Правильно пропинговать кучку IP

 For i As Integer = 0 To DataGridView1.RowCount - 1
 
            Dim IP As String = DataGridView1.Item(2, i).Value
 
            If My.Computer.Network.Ping(IP, 2) Then
                DataGridView1.Rows(i).Cells(0).Value = New Bitmap("C:\box_green.png")
            Else
                DataGridView1.Rows(i).Cells(0).Value = New Bitmap("C:\box_red.png")
            End If
 
        Next

Private Sub Button1_Click
Call Module1.Main()

Imports System.Threading
Public Class Form1
    Public Shared t As Date
 
    Public Shared a As New Hashtable
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        t = Now
        For i = 0 To 255
 
            Dim Thread6 As Thread
            Dim oWorker6 As New WorkerThreadClass()
            Thread6 = New Thread(AddressOf _
          oWorker6.WorkerThread)
            'передаем исходные данные:
            oWorker6.Start = i
            oWorker6.Finish = i
 
            Thread6.Start()
        Next
 
    End Sub
    Public Class WorkerThreadClass
        Public Start As Integer
        Public Finish As Integer
        Public Sub WorkerThread()
            For i = Start To Finish
 
                If My.Computer.Network.Ping("192.168.0." & i) Then
                    'MsgBox("онлайн 192.168.0." & i)
                    a("192.168.0." & i) = True
                Else
                    a("192.168.0." & i) = False
                End If
       
 
                If i = 255 Then
                    System.Threading.Thread.Sleep(3000)
                    For ix = 0 To 255
 
                        Dim Thread6 As Thread
                        Dim oWorker6 As New WorkerThreadClass()
                        Thread6 = New Thread(AddressOf _
                      oWorker6.WorkerThread)
                        'передаем исходные данные:
                        oWorker6.Start = ix
                        oWorker6.Finish = ix
                        Thread6.Start()
                    Next
                End If
 
            Next
        End Sub
    End Class
    Dim x As Integer
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        ListView1.Clear()
        x = a.Count
        If x <> 256 Then Exit Sub
        For Each str3 As System.Collections.DictionaryEntry In a
            Application.DoEvents()
            If str3.Value = True Then
                ListView1.Items.Add(str3.Key)
            End If
        Next
    End Sub
End Class

 For i = 1 To 2
     ..................
        Next

 Sub Main()
        ' описание первого процесса
        Dim Thread1 As Thread
        Dim oWorker1 As New WorkerThreadClass()
        Thread1 = New Thread(AddressOf _
          oWorker1.WorkerThread)
        ' Thread1.Priority = _
        '  ThreadPriority.BelowNormal  
        ' передаем исходные данные:
        oWorker1.Start = 101
 
        ' описание второго процесса
        Dim Thread2 As Thread
        Dim oWorker2 As New WorkerThreadClass()
        Thread2 = New Thread(AddressOf _
           oWorker2.WorkerThread)
        ' передаем исходные данные:
        oWorker2.Start = 102
 
        Thread1.Start()
        Thread2.Start()
 
        Thread1.Join()
        Thread2.Join()
    End Sub

Dim Thread As Thread
 
For i = 1 To 2
        Dim oWorker &i As New WorkerThreadClass()
        Thread&i = New Thread(AddressOf _
          oWorker&i.WorkerThread)
          oWorker&i.Start = 101
          Thread&i.Start()
          Thread&i.Join()
Next

 For i = 1 To 2
 
            Dim Thread(i) As Thread
            Dim oWorker(i) As New WorkerThreadClass()
            Thread(i) = New Thread(AddressOf _
              oWorker(i).WorkerThread)
            oWorker(i).Start = 101
 
        Next