We created an external data source using Lightning connect for oData 2.0 to our SAP Gateway System. We use a reverse proxy that allows access from the cloud. However we get the error "The external system is unreachable. Make sure that the URL is correct in the external data source settings, and that the server's SSL certificate is valid for its domain name. Attempted to reach this URL: xxxx".
We added the host to the remote site settings, made the service anonymous all to no avail. Debug trace gives no information. The only issue we can think of is that we use internal PKI and not a paid certificate on our development systems. Could this be the issue? Can we import a CA Certificate and make it trusted in Salesforce?