Ftp.dll .NET FTP component supports both Active and Passive mode FTP transfers.

In Active mode client waits for incomming data connections, in Passive mode client establishes data connections.

Passive mode is default. You can switch to Active mode using Mode property:

// C#

using (Ftp client = new Ftp())
{
    client.Mode = FtpMode.Active;

    client.Connect("ftp.example.com");
    client.Login("user", "password");

    // ...

    client.Close();
}

' VB.NET

Using client As New Ftp()
    client.Mode = FtpMode.Active

    client.Connect("ftp.example.com")
    client.Login("user", "password")

    ' ...

    client.Close()
End Using

With Ftp.dll .NET FTP component establishing connection using default port is easy:

// C#

client.Connect("ftp.example.com");

' VB.NET

client.Connect("ftp.example.com")

If you need to specify different port just use overloaded version of Connect method:

// C#

client.Connect("ftp.example.com", 999);
// -or-
client.Connect("ftp.example.com", 999, false);

' VB.NET

client.Connect("ftp.example.com", 999)
' -or-
client.Connect("ftp.example.com", 999, False)

If you are using SSL:

// C#

client.ConnectSSL("ftp.example.com", 999);
// -or-
client.Connect("ftp.example.com", 999, true);

' VB.NET

client.ConnectSSL("ftp.example.com", 999)
' -or-
client.Connect("ftp.example.com", 999, True)

You can also specify the port range used in Active mode.

// C#

client.ActiveModePorts = new Range(1024, 1025);

' VB.NET

client.ActiveModePorts = New Range(1024, 1025)

You can set the IP address announced to the FTP server in Active mode data transfer.
By default, the value of this property is IPAddress.None which means that the address of the network interface is used instead.

// C#

client.ActiveModeAddress = IPAddress.Parse("ftp.example.com");

' VB.NET

client.ActiveModeAddress = IPAddress.Parse("ftp.example.com")

This blog post describes hot to check the file checksum (hash) after upload to FTP server. Ftp.dll .NET FTP component supports most popular hashing algorithms like CRC, MD5 and SHA1.

First add appropriate namespaces:

// C# version

using Limilabs.FTP.Client;
using Limilabs.FTP.Client.Hash;

' VB.NET version

Imports Limilabs.FTP.Client
Imports Limilabs.FTP.Client.Hash

Then upload the file, ask the server for hash of the uploaded file, compute the local hash and compare them:

// C# version

using (Ftp client = new Ftp())
{
    client.Connect("ftp.example.org");
    client.Login("user", "password");

    client.Upload("report.txt", @"c:\report.txt");

    byte[] serverHash = client.GetFileHash(
        "report.txt",
        FtpHashType.CRC);

    FileHash hash = new FileHash(FtpHashType.CRC);
    bool hashIsValid = hash.IsValid(@"c:\report.txt", serverHash);

    Console.WriteLine(hashIsValid);

    client.Close();
}

' VB.NET version

Using client As New Ftp()
	client.Connect("ftp.example.org")
	client.Login("user", "password")

	client.Upload("report.txt", "c:\report.txt")

	Dim serverHash As Byte() = client.GetFileHash( _
		"report.txt", _
		FtpHashType.CRC)

	Dim hash As New FileHash(FtpHashType.CRC)
	Dim hashIsValid As Boolean = hash.IsValid("c:\report.txt", serverHash)

	Console.WriteLine(hashIsValid)

	client.Close()
End Using

You can use CRC, MD5 and SHA1 algorithms for hash verification.

You can download Ftp.dll FTP/FTPS client for .NET here.

Most likely your FTP server requires explicit SSL. So first try to connect without SSL:

// C#

client.Connect("ftp.example.org");

' VB.NET

client.Connect("ftp.example.org")

Then, before logging-in, start explicit SSL negotiation:

// C#

client.AuthSSL();

' VB.NET

client.AuthSSL()

Now, your connection is secured.

