This is a fairly generic message that originates from a communication problem between InControl client and server. The message is generic because the client does not know what went wrong as the connection attempt was abruptly closed, but the client does not know why the connection was closed. Then this fairly generic message is shown to to the administrator in the InControl client.
The InControl server log may contain more information about what the connection problem is/was. The default path to the InControl server log is the following:
- The server determined that it did not support any of the ciphers that the client offered, and then it resorted to closing the connection. This will be shown fairly clearly in the InControl server logs if this is the case.
- Was the default allowed ciphers in Windows (client side) changed or disabled? If the default ciphers was changed it could cause compatibility issues (not just with InControl but other programs as well).
- For names of the cipher suites in Windows, there's no standard. The MS documentation needs to be carefully be consulted for what they are named in order to configure it in Windows. Additionally, there is a chance that MS have renamed some of the ciphers between some versions of Windows. It's quite complex to setup up correctly. If these settings/ciphers are changed, the MS documentation must be carefully consulted.
- Very unstable network connection
- Unlikely, but possible.
There may be other reasons as well, a good starting point would be to check the InControl server log if you see anything about the failed connection attempt. If the log is blank or does not contain any entry that matches the connection attempt (time wise) it is most likely one of the two first points.
For more information about how a TLS connection works, this page illustrates it very good with every byte explained and reproduced: https://tls12.xargs.org/
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