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TcpClient.BeginConnect Method (IPAddress, Int32, AsyncCallback, Object)

Begins an asynchronous request for a remote host connection. The remote host is specified by an IPAddress and a port number (Int32).

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

public IAsyncResult BeginConnect (
	IPAddress address,
	int port,
	AsyncCallback requestCallback,
	Object state
public IAsyncResult BeginConnect (
	IPAddress address, 
	int port, 
	AsyncCallback requestCallback, 
	Object state
public function BeginConnect (
	address : IPAddress, 
	port : int, 
	requestCallback : AsyncCallback, 
	state : Object
) : IAsyncResult
Not applicable.



The IPAddress of the remote host.


The port number of the remote host.


An AsyncCallback delegate that references the method to invoke when the operation is complete.


A user-defined object that contains information about the connect operation. This object is passed to the requestCallback delegate when the operation is complete.

Return Value

An IAsyncResult object that references the asynchronous connection.

Exception typeCondition


The address parameter is a null reference (Nothing in Visual Basic).


An error occurred when attempting to access the socket. See the Remarks section for more information.


The Socket has been closed.


A caller higher in the call stack does not have permission for the requested operation.


The port number is not valid.

The asynchronous BeginConnect operation must be completed by calling the EndConnect method. Typically, the method is invoked by the asyncCallback delegate.

This method does not block until the operation completes. To block until the operation completes, use one of the Connect method overloads.

For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.

The following code example creates a TcpClient and connects to a remote host.

        public static void DoBeginConnect1(string host, int port)
            // Connect asynchronously to the specifed host.
            TcpClient t = new TcpClient(AddressFamily.InterNetwork);
//            IPAddress remoteHost = new IPAddress(host);
            IPAddress[] remoteHost = Dns.GetHostAddresses(host);


            Console.WriteLine("Establishing Connection to {0}", 
            t.BeginConnect(remoteHost[0], port, 
                new AsyncCallback(ConnectCallback), t);

            // Wait here until the callback processes the connection.

            Console.WriteLine("Connection established");

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