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Socket.Listen Method

Places a Socket in a listening state.

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

public void Listen(
	int backlog
)

Parameters

backlog
Type: System.Int32

The maximum length of the pending connections queue.

ExceptionCondition
SocketException

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

ObjectDisposedException

The Socket has been closed.

Listen causes a connection-oriented Socket to listen for incoming connection attempts. The backlog parameter specifies the number of incoming connections that can be queued for acceptance. To determine the maximum number of connections you can specify, retrieve the MaxConnections value. Listen does not block.

If you receive a SocketException, use the 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. Use Accept or BeginAccept to accept a connection from the queue.

NoteNote

You must call the Bind method before calling Listen, or Listen will throw a SocketException.

NoteNote

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

NoteNote

The backlog parameter is limited to different values depending on the Operating System. You may specify a higher value, but the backlog will be limited based on the Operating System.

The following code example uses Socket to listen for incoming connections.

        // create the socket
        Socket listenSocket = new Socket(AddressFamily.InterNetwork, 
                                         SocketType.Stream,
                                         ProtocolType.Tcp);

        // bind the listening socket to the port
	IPAddress hostIP = (Dns.Resolve(IPAddress.Any.ToString())).AddressList[0];
        IPEndPoint ep = new IPEndPoint(hostIP, port);
        listenSocket.Bind(ep); 

        // start listening
        listenSocket.Listen(backlog);

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, 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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