ovpn-dco VS openvpn-gui

We also back several OpenVPN related drivers, such as tap-windows6 driver, ovpn-dco-win driver, ovpn-dco linux kernel module. The tap-windows6 driver is the old Windows driver, which gives a pretty basic tun/tap interface. The DCO drivers are the next generation drivers, where more of the cryptographic operations are moved into the OS kernel instead of happening inside the OpenVPN Core components; which has the potential to improve the tunnel performance.

With Linux, there's lots of stuff going on in the OpenVPN community, in particular with a kernel module to accelerate the performance. The OpenVPN 3 Linux client already supports it and the coming OpenVPN 2.6 release (currently in development) will add support for both server and client mode with data channel offload (aka DCO).

Here is link number 1 - Previous text "DCO"

All that said, with the work being done in OpenVPN with the Data Channel Offload (DCO), it would probably be easier to get hardware support. The DCO implementations (ovpn-dco, ovpn-dco-win) offloads the data channel crypto operations to the virtual network driver, so the encryption/decryption/packet authentication happens entirely in the kernel space - which results in a noticeable performance boost. The tasks these DCO drivers does should be possible to more easily implement inside some dedicated hardware. But it won't be cheap.

There are work in progress on a OpenVPN kernel module, which will improve OpenVPN performance considerably: https://gitlab.com/openvpn/ovpn-dco

I use OpenVPN frequently for work and the OpenVPN GUI client since forever has an annoying bug (Which is that with Windows with multiple keyboards layouts, especially Arabic, upon connecting with OpenVPN the Windows language will switch to the second rtl language) that they don't plan to fix (check this and this).

It is likely an issue with the 'cipher' options, if any, that are in your ".opvn" file. This is telling you that the opvn setting is not finding a matching cipher it is allowed to use. The fix per the message would be to add the Servers cipher to your options. https://github.com/OpenVPN/openvpn-gui/issues/381 https://github.com/OpenVPN/openvpn/blob/master/doc/man-sections/cipher-negotiation.rst

The big downside of the mobile SSL VPN solution (which is basically OpenVPN) is, you can not establish a vpn connection before the windows login. So Windows Group Policies are not applied immediatly and the user needs to manually connect to the VPN after the login. If OpenVPN would provide such a solution I would switch back to SSL VPN. There is still a feature request on Github since 2016 for this feature. See here: https://github.com/OpenVPN/openvpn-gui/issues/77

In addition we back several other open source projects, such as the OpenVPN GUI, OpenVPN for Android and OpenVPN 3 Linux ... these all provide various user interfaces on top of the OpenVPN Core component.