Issue with Setting up VPN Connection between UTM Sophos Firewall V9 and AWS VPC

Question

Hey everyone,

I've been trying to set up a VPN connection between my UTM Sophos Firewall V9 and AWS VPC, but I've run into some issues. I hope someone can help me troubleshoot this problem.

Here's what I've done so far:

In the AWS console, I created a VPN connection with dynamic routing, specifying the appropriate VPC and subnets.

On the UTM Sophos Firewall V9 side, I added the AWS IAM credentials, including the access key and secret access key.

I downloaded the VPC configuration file from the VPN connection page in AWS, specifically tailored for the UTM Sophos Firewall V9 vendor.

Now, here's the issue I'm encountering:

The VPN tunnels are successfully established on both the UTM Sophos Firewall V9 and AWS VPC sides. However, when I try to ping resources across the VPN, I'm not receiving any response.

To further investigate, I've checked the firewall rules on both the AWS and Sophos Firewall sides, and they appear to be correctly configured. I ensured that the necessary traffic is allowed through the firewall rules for the VPN connection. I've checked the route tables as well, and they are correctly configured.

At this point, I'm uncertain about what could be causing the lack of response to the ping requests. I'm wondering if there are additional settings or configurations that need attention to resolve this issue.

If anyone has experience with setting up a VPN connection between UTM Sophos Firewall V9 and AWS VPC, I would greatly appreciate any insights, suggestions, or troubleshooting tips you can provide. What else can I check or configure to enable successful communication over the VPN?

Thank you in advance for your assistance!

Accepted Answer

You can enable VPC flow logs and then see if the ICMP traffic is reaching that EC2, if you see the traffic there then and if it's been allowed (You would see that in the VPC flow logs), then make sure there is return traffic in the VPC flow logs.

Here is how to enable VPC flow logs https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs.html

1. If you don't see traffic reaching the EC2, then make sure of the routing on your  Sophos Firewall has a route to send traffic to AWS. 
2. If you see the traffic is reaching the EC2, if it's being denied then make sure to allow the traffic in the security group.
3. If you see the traffic is reaching the EC2, and is being allowed but no return traffic, then make sure of the subnet route table that it has a route for your on-prem CIDR pointed to the Virtual gateway/ or the Transit Gateway.

A few other points, make sure you're not running into multiple security associations issue https://repost.aws/knowledge-center/vpn-connection-instability
If you're using transit gateway, then make sure you have a route for on-prem in the TGW route table.

Issue with Setting up VPN Connection between UTM Sophos Firewall V9 and AWS VPC

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