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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)

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public IAsyncResult BeginConnect(
	IPAddress address,
	int port,
	AsyncCallback requestCallback,
	Object state


Type: System.Net.IPAddress
The IPAddress of the remote host.
Type: System.Int32
The port number of the remote host.
Type: System.AsyncCallback
An AsyncCallback delegate that references the method to invoke when the operation is complete.
Type: System.Object
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

Type: System.IAsyncResult
An IAsyncResult object that references the asynchronous connection.


The address parameter is null.


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 HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

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");

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.