I just made a simple TCP server to experiment socket exception when I lost
the connection with my client.
In this test program I create a socket and wait for a client (a basic telnet
on another computer of my LAN) to connect. When the client is well connected,
I unplug the ethernet wire of the client and I wait for exception.
I thought that I will have an exception the next time I try to use the
socket to send or receive data. So I try to send data to the disconnected
client and the send call directly return to me that all bytes have been sent
!!!
Moreover, I check after the socket.Connected Boolean and it's True.
I find some clues on this article :
http://dam.mellis.org/2004/08/net_socket_bugs_gotchas/

This is my server code :

Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text

Public Class Form1
   Dim port As Integer = 10000

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
       Dim sckListening As Socket
       Dim sckClient As Socket

       sckListening = New Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp)
       sckListening.Bind(New IPEndPoint(IPAddress.Any, port))
       sckListening.Listen(5)
       System.Console.WriteLine("Socket en écoute sur " &
sckListening.LocalEndPoint.ToString)
       sckClient = sckListening.Accept()
       System.Console.WriteLine("Serveur: Connexion acceptée avec " &
sckClient.RemoteEndPoint.ToString)

      'I try tu use the SendTimeout param
       sckClient.SendTimeout = 1000

      'Here we sleep during 50 sec
      'Between each sleep we check the socket.Connected var
       Dim i As Integer
       For i = 0 To 9
           System.Console.WriteLine("Attente de plantage ... " & CStr((i +
1) * 5) & "sec")
           System.Console.WriteLine("Socket connecté ? " &
sckClient.Connected.ToString)
           Threading.Thread.Sleep(5000)
       Next

      'Here we try to send 6 bytes to the disconnected client
       Dim nbByte As Integer
       nbByte = sckClient.Send(Encoding.ASCII.GetBytes("hello!"), 6,
SocketFlags.None)
       System.Console.WriteLine(CStr(nbByte))
 
      'You don't have any exception yet
      'I wait for exceptions maybe thrown due to the socket.sendtimeout
parameter
       For i = 0 To 9
           System.Console.WriteLine("Attente de plantage ... " & CStr((i +
1) * 5) & "sec")
           System.Console.WriteLine("Socket connecté ? " &
sckClient.Connected.ToString)
           Threading.Thread.Sleep(5000)
       Next

      'We finally made a success data send to a disconnected client without
any exception !!
       System.Console.WriteLine("Fin")
   End Sub
End Class

I search solutions to be able to detect client disconnection... Because the
.NET Framework appears to have some bugs in socket managing.

Thank You