FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
This article describes how to resolve the issue of SSL Connection error 'Unable to establish the VPN connection. The VPN server may be unreachable (-20101)' and the connection fails at around 91%.
Scope
SSL VPN, FortiGate, FortiClient, Windows 10.
Solution
In case the SSL VPN Connection fails at almost 91% and the error is 'Unable to establish the VPN connection. The VPN server may be unreachable (-20101)', follow these steps:
If the SSL VPN Connection is successful using web mode:
In most cases, the root cause is that the Windows client machine is being utilized consistently for a long time without restart/closure, OR the machine slept/resumed some number of times:
Restart FortiSSLVPN demon (Services.MSC).
Restart FortiSSLVPN Client.
If the issue persists, check if the FortiClient is a trial/free version. Try re-installing the FortiClient and test the connection. Most probably, it should work.
If it still does not work, try re-installing Windows on the client machine.
If the issue is still not resolved, it is recommended to use the upgraded version of FortiClient.
