Socket class, connect to an endpoint with port 21

[Diego Escalona]

Hello everybody,

I'm developing a FTP Client using the socket class. Here is the code I use
to declare the socket:

Socket FTP_Socket = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);

I've developed other applications (not with the port 21) with sockets and to
verify the connection I always use the Socket.Connected var. In this case I
noticed that there was a problem because the FTP_Socket always connects
(gets Connected var true) to the remote Endpoint. It doesn't mind the IP
Address, it always connects if the remote Endpoint uses the port 21. In
order to verify that, I've developed a little tool that makes simple socket
connections and I always obtain the same results, it connects to any IP
Address (they can be not real) if I use the port 21.

Here is the code I use to connect with my little tool:

private void connect()
{
try
{
FTP_Socket.Connect(EndP);
}
catch
{
MessageBox.Show("Couldn't connect to the remote host " +
ip.ToString(), "Connection Error", MessageBoxButtons.OK,
MessageBoxIcon.Error);
}
connection_finished();
}

private void connection_finished()
{
if (this.InvokeRequired)
{
ConnFinishCallback d = new ConnFinishCallback(connection_finished);
Invoke(d, new object[] { });
}
else
{
if (FTP_Socket.Connected)
LStatus.Text = "Connected to " + ip.ToString();
else
LStatus.Text = "Disconnected";
}
}

Socket.Connect(EndPoint remoteEP) is a blocking method (I run it in another
Thread), if it can't make the connection it should take about 20 secs trying
to connect to the endpoint and if it can make the connection it did
inmediatly. If it doesn't connect, a message is shown, anyway I call the
connection_finished method that checks if FTP_Socket.Connected is true or
false to keep on with the main program. The problem is that as I use the
port 21 for the FTP Client, I always obtain the Socket.Connected true.

What is the problem with the port 21?

I've solved my problem cheking if I receive any response after the
connection, but I would like to know why the Socket doesn't try to connect
to any endpoint that uses the port 21 and puts the Socket.Connected var
always to true.

Regards,

Diego Escalona.

 

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

Do you know by any change if your network has a firewall?

It seems that you might have a FTP proxy server soemwhere in between.

 

[Diego Escalona]

Thanks for your answer,

I'm not sure if I have any FTP proxy server, so I unpuggled my network
cables and put only one of them connecting my machine with another one. The
result is the same as before, it always says it is connected with any IP
Address if I use the port 21, so I did a test with all my cables unplugged
using port 21 and then it couldn't connect, it seems it detects if I have my
network cables unplugged to make the connection, but the problem is still
there if I have any network cable connected..

Any other idea?

Regards,

Diego Escalona

Hi,

Do you know by any change if your network has a firewall?

It seems that you might have a FTP proxy server soemwhere in between.


--
Ignacio Machin
http://www.laceupsolutions.com
Mobile & warehouse Solutions.

Hello everybody,

I'm developing a FTP Client using the socket class. Here is the code I
use to declare the socket:

Socket FTP_Socket = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);

I've developed other applications (not with the port 21) with sockets and
to verify the connection I always use the Socket.Connected var. In this
case I noticed that there was a problem because the FTP_Socket always
connects (gets Connected var true) to the remote Endpoint. It doesn't
mind the IP Address, it always connects if the remote Endpoint uses the
port 21. In order to verify that, I've developed a little tool that makes
simple socket connections and I always obtain the same results, it
connects to any IP Address (they can be not real) if I use the port 21.

Here is the code I use to connect with my little tool:

private void connect()
{
try
{
FTP_Socket.Connect(EndP);
}
catch
{
MessageBox.Show("Couldn't connect to the remote host " +
ip.ToString(), "Connection Error", MessageBoxButtons.OK,
MessageBoxIcon.Error);
}
connection_finished();
}

private void connection_finished()
{
if (this.InvokeRequired)
{
ConnFinishCallback d = new
ConnFinishCallback(connection_finished);
Invoke(d, new object[] { });
}
else
{
if (FTP_Socket.Connected)
LStatus.Text = "Connected to " + ip.ToString();
else
LStatus.Text = "Disconnected";
}
}

Socket.Connect(EndPoint remoteEP) is a blocking method (I run it in
another Thread), if it can't make the connection it should take about 20
secs trying to connect to the endpoint and if it can make the connection
it did inmediatly. If it doesn't connect, a message is shown, anyway I
call the connection_finished method that checks if FTP_Socket.Connected
is true or false to keep on with the main program. The problem is that as
I use the port 21 for the FTP Client, I always obtain the
Socket.Connected true.

What is the problem with the port 21?

I've solved my problem cheking if I receive any response after the
connection, but I would like to know why the Socket doesn't try to
connect to any endpoint that uses the port 21 and puts the
Socket.Connected var always to true.

Regards,

Diego Escalona.