C# FTPS FtpWebRequest set passive mode to use port range

Question

I am not able to connect to a specific FTP using C# FtpWebRequest.

With TotalCommander or FileZilla I am able to connect.

Information about FTP say:

FTPS – implicit SSL/TLS
Port 990
Range of passive ports: 60000–60100

Another FTP works well.

var remoteFile = "ftp://ADDRESS:990/FILE.csv";
var localFile = Server.MapPath("~/tmp/file.csv");

int bufferSize = 2048;

if (!Directory.Exists(Path.GetDirectoryName(localFile)))
    Directory.CreateDirectory(Path.GetDirectoryName(localFile));
/* Create an FTP Request */
FtpWebRequest ftpRequest = (FtpWebRequest)FtpWebRequest.Create(remoteFile);
/* Log in to the FTP Server with the User Name and Password Provided */
ftpRequest.Credentials = new NetworkCredential("USER", "PWD");
/* When in doubt, use these options */
ftpRequest.UseBinary = true;
ftpRequest.UsePassive = true;
ftpRequest.KeepAlive = true;

ftpRequest.EnableSsl = true;
// Always returns true
ServicePointManager.ServerCertificateValidationCallback = OnValidateCertificate; 

/* Specify the Type of FTP Request */
ftpRequest.Method = WebRequestMethods.Ftp.DownloadFile;
/* Establish Return Communication with the FTP Server */
FtpWebResponse ftpResponse = (FtpWebResponse)ftpRequest.GetResponse();
/* Get the FTP Server's Response Stream */
Stream ftpStream = ftpResponse.GetResponseStream();
/* Open a File Stream to Write the Downloaded File */
FileStream localFileStream = new FileStream(localFile, FileMode.Create);
/* Buffer for the Downloaded Data */
byte[] byteBuffer = new byte[bufferSize];
int bytesRead = ftpStream.Read(byteBuffer, 0, bufferSize);
/* Download the File by Writing the Buffered Data Until the Transfer is Complete */
try
{
    while (bytesRead > 0)
    {
        localFileStream.Write(byteBuffer, 0, bytesRead);
        bytesRead = ftpStream.Read(byteBuffer, 0, bufferSize);
    }
}
catch (Exception ex)
{
    Console.WriteLine(ex.ToString());
}
/* Resource Cleanup */
localFileStream.Close();
ftpStream.Close();
ftpResponse.Close();
ftpRequest = null;

In my opinion the error is caused by passive port range 60000–60100. But I don't know how to set it up.

Martin Prikryl Martin Prikryl · Accepted Answer · 2019-07-02T13:05:49

The FTP passive port range is a server-side configuration.

You do not set the passive port range on client side – FileZilla nor Total Commander do not have such configuration option either. FTP client uses the port chosen by the server.

Your actual problem is rather that .NET/FtpWebRequest does not support implicit TLS/SSL:
Does .NET FtpWebRequest Support both Implicit (FTPS) and explicit (FTPES)?

C# FTPS FtpWebRequest set passive mode to use port range

2 Answers