AdrianG001
The error "Unknown error communicating with Duo" implies that the OpenVPN machine is unable to reach Duo on port 443. This error typically occurs after passing primary authentication in OpenVPN Access Server for one of the following reasons:
A firewall issue preventing connectivity.
To resolve this, ensure that port 443 is open on your firewall. In addition, please reference our list of Duo's IP ranges for whitelisting.
Incompatible client version.
To resolve, make sure you are using OpenVPN client version 2.2 or higher.
Wrong entry for ikey, skey, or api host.
Using " instead of ' will trigger a mismatch and not allow authentication.
Hope this helps.
