Question

No connection could be made because the target machine actively refused it

Asked by: John500

I'm trying to create a bare-bones socket application.  I'm using the following code from MSDN to see how the connection is made etc, etc.  Using the code from the snippet below, I get the following error:

No connection could be made because the target machine actively refused it  

The error appears on the line with asteriks.  Although I'm connected to a LAN and the Internet, I'm assuming this is all being attempted on my own machine.  The IP and port provided by the error message is indeed my machine.

Thanks!

Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Text
 
 
' State object for receiving data from remote device.
 
Public Class StateObject
    ' Client socket.
    Public workSocket As Socket = Nothing
    ' Size of receive buffer.
    Public Const BufferSize As Integer = 256
    ' Receive buffer.
    Public buffer(BufferSize) As Byte
    ' Received data string.
    Public sb As New StringBuilder
End Class 'StateObject
 
 
Public Class AsynchronousClient
    ' The port number for the remote device.
    Private Const port As Integer = 11000
 
    ' ManualResetEvent instances signal completion.
    Private Shared connectDone As New ManualResetEvent(False)
    Private Shared sendDone As New ManualResetEvent(False)
    Private Shared receiveDone As New ManualResetEvent(False)
 
    ' The response from the remote device.
    Private Shared response As String = String.Empty
 
 
    Public Shared Sub Main()
        ' Establish the remote endpoint for the socket.
        ' For this example use local machine.
        Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName())
        Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
        Dim remoteEP As New IPEndPoint(ipAddress, port)
 
        ' Create a TCP/IP socket.
        Dim client As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
 
        ' Connect to the remote endpoint.
        client.BeginConnect(remoteEP, New AsyncCallback(AddressOf ConnectCallback), client)
 
        ' Wait for connect.
        connectDone.WaitOne()
 
        ' Send test data to the remote device.
        Send(client, "This is a test<EOF>")
        sendDone.WaitOne()
 
        ' Receive the response from the remote device.
        Receive(client)
        receiveDone.WaitOne()
 
        ' Write the response to the console.
        Console.WriteLine("Response received : {0}", response)
 
        ' Release the socket.
        client.Shutdown(SocketShutdown.Both)
        client.Close()
    End Sub 'Main
 
 
    Private Shared Sub ConnectCallback(ByVal ar As IAsyncResult)
        ' Retrieve the socket from the state object.
        Dim client As Socket = CType(ar.AsyncState, Socket)
 
        ' Complete the connection.
        client.EndConnect(ar)            ****************************  ERROR HERE  ****************************
 
        Console.WriteLine("Socket connected to {0}", client.RemoteEndPoint.ToString())
 
        ' Signal that the connection has been made.
        connectDone.Set()
    End Sub 'ConnectCallback
 
 
    Private Shared Sub Receive(ByVal client As Socket)
 
        ' Create the state object.
        Dim state As New StateObject
        state.workSocket = client
 
        ' Begin receiving the data from the remote device.
        client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, New AsyncCallback(AddressOf ReceiveCallback), state)
    End Sub 'Receive
 
 
    Private Shared Sub ReceiveCallback(ByVal ar As IAsyncResult)
 
        ' Retrieve the state object and the client socket 
        ' from the asynchronous state object.
        Dim state As StateObject = CType(ar.AsyncState, StateObject)
        Dim client As Socket = state.workSocket
 
        ' Read data from the remote device.
        Dim bytesRead As Integer = client.EndReceive(ar)
 
        If bytesRead > 0 Then
            ' There might be more data, so store the data received so far.
            state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead))
 
            ' Get the rest of the data.
            client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, New AsyncCallback(AddressOf ReceiveCallback), state)
        Else
            ' All the data has arrived; put it in response.
            If state.sb.Length > 1 Then
                response = state.sb.ToString()
            End If
            ' Signal that all bytes have been received.
            receiveDone.Set()
        End If
    End Sub 'ReceiveCallback
 
 
    Private Shared Sub Send(ByVal client As Socket, ByVal data As String)
        ' Convert the string data to byte data using ASCII encoding.
        Dim byteData As Byte() = Encoding.ASCII.GetBytes(data)
 
        ' Begin sending the data to the remote device.
        client.BeginSend(byteData, 0, byteData.Length, 0, New AsyncCallback(AddressOf SendCallback), client)
    End Sub 'Send
 
