gateway route table.

• Select "Route Table B" and associate it with the VPN connection.

5. Propagate Routes for Comprehensive Connectivity:

• Propagate routes from VPCs and the VPN connection to both route tables.

• Ensure dynamic routes for the VPN connection in Route Table A and all VPCs in Route Table B.

• In "Transit gateway route tables," select "Route Table A."

• Choose "Actions," then "Create propagation."

• Propagate routes from the VPN to Route Table A.

• Repeat the process for "Route Table B," propagating routes from VPCs to Route Table B.

6. Configure Route Tables for On-Premises Connectivity:

• Define routes in the route table attached to the attachment subnet for on-premises connectivity.

• Routes are based on the destination subnet of the on-premises network, targeting the transit gateway.

• Navigate to "Route tables" in the Amazon VPC console.

• Choose the route table attached to the attachment subnet.

• In the "Routes" tab, choose "Edit routes."

• Add a route for the destination subnet of the on-premises network, targeting your transit gateway.

• Save the routes.

7. Additional Considerations for Restrictive Access:

• If necessary, create separate route tables for each VPC to implement more restrictive access.

• Keep in mind that transit gateway route table routing is based on associations, allowing flexibility in configuring routes.

• If necessary, create separate route tables for each VPC in "Transit gateway route tables."

• Configure routes based on your requirements for each VPC.

• Keep in mind that routing in transit gateway route tables is based on associations.

Conclusion:

By following these detailed steps, you can seamlessly enable communication between multiple VPCs and on-premises networks using a single VPN connection attached to a transit gateway. This solution strikes a balance between connectivity and security, ensuring that on-premises users can access resources across VPCs while maintaining strict isolation between VPCs. Implementing this approach enhances network architecture efficiency within the AWS ecosystem.

Embrace the power of AWS networking capabilities and streamline your cloud infrastructure for optimal performance and security.