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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 array and a port number (Int32).

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

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


Type: System.Net.IPAddress[]

At least one IPAddress that designates the remote hosts.

Type: System.Int32

The port number of the remote hosts.

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 addresses 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 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 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.

This method is typically used immediately after a call to the BeginGetHostAddresses method, which can return multiple IP addresses for a single host.

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

// Connect asynchronously to the specifed host. 
public static void DoBeginConnect2(string host, int port)
    TcpClient t = new TcpClient(AddressFamily.InterNetwork);
    IPAddress[] remoteHost = Dns.GetHostAddresses(host);


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

    // Wait here until the callback processes the connection.

    Console.WriteLine("Connection established");
// Connect asynchronously to the specifed host.
static void DoBeginConnect2(String* host, int port)
    TcpClient* t = new TcpClient(AddressFamily::InterNetwork);
    IPAddress* remoteHost[] = Dns::ResolveToAddresses(host);


    Console::WriteLine(S"Establishing Connection to {0}", host);
    t->BeginConnect(remoteHost, port, 
        new AsyncCallback(&ConnectCallback), t);

    // Wait here until the callback processes the connection.

    Console::WriteLine(S"Connection established");

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

Supported in: 3.5, 3.0, 2.0