I can no longer connect to Fortigate.

Question

I'm not sure if it's due to a Windows update, but I can no longer connect to the VPN on Fortigate. If you have any idea what might be causing this, please let me know. Internet access through a browser works without any problems.

Answer 1

Hi,

Thank you for sharing your question. I understand how confusing and worrying it is when your VPN suddenly stops working, especially when everything else on the internet still works normally.

Based on Microsoft’s documented cases, Fortigate and similar VPN clients often stop working after certain Windows updates because the update changes Windows’ networking components, firewall behavior, or VPN driver compatibility.

In many reported situations, the VPN appears to connect but cannot pass any internal traffic, or it fails during connection attempts, which aligns with known Windows update issues affecting VPN routing. Some users regain VPN access by updating Windows fully, repairing or reinstalling the FortiClient VPN, or removing conflicting security software that blocks the VPN tunnel after an update.

If the issue began immediately after a recent cumulative update, removing or rolling back the update temporarily has also been shown to restore VPN connectivity but only as a workaround.

Did the VPN stop working right after a Windows update, or did you install any new security or antivirus software recently?

Feel free to share what happened right before the issue started  I can then guide you through the quickest, safest steps to get your Fortigate VPN working again.

I hope this helps.

Best Regards,

Noel

Answer 2

The Fortigate VPN connectivity loss after a Windows update is commonly related to changes in Windows networking, VPN stack, or security components. Since browser Internet access still works, focus on VPN-specific causes.

Try these targeted checks and fixes on the Windows client:

1. Check for multiple VPN clients or drivers
   If more than one VPN product is installed (FortiClient plus others), Windows can fail to route VPN traffic correctly.

• Uninstall any unused VPN clients.
• Reboot and test Fortigate VPN again.

This aligns with a known issue where multiple VPN applications on one client prevent VPN traffic from passing correctly.

2. Update Windows and security components
   Install all pending Windows Updates, including cumulative and security updates. Some VPN issues are fixed by specific rollups or platform updates.

• Go to Settings → Windows Update → Check for updates and install everything offered.
• Reboot and test the VPN.

If Microsoft Defender is in use and Network Protection or Exploit Guard was recently enabled by policy, make sure the Defender platform is fully updated. An outdated Defender platform can break VPN connectivity until updated.

3. Temporarily disable or remove third‑party security software
   Third‑party antivirus or endpoint security can interfere with VPN tunnels after an update.

• Temporarily disable or uninstall third‑party AV/firewall.
• Reboot and test Fortigate VPN.
  If VPN works afterward, adjust or update that security product.

4. Check if only VPN traffic is broken
   Once connected (or attempting to connect):

• Try to ping a known internal IP over the VPN.
• If ping returns General failure or similar while normal Internet still works, suspect Defender Network Protection or another filter driver blocking VPN traffic.

If Defender Network Protection was recently enabled and you suspect it:

• Ask the administrator to either update Defender to the latest platform version or set the Network Protection policy to Not Configured as a test.

5. Reinstall or repair the FortiClient VPN
   If the problem started immediately after a Windows update, the FortiClient drivers or services may need repair.

• Uninstall FortiClient completely.
• Reboot.
• Install the latest FortiClient version supported by the Fortigate firmware.
• Reboot again and test.

6. If using Wi‑Fi, test on wired and with a stable signal
   Unstable Wi‑Fi can break third‑party VPN connections when Windows mismanages routes.

• Test the VPN over a wired Ethernet connection if possible.
• If VPN works on wired but not on Wi‑Fi, update Wi‑Fi drivers and Windows, then test again.

7. If nothing helps
   Provide the Fortigate/IT admin with:

• Exact Windows version and recent update history.
• FortiClient version.
• Exact error message or code from FortiClient.
  They can then check Fortigate logs and confirm whether the connection reaches the gateway or is blocked on the client.

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References:

• You can't connect to the Internet after you connect to a VPN server
• Lost internet connectivity using VPN in Windows Defender Exploit Guard - Network Protection
• No VPN traffic passes through a VPN client in Windows 8.1 or Windows Server 2012 R2
• VPN connection cannot be established when you use a Wi-Fi connection in Windows 8.1 or Windows 8
• Third-party VPN client stops Internet connectivity in Windows 7 SP1 or Windows Server 2008 R2 SP1