Remember that you can ignore SSL certificate errors using ServerCertificateValidate event:

// C# version

using (Ftp client = new Ftp())
{
    // Use this line to validate self-signed certificates:
    client.ServerCertificateValidate += ValidateCertificate;

    client.Connect("ftp.example.org");
    client.AuthSSL();
    client.Login("username", "password");

    foreach (FtpItem item in client.GetList())
    {
        if (item.IsFolder == true)
            Console.WriteLine("[{0}]", item.Name);
        else
            Console.WriteLine("{0}", item.Name);
    }
    client.Close();
}

private static void ValidateCertificate(
    object sender,
    ServerCertificateValidateEventArgs e)
{
    const SslPolicyErrors ignoredErrors =
        SslPolicyErrors.RemoteCertificateChainErrors |
        SslPolicyErrors.RemoteCertificateNameMismatch;

    if ((e.SslPolicyErrors & ~ignoredErrors) == SslPolicyErrors.None)
    {
        e.IsValid = true;
        return;
    }
    e.IsValid = false;
}

' VB.NET version

Using client As New Ftp()
    ' Use this line to validate self-signed certificates:
    AddHandler client.ServerCertificateValidate, AddressOf ValidateCerificate

    client.Connect("ftp.example.org")
    client.AuthSSL()
    client.Login("username", "password")

    For Each item As FtpItem In client.GetList()
        If item.IsFolder = True Then
            Console.WriteLine("[{0}]", item.Name)
        Else
            Console.WriteLine("{0}", item.Name)
        End If
    Next
    client.Close()
End Using

Private Sub ValidateCerificate( _
    ByVal sender As Object, _
    ByVal e As ServerCertificateValidateEventArgs)

    Const ignoredErrors As SslPolicyErrors = _
        SslPolicyErrors.RemoteCertificateChainErrors Or _
        SslPolicyErrors.RemoteCertificateNameMismatch

    If (e.SslPolicyErrors And Not ignoredErrors) = SslPolicyErrors.None Then
        e.IsValid = True
        Return
    End If
    e.IsValid = False
End Sub

You can download Ftp.dll FTP/FTPS client for .NET here.

If you get “The remote certificate is invalid according to the validation procedure” exception while trying to establish SSL connection, most likely your server certificate is self-signed or you used incorrect host name to connect (Host name must match the name on certificate, for example ftp.example.com and example.com may point to the same server, but certificate is issued only to ftp.example.com and this is the address you should use).

Good news is that you can accept self-signed certificates using Ftp.dll FTP and FTPS .NET component.

First you need to subscribe to ServerCertificateValidate event.

Then you need to create ValidateCertificate method that validates the certificate (ignores certificate chain and name mismatch errors).

// C# version

using (Ftp client = new Ftp())
{
    // we will use custom validation
    client.ServerCertificateValidate +=
        new ServerCertificateValidateEventHandler(Validate);

    // Minimalistic version to accept any certificate:
    //client.ServerCertificateValidate += 
    //    (sender, e) => { e.IsValid = true; };

    client.ConnectSSL("ftp.example.org");
    client.Login("username", "password");

    foreach (FtpItem item in client.GetList())
    {
        if (item.IsFolder == true)
            Console.WriteLine("[{0}]", item.Name);
        else
            Console.WriteLine"{0}", item.Name);
    }
    client.Close();
}

private static void ValidateCertificate(
    object sender,
    ServerCertificateValidateEventArgs e)
{
    const SslPolicyErrors ignoredErrors =
        SslPolicyErrors.RemoteCertificateChainErrors |  // self-signed
        SslPolicyErrors.RemoteCertificateNameMismatch;  // name mismatch

    if ((e.SslPolicyErrors & ~ignoredErrors) == SslPolicyErrors.None)
    {
        e.IsValid = true;
        return;
    }
    e.IsValid = false;
}

' VB.NET version

Using client As New Ftp()
    ' Use this line to validate self-signed certificates:
    AddHandler client.ServerCertificateValidate, AddressOf ValidateCerificate

    client.ConnectSSL("ftp.example.org")
    client.Login("username", "password")

    For Each item As FtpItem In client.GetList()
        If item.IsFolder = True Then
            Console.WriteLine("[{0}]";, item.Name)
        Else
            Console.WriteLine("{0}", item.Name)
        End If
    Next
    client.Close()
End Using

Private Sub ValidateCerificate( _
    ByVal sender As Object, _
    ByVal e As ServerCertificateValidateEventArgs)

    Const ignoredErrors As SslPolicyErrors = _
        SslPolicyErrors.RemoteCertificateChainErrors Or _    ' self-signed
        SslPolicyErrors.RemoteCertificateNameMismatch        ' name mismatch

    If (e.SslPolicyErrors And Not ignoredErrors) = SslPolicyErrors.None Then
        e.IsValid = True
        Return
    End If
    e.IsValid = False
End Sub

You can download Ftp.dll FTP/FTPS component for .NET here.