UDP connection packet

[Parisa_1]

Hello,

I am going to create an active lan devices application in VB.NET. Here is my code:

Imports System.Threading, System.Net.Sockets, System.Text, System.IO, System.Net

Public Class Form1
Dim th As Thread
Dim sock As UdpClient
Dim ip As String = "255.255.255.255"
Dim port As Integer = 1901
Dim Aux As String
Dim SearchVar() As Byte = {&HFF, &H1, &H1, &H2}

Private Sub search()
Dim IpEnd As IPEndPoint = New IPEndPoint(IPAddress.Any, 100)

Try
Do
Dim bytes() As Byte = sock.Receive(IpEnd)
Aux = Encoding.Default.GetString(bytes)
If Aux <> "" Then
Me.Invoke(New EventHandler(AddressOf add))
Aux = ""
End If

Loop
Catch ex As Exception

End Try

End Sub
Private Sub add()
ListBox1.Items.Add(Aux)
End Sub

Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
sock = New UdpClient
sock.Connect(ip, port)
sock.Send(SearchVar, SearchVar.Length)
th = New Thread(AddressOf Me.search)

th.Start()
End Sub


End Class

Here is output of my application which no device responses to me.



In contrast, A similar application has these results.



what is my mistake?

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