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Socket.Connect Method (String, Int32)

Establishes a connection to a remote host. The host is specified by a host name and a port number.

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

'Declaration
Public Sub Connect ( _
	host As String, _
	port As Integer _
)

Parameters

host
Type: System.String

The name of the remote host.

port
Type: System.Int32

The port number of the remote host.

ExceptionCondition
ArgumentNullException

host is Nothing.

ArgumentOutOfRangeException

The port number is not valid.

SocketException

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

ObjectDisposedException

The Socket has been closed.

NotSupportedException

This method is valid for sockets in the InterNetwork or InterNetworkV6 families.

InvalidOperationException

The Socket is Listening.

If you are using a connection-oriented protocol such as TCP, the Connect method synchronously establishes a network connection between LocalEndPoint and the specified remote host. If you are using a connectionless protocol, Connect establishes a default remote host. After you call Connect you can send data to the remote device with the Send method, or receive data from the remote device with the Receive method.

If you are using a connectionless protocol such as UDP, you do not have to call Connect before sending and receiving data. You can use SendTo and ReceiveFrom to synchronously communicate with a remote host. If you do call Connect any datagrams that arrive from an address other than the specified default will be discarded. If you want to set your default remote host to a broadcast address, you must first call the SetSocketOption method and set the socket option to SocketOptionName.Broadcast, or Connect will throw a SocketException. If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error.

Connect method will block, unless you specifically set the Blocking property to false prior to calling Connect. If you are using a connection-oriented protocol like TCP and you do disable blocking, Connect will throw a SocketException because it needs time to make the connection. Connectionless protocols will not throw an exception because they simply establish a default remote host. You can use SocketException.ErrorCode to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error. If the error returned WSAEWOULDBLOCK, the remote host connection has been initiated by a connection-oriented Socket, but has not yet completed successfully. Use the Poll method to determine when the Socket is finished connecting.

If IPv6 is enabled and the Connect(String, Int32) method is called to connect to a host that resolves to both IPv6 and IPv4 addresses, the connection to the IPv6 address will be attempted first before the IPv4 address. This may have the effect of delaying the time to establish the connection if the host is not listening on the IPv6 address.

NoteNote

If you are using a connection-oriented protocol and did not call Bind before calling Connect, the underlying service provider will assign the local network address and port number. If you are using a connectionless protocol, the service provider will not assign a local network address and port number until you complete a send or receive operation. If you want to change the default remote host, call Connect again with the desired endpoint.

NoteNote

If the socket has been previously disconnected, then you cannot use this method to restore the connection. Use one of the asynchronous BeginConnect methods to reconnect. This is a limitation of the underlying provider.

NoteNote

This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.

The following code example connects to a remote endpoint and then verifies the connection.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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