AWS Site to Site VPN is not up and running

To troubleshoot your AWS Site-to-Site VPN tunnel that is not coming up between your Singapore and US West Oregon subscriptions, there are several steps you can take:

1. Check your VPN configuration:

   • Ensure that the VPN connection settings on both sides (Singapore and US West Oregon) are correctly configured and match each other.
   • Verify that the customer gateway and virtual private gateway configurations are correct.

2. Review firewall rules:

   • Make sure that the necessary firewall rules are in place on both sides to allow VPN traffic.
   • Check if there are any security groups or network ACLs blocking the VPN traffic.

3. Examine routing:

   • Verify that the route tables in both VPCs are correctly configured to route traffic through the VPN connection.
   • If you're using BGP, ensure it's properly configured on both ends.

4. Check for overlapping IP ranges:

   • Ensure that the IP address ranges of your VPCs in Singapore and US West Oregon do not overlap.

5. Verify tunnel settings:

   • Check the IKE (Internet Key Exchange) and IPsec settings to ensure they match on both sides.
   • Look for any Phase 1 or Phase 2 mismatches in the VPN configuration.

6. Monitor VPN logs:

   • Enable CloudWatch logging for your VPN connection and examine the logs for any error messages or issues.

7. Check for packet loss:

   • There might be packet loss over the connection. You can use tools like ping or traceroute to test connectivity.

8. Verify customer gateway device:

   • If you're using a hardware device as your customer gateway, ensure it's compatible with AWS and properly configured.

9. Consider using the AWS VPN configuration files:

   • Download and use the example configuration file that corresponds to your customer gateway device to ensure proper setup.

If after checking these items the tunnel is still down, you may need to engage AWS support for further assistance. They can help you dive deeper into the specific configuration and logs to identify the root cause of the issue.
Sources
Troubleshoot VPN routing issues | AWS re:Post
Troublehsoot connectivity between SIte-to-Site VPN and VPC | AWS re:Post
Connection to on-prem not working when both site-to-site VPN is active | AWS re:Post