Ping subnet

  • Thread starter Thread starter Ryan
  • Start date Start date
R

Ryan

I want to ping every IP on a subnet (255 IP's) and display in a table what
IP's are active. I'm currently using a For loop but this takes forever
because it pauses to test each Ping. So my guess is that I need to run 255
functions each in their own thread. Would there be an easy way to do this,
maybe create the functions dynamically within a loop? Any help with the
syntax would be great. I haven't done much threaded programming.
 
Do you need this functionality as part of an existing app or are you trying to
write something that does this? There are already apps out there that do this
very quickly, like nmap.
 
Hi Ryan,

For such scenario, I recommend use several BackgroundWorker instances to do
the ping and update UI to report IP address's status.

First, we need to create a class to provide the next IP address that needs
to ping:

Public Class IpProvider
Private _index As Integer = 0
Public ReadOnly Property GetNextIpAddress() As String
Get
SyncLock GetType(IpProvider)
If _index = 255 Then Return Nothing
_index = _index + 1
Return "192.168.1." + _index.ToString()
End SyncLock
End Get
End Property
End Class

Here I'm using a hardcoded subnet for demostrating purpose. You may need to
use some properties to set the specified subnet.

Add a ListBox to your Form which will display each IP address's status. Add
two buttons, the first one will be used to start the ping threads, the
second one will be used to cancel the ping threads. Here we will use 5
threads to do the ping, each thread will use the IpProvider to get the next
ip address to ping.

Const THREAD_COUNT As Integer = 5
Private bws(THREAD_COUNT - 1) As BackgroundWorker

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim ipp As New IpProvider

For i As Integer = 0 To THREAD_COUNT - 1
Dim bw As New BackgroundWorker
bw.WorkerReportsProgress = True
bw.WorkerSupportsCancellation = True

AddHandler bw.DoWork, AddressOf bw_DoWork
AddHandler bw.ProgressChanged, AddressOf bw_ProgressChanged
AddHandler bw.RunWorkerCompleted, AddressOf
bw_RunWorkerCompleted
bw.RunWorkerAsync(ipp)

bws(i) = bw
Next
End Sub

Private Sub bw_DoWork(ByVal sender As Object, ByVal e As
DoWorkEventArgs)
Dim bw As BackgroundWorker = CType(sender, BackgroundWorker)
e.Result = PingIp(e.Argument, bw, e)
End Sub

Private Sub bw_ProgressChanged(ByVal sender As Object, ByVal e As
ProgressChangedEventArgs)
ListBox1.Items.Add(e.UserState)
End Sub

Private Sub bw_RunWorkerCompleted(ByVal sender As Object, ByVal e As
RunWorkerCompletedEventArgs)
If (e.Error IsNot Nothing) Then
ListBox1.Items.Add(e.Error.Message)
ElseIf e.Cancelled Then

Else

End If
End Sub

Private Function PingIp(ByVal ipp As IpProvider, ByVal bw As
BackgroundWorker, ByVal e As DoWorkEventArgs) As Boolean
While True
If bw.CancellationPending Then
e.Cancel = True
Return False
Else
Dim ipaddress = ipp.GetNextIpAddress()
If ipaddress Is Nothing Then Exit While
' insert code to ping the address, here we're using Sleep()
to simulate a delay
Thread.Sleep(1000)

' then we report the result, here we don't care the
progress percentage
bw.ReportProgress(0, ipaddress + " is alive")
End If
End While
Return True
End Function

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button2.Click
For i As Integer = 0 To THREAD_COUNT - 1
bws(i).CancelAsync()
Next
End Sub

Hope this helps. Please feel free to post here if anything is unclear.

Sincerely,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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