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How to workaround the VPN error ‘Unable to establish the VPN connection . The VPN server may be unreachable. (-5052)’

By: Author Alex Lim

Posted on

Categories Troubleshooting

This article describes how to process when having an issue with the FortiClient connectivity to FortiaGte or FortiSASE.

Scope

FortiClient, FortiGate, FortiSASE

Solution

On some Windows machines, the user might have the error ‘Unable to establish the VPN connection. The VPN server may be unreachable. (-5052)’ while trying to connect to the FortiGate or FortiSASE using the FortiClient VPN.

On some Windows machines, the user might have the error 'Unable to establish the VPN connection. The VPN server may be unreachable. (-5052)' while trying to connect to the FortiGate or FortiSASE using the FortiClient VPN.

Run the basic connectivity steps

  1. Verify network connectivity.
  2. Check VPN server settings in FortiClient.
  3. Disable firewall and antivirus temporarily.
  4. Update FortiClient to the latest version.
  5. Flush the DNS cache using the command ‘ipconfig /flushdns’.
  6. Remove any conflicting VPN or networking software.

Isolate the cache issues

  1. Renamed the folder C:\Users\<user>\AppData\Local\FortiClient with a name.
  2. Re-connect the FortiClient to the Fotigate or FortiSASE (FortiClient will automatically create a new folder C:\Users\<user>\AppData\Local\FortiClient)

Note: At step number 1, the user can delete the file at all. However, it is recommended to rename it and keep it for further analysis or rolling-back, if needed.

If the issue persists, contact Fortinet support for further assistance.