The underlying connection was closed. The server committed a protocol violation

Question

I am trying to get the directory list of a FTPS FileZilla server using the code below :

ftpRequest = (FtpWebRequest)FtpWebRequest.Create(host + "/" + directory);
ftpRequest.EnableSsl = true;

ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(ValidateCertificate);
ftpRequest.Credentials = new NetworkCredential(user, pass);
ftpRequest.UseBinary = true;
ftpRequest.UsePassive = true;
ftpRequest.KeepAlive = true;
ftpRequest.Method = WebRequestMethods.Ftp.ListDirectory;
ftpResponse = (FtpWebResponse)ftpRequest.GetResponse();

I got an exception when FtpWebResponse)ftpRequest.GetResponse() is executed :

the underlying connection was closed. The server committed a protocol violation.

When I switch to normal FTP connection. Everything works correctly.

Did I miss something to establish this FTPS connection ? thanks for help

Answer 1

Implicit FTPS is not supported by the FtpWebRequest class (see here).

When EnableSsl is set to true, it actually triggers an AUTH TLS command to the server, asking to start an Explicit FTPS session.

In your case, you have to configure Filezilla Server to use Explicit FTPS. The procedure is documented on Filezilla Wiki