 
    Private Shared Sub SendCallback(ByVal ar As IAsyncResult)
        ' Retrieve the socket from the state object.
        Dim client As Socket = CType(ar.AsyncState, Socket)
 
        ' Complete sending the data to the remote device.
        Dim bytesSent As Integer = client.EndSend(ar)
        Console.WriteLine("Sent {0} bytes to server.", bytesSent)
 
        ' Signal that all bytes have been sent.
        sendDone.Set()
    End Sub 'SendCallback
End Class 'AsynchronousClient
                                  
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Asked On
2009-09-03 at 11:52:37ID24705638
Tags

VB .NET

,

Sockets

Topics

Winsock

,

Signal Processing

,

Microsoft Visual Basic.Net

Participating Experts
1
Points
500
Comments
19

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Answers

 

by: ladarlingPosted on 2009-09-03 at 12:35:15ID: 25254145

You probably need to unblock port 11000 in the windows firewall. Failing that, you may need to install a loopback adapter.

http://support.microsoft.com/kb/839013

 

by: John500Posted on 2009-09-03 at 13:09:33ID: 25254427

Appreciate this info.

How would this loopback adapter be done?

 

by: ladarlingPosted on 2009-09-03 at 13:23:43ID: 25254571

What OS are you using?

 

by: John500Posted on 2009-09-03 at 13:34:21ID: 25254670

I'm using XP and I went through the Add Hardware wizard and installed the loopback adapter.  Then I rebooted but got the same thing.

Tell me, when these lines are executed:

      Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
        Dim remoteEP As New IPEndPoint(ipAddress, port)

What's going on with the IPEndPoint?  This is where I should establish the endpoint - right?  Should I hardcode my own IP ?

Also, you can see by the picture below that my new 2nd network connection isn't looking good.

Thanks!

 

by: John500Posted on 2009-09-03 at 13:40:37ID: 25254723

Also, when I look at the 'ipAddress' variable from this line:

 Dim remoteEP As New IPEndPoint(ipAddress, port)

It shows the message below for the loopback object

 

by: ladarlingPosted on 2009-09-03 at 13:45:05ID: 25254759

Yeah, you can, and you have to do it with a byte array. The loopback address is 127.0.0.1, so:

Dim localHost() As Byte = {127, 0, 0, 1}
Dim ipAddress As New IPAddress(localHost)

 

by: ladarlingPosted on 2009-09-03 at 13:46:32ID: 25254766

You most likely need an IPv4 address...

 

by: John500Posted on 2009-09-03 at 13:53:51ID: 25254829

>> You most likely need an IPv4 address...

Can you tell me how is would be accomplished?  

Also, do you think I need to get rid of the Dynamic IP assignment and hard code my IP or the loop back IP?

Thanks

 

by: ladarlingPosted on 2009-09-03 at 14:26:02ID: 25255124

The IPv4 loopback address for *all* network adapters is 127.0.0.1

This address refers to your machine even if you have a DHCP address assigned to it, or whatever.

 

by: ladarlingPosted on 2009-09-03 at 14:28:56ID: 25255145

So, to put it another way, any computer that you sit down at can be though of as 127.0.0.1

Or, every computer thinks that it is 127.0.0.1

 

by: John500Posted on 2009-09-04 at 05:08:58ID: 25258685

>>  So, to put it another way, any computer that you sit down at can be though of as 127.0.0.1

Ok, I'm with you on that.  

Since I enabled the loopback hardware, my computer now has two network cards per say.  This new, second network adapter has received a new IP address through DHCP but apparently it is only partially configured.  That is, it does not have a default gateway.  Also, my primary adapter starts with '192'...  but the loop back virtual network card shows a number starting with '169'...  

I see this using the IPCONFIG command and the adapter is identified by the words 'Connection 2'.   I would think the IPCONFIG command would have shown an address of 127.0.0.1 - what's up with that?  This is supposed to be the loopback network card and it shows something other than 127.0.0.1  

I tried to hard code the 127.0.0.1 in the IP properties but it wouldn't allow me saying, " this IP is reserved for loopback purposes only.  Pick another number starting with ..."

Thus, there must be some other step of configuration I'm leaving out - yes/no?

Thanks!

