Synology VPN Server TLS Handshake Errors: Troubleshooting and Fixes

So, you’re running a VPN Server on your Synology NAS, and it suddenly stops working? You’re not alone. Many users, myself included, have experienced frustrating TLS handshake timeout errors that bring the VPN to a screeching halt. The typical symptom? Clients can’t connect, and the only solution seems to be a full NAS reboot. Let’s dive into this issue and explore some potential solutions.

I’ve been running OpenVPN on my Synology DS918+ (DSM 7.2.1) and have encountered this problem several times. It’s incredibly disruptive, especially when you rely on your VPN for remote access.

The Problem: TLS Handshake Timeouts

The error usually appears as “TLS Error: TLS key negotiation failed to occur within 60 seconds (check your network connectivity)” on the client side. On the Synology NAS, the VPN Server logs might show “TLS Error: TLS handshake failed” and “SIGUSR1[soft,tls-error] received, process restarting.” You might also see connected clients listed as ‘UNDEF’ in the VPN connection list on the NAS.

Restarting the VPN Server package doesn’t help. Even manually killing the OpenVPN processes and restarting doesn’t always work. It really feels like a deeper issue within Synology’s VPN Server implementation.

Troubleshooting Steps

Before resorting to a full reboot, here are some troubleshooting steps you can try:

• Check Network Connectivity: Although the error message suggests checking your network, the problem is rarely on the client side if multiple clients and networks are affected. Still, it’s worth verifying that your NAS has a stable internet connection and that there are no temporary network hiccups.
• Update Your Synology NAS and VPN Server Package: Ensure your DSM and VPN Server package are running the latest versions. Sometimes, updates address underlying bugs that might cause these issues.
• Check Firewall Rules: Review your Synology firewall rules to confirm that the necessary ports for your VPN protocol (e.g., OpenVPN’s default port 1194) are open and accessible.
• Disable and Re-enable the VPN Server: While simply restarting the package often doesn’t work, try completely disabling the VPN Server, waiting a few minutes, and then re-enabling it. This can sometimes clear out problematic processes or configurations.
• Adjust MTU Settings: In some cases, incorrect Maximum Transmission Unit (MTU) settings can cause TLS handshake issues. Experiment with slightly lower MTU values on both your client and server to see if that improves stability.

The Nuclear Option: Rebooting

If all else fails, rebooting the entire NAS usually resolves the problem, at least temporarily. However, this isn’t a practical long-term solution.

Looking for a Permanent Fix

If you’ve also experienced this issue and found a more permanent solution, please share it in the comments! The Synology community needs to find a reliable fix for this frustrating problem.