TcpListener Class

TcpListener Class

Listens for connections from TCP network clients.

Namespace: System.Net.Sockets
Assembly: System (in system.dll)

Public Class TcpListener
Dim instance As TcpListener

public class TcpListener
public class TcpListener
Not applicable.

The TcpListener class provides simple methods that listen for and accept incoming connection requests in blocking synchronous mode. You can use either a TcpClient or a Socket to connect with a TcpListener. Create a TcpListener using an IPEndPoint, a Local IP address and port number, or just a port number. Specify Any for the local IP address and 0 for the local port number if you want the underlying service provider to assign those values for you. If you choose to do this, you can use the LocalEndpoint property to identify the assigned information, after the socket has connected.

Use the Start method to begin listening for incoming connection requests. Start will queue incoming connections until you either call the Stop method or it has queued MaxConnections. Use either AcceptSocket or AcceptTcpClient to pull a connection from the incoming connection request queue. These two methods will block. If you want to avoid blocking, you can use the Pending method first to determine if connection requests are available in the queue.

Call the Stop method to close the TcpListener.


The Stop method does not close any accepted connections. You are responsible for closing these separately.

The following code example creates a TcpListener.

Imports System
Imports System.IO
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports Microsoft.VisualBasic

Class MyTcpListener

    Public Shared Sub Main()

	Dim server As TcpListener
            ' Set the TcpListener on port 13000.
         Dim port As Int32 = 13000
         Dim localAddr As IPAddress = IPAddress.Parse("")

         server = New TcpListener(localAddr, port)
         ' Start listening for client requests.
         ' Buffer for reading data
            Dim bytes(1024) As Byte
            Dim data As String = Nothing
         ' Enter the listening loop.
         While True
            Console.Write("Waiting for a connection... ")
            ' Perform a blocking call to accept requests.
            ' You could also user server.AcceptSocket() here.
            Dim client As TcpClient = server.AcceptTcpClient()
            data = Nothing
            ' Get a stream object for reading and writing
            Dim stream As NetworkStream = client.GetStream()
            Dim i As Int32
            ' Loop to receive all the data sent by the client.
            i = stream.Read(bytes, 0, bytes.Length)
            While (i <> 0) 
               ' Translate data bytes to a ASCII string.
               data = System.Text.Encoding.ASCII.GetString(bytes, 0, i)
                    Console.WriteLine("Received: {0}", data)
               ' Process the data sent by the client.
               data = data.ToUpper()
                    Dim msg As Byte() = System.Text.Encoding.ASCII.GetBytes(data)
               ' Send back a response.
               stream.Write(msg, 0, msg.Length)
                    Console.WriteLine("Sent: {0}", data)
               i = stream.Read(bytes, 0, bytes.Length)

            End While
            ' Shutdown and end connection
         End While
      Catch e As SocketException
         Console.WriteLine("SocketException: {0}", e)
      End Try
      Console.WriteLine(ControlChars.Cr + "Hit enter to continue....")
   End Sub 'Main

End Class 'MyTcpListener 

See TcpClient for a client example.

  • SocketPermission  to establish an outgoing connection or accept an incoming request.


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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