Q194938: HOWTO: Monitor TCP/IP Ports in Use

Article: Q194938
Product(s): Microsoft Visual Basic for Windows
Version(s): 5.0,6.0
Operating System(s): 
Keyword(s): kbcode kbCtrl kbVBp kbVBp500 kbVBp600 kbGrpDSVB kbDSupport kbCodeSam
Last Modified: 24-JUL-2001

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The information in this article applies to:

- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SUMMARY
=======

This article describes how to monitor whether a TCP/IP port is in use.

MORE INFORMATION
================

There are times when it is necessary to know or monitor whether a port is in
use. The following sample demonstrates how this is done.

1. Create a new Standard EXE project. Form1 is created by default.

2. Add 1 Timer, 2 Labels, 1 Listbox, 1 TextBox and 2 CommandButton controls to
  Form1. Position Label1 above Text1 and Label2 above List1.

3. Set the Sorted property of List1 to True.

4. Add the following code to the General Declarations section of Form1:

        Option Explicit

        Const PortsChecked = 200

        Private Sub Command1_Click()
           Timer1.Enabled = True
           Timer1.Interval = 1000
        End Sub

        Private Sub Command2_Click()
           Timer1.Interval = 0
           Timer1.Enabled = False
        End Sub

        Private Sub Timer1_Timer()
           Dim X As Integer

           List1.Clear
           For X = 1 To PortsChecked
              DoEvents
              Text1.Text = X
              WinSock1.LocalPort = X
              On Error Resume Next
              WinSock1.Listen  ' If we get an error, the port is busy.
              If Err.Number = 10048 Then
                 List1.AddItem X  ' Log Active port # to list box.
                 Err.Number = 0
              End If

              WinSock1.Close
           Next X
        End Sub

        Private Sub Form_Load()
           Label1.Caption = "Checking Port #"
           Label2.Caption = "Ports In Use"
           Command1.Caption = "Start"
           Command2.Caption = "End"
           Text1.Locked = True
        End Sub

5. Run the program. If, for example, you have an active DCOM connection, you
  should see 135 displayed in the ListBox.

  To change the number of ports checked, modify the constant PortsChecked. To
  change the amount of time between samples modify the constant TimerInt.

REFERENCES
==========

For additional information, please see the following article in the Microsoft
Knowledge Base:

  Q173619 PRB: Winsock Control Generates Error 10048 - Address in Use

Also search Visual Basic Help for "Using the Winsock Control."

(c) Microsoft Corporation 1998, All Rights Reserved.
Contributions by Richard T. Edwards, Microsoft Corporation


Additional query words:

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Keywords          : kbcode kbCtrl kbVBp kbVBp500 kbVBp600 kbGrpDSVB kbDSupport kbCodeSam 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVB500 kbVB600
Version           : :5.0,6.0
Issue type        : kbhowto

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