 

by: ladarlingPosted on 2009-09-04 at 06:05:13ID: 25259157

Yeah, you can completely uninstall the loopback adapter if 127.0.0.1 works in your code.

Go to the command prompt an ping 127.0.0.1, it will already be live... You can also use 'localhost', which resolves internally in the system to 127.0.0.1

The loopback adapter is a hardware representation of a loopback which allows you to configure some other IP address as the address, but it is in addition to localhost.

 

by: John500Posted on 2009-09-04 at 06:51:04ID: 25259642

>> uninstall the loopback adapter if 127.0.0.1 works in your code.

No, I haven't got anything to work yet.

>> Go to the command prompt an ping 127.0.0.1

Yes, I get a reply but something still isn't right if I consider the 2nd adapter's icon in the tray (see the picture)

>> You can also use 'localhost', which resolves internally in the system to 127.0.0.1

To put it yet another way, the call to
          Dns.GetHostEntry(Dns.GetHostName())

... is supposed to also obtain the local host IP - right?  But for some reason, the attempt to obtain an end-point of my local address is failing.  Look again at these lines of code from the snippet in my first post:

 ' Establish the remote endpoint for the socket.
 ' For this example use local machine.
        Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName())
        Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
        Dim remoteEP As New IPEndPoint(ipAddress, port)

Yet when the code hits this line:

        ' Complete the connection.
        client.EndConnect(ar)            ****************************  ERROR HERE  ****************************

It doesn't like the value of 'ar'  --  and gives the following error:

No connection could be made because the target machine actively refused it IP # 192....  : 11000

As we talked about earlier, I made an exception for this port in the firewall but still the same thing.

Any ideas??  Thanks!


         


Private Shared Sub ConnectCallback(ByVal ar As IAsyncResult)
        ' Retrieve the socket from the state object.
        Dim client As Socket = CType(ar.AsyncState, Socket)
        Try
            ' Complete the connection.
            client.EndConnect(ar)        *********************** ERROR HERE *************************
            Console.WriteLine("Socket connected to {0}", client.RemoteEndPoint.ToString())
 
            ' Signal that the connection has been made.
            connectDone.Set()
        Catch ex As Exception
 
        End Try
 
    End Sub 'ConnectCallback

                                              
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by: ladarlingPosted on 2009-09-04 at 06:59:05ID: 25259718

Forget about the loopback adapter for a moment... :-), It is *not* necessary if you can use the machines internal loopback IP address... Have you tried?

' Establish the remote endpoint for the socket.
' For this example use local machine.
  Dim localHost() As Byte = {127, 0, 0, 1}
   Dim ipAddress As New IPAddress(localHost)
  Dim remoteEP As New IPEndPoint(ipAddress, port)

 

by: John500Posted on 2009-09-04 at 07:40:31ID: 25260142

>> Forget about the loopback adapter for a moment

Surely.  I disabled that adapter so my machine would certainly now be using the one true adapter.

I ran the program with the code you provided.  However, I got the same error except it now read like this:

                    No connection could be made because the target machine actively refused it IP # 127.0.0.1 : 11000

What do you think?

 

by: ladarlingPosted on 2009-09-04 at 08:22:47ID: 25260521

Hmmmm. Try to connect to your port via telnet from the command prompt:

telnet localhost 11000

And see what you get.

 

by: John500Posted on 2009-09-04 at 08:46:04ID: 25260731

Ok, here's what I have:

C:\>telnet localhost 11000
Connecting To localhost...Could not open connection to the host, on port 11000:
Connect failed

Could this be due to 'Trend Micro' ?  As I say, I already have an exception set up for the Windows Firewall..........

 

by: ladarlingPosted on 2009-09-04 at 08:52:47ID: 25260812

It very well could be... A lot of antivirus products block unknown port activity.

 

by: John500Posted on 2009-09-04 at 11:45:00ID: 25262248

Looks like I'm forced to use an offline computer on this one.  I can't fool with these Trend Micro settings.

Thanks a lot for you help on this!  If you get bored, I have another one dealing with sockets that isn't getting any action.

http://www.experts-exchange.com/Programming/Languages/Winsock/Q_24704379.html

The code is all right there from a sample project, I was looking for some help interpreting it.

John

20120131-EE-VQP-002

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