Troubleshooting Tip: Fix 'Unable to connect to VPN because tunnel configuration is unsupported' error for dial-up IPsec connections

[Ade_23]

Description	This article describes what changes to make to fix the error 'Unable to connect to VPN because tunnel configuration is unsupported' when connecting to IPsec VPNs from a MacOS device.
Scope	FortiClient (MacOS) 7.4.2.
Solution	When connecting to a dial-up IPsec VPN tunnel from a MacOS device, the following error may be encountered: This error is because FortiClient on MacOS does not support DH group values above 18 for ikev1 configurations. For FortiClient version 7.4.2, the default DH group value is 20 which is unsupported for MacOS. To resolve this, a value of 18 or lower simply needs to be chosen. An example is provided below. On FortiClient, navigate to Remote Access, then edit the connection using the icon  beside the VPN Name. Next, select VPN Settings and expand Phase 1 and Phase 2 to make the changes similar to the image below. In FortiClient version 7.4.3, the default has been set to DH group 5 for IKEv1 to avoid this issue.