How to Choose Between VGW and TGW for AWS Site-to-Site VPN Routing

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Sure! Here’s a clear, simple, and human-friendly version of the content rephrased as a How-To blog, focusing on a solution using transitive routing options for AWS Site-to-Site VPN.

If you’re setting up a secure connection between your on-premises network and AWS, you might be wondering how to get your VPN routing just right. Transitive routing is key here—it allows your traffic to travel through multiple networks without needing a direct connection between every pair. Let’s go over how to choose the best routing option for your setup, especially when using a Virtual Private Gateway (VGW) in AWS.

When you connect your on-premises network to AWS, you typically have two main options for routing: using static routes or dynamic routing protocols like Border Gateway Protocol (BGP).

A Virtual Private Gateway (VGW) is often used to connect your on-premises network to AWS. It acts as the point of entry for your VPN connection. To enable transitive routing—where traffic from one network can reach a third network through AWS—your routing setup needs to support it.

Here’s how you can set it up:

Use Dynamic Routing with BGP
BGP makes managing routes easier. It allows your networks to automatically exchange routing information. When you configure BGP on your VPN connection, AWS learns your on-premises network routes, and your on-premises router learns AWS subnets. This setup makes transitive routing possible because the routing information is shared dynamically.
Configure Your Router Correctly
Make sure your on-premises router supports BGP and is configured to advertise your internal subnets to AWS. Also, ensure AWS is set to advertise the subnets associated with your VGW. Properly configured BGP peering allows traffic from other networks to flow through AWS to reach your desired destination.
Check Your AWS Route Tables
In AWS, update your route tables to point traffic destined for other networks through the Virtual Private Gateway. You need to add routes for any networks that should be reachable via your VPN connection.
Test Connectivity
After setting everything up, test the connection to ensure traffic flows smoothly through routes. You might need to verify that the routing tables have the correct entries and that BGP sessions are established successfully.

In summary, using BGP with your Virtual Private Gateway and configuring your routers properly is the best way to enable transitive routing in your AWS VPN setup. This approach ensures your networks are interconnected without the need for multiple separate VPN connections, making your network management simpler and more efficient.

Let me know if you need more detailed steps on configuring BGP or specific router settings!