Quickest way to check if list of computers are online or not

Question

Hi

I have a list of computer names which i need to loop through and check to see which of them are online (accessible) before I then proceed with the next step in my app. In my powershell script which I am converting to a VB.net app I was using the below which worked quite quickly

Foreach ($ADcomputer in $ADcomputers) {  
      
    Write-Progress -Activity "Testing connection" -Status $ADcomputer -PercentComplete (($count / $ADcomputers.Count) * 100)  
  
    If (Test-Connection -ComputerName $ADcomputer -Quiet -Count 1 -ErrorAction SilentlyContinue) {  
        $online += $ADcomputer  
    }  
    Else {  
        $offline += $computer  
    }  
      
    $count += 1  
  
}  

In VB I have tried using the below but it is quite a lot slower

Dim online As New List(Of String)  
        Dim offline As New List(Of String)  
        For Each r In result  
  
            Try  
                If My.Computer.Network.Ping(r.ToString, 1) Then  
                    online.Add(r.ToString)  
                Else  
                    offline.Add(r.ToString)  
                End If  
            Catch ex As Exception  
                offline.Add(r.ToString)  
            End Try  
        Next  

So hence my question what would be the best way to quckly check if a computer is online, these are all domain connected computers, so on reliable quick connections usually, and the list of computers I would be checking is usually around 400 computers.

Answer 1

You could run Start-Job and collect the results of the checks etc with X number of cores at the same time. That would make your checks exponentially faster.

Answer 2

Another method that you can test is by calling IcmpSendEcho directly.

Cannot post test code here (bug in those forums...) : IcmpSendEcho test in VB
(probably you should reduce the TimeOut, maybe to a few ms)

Declarations :

<DllImport("Iphlpapi.dll", SetLastError:=True, CharSet:=CharSet.Auto)>  
Public Shared Function IcmpSendEcho(IcmpHandle As IntPtr, DestinationAddress As Integer, RequestData As String,  
      RequestSize As Short, RequestOptions As IntPtr, ByRef ReplyBuffer As ICMP_ECHO_REPLY, ReplySize As UInteger, Timeout As UInteger) As UInteger  
End Function  
  
<DllImport("Iphlpapi.dll", SetLastError:=True, CharSet:=CharSet.Auto)>  
Public Shared Function IcmpCreateFile() As IntPtr  
End Function  

<DllImport("Iphlpapi.dll", SetLastError:=True, CharSet:=CharSet.Auto)>  
Public Shared Function IcmpCloseHandle(IcmpHandle As IntPtr) As Boolean  
End Function  
  
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>  
Public Structure ICMP_ECHO_REPLY  
    Public Address As Integer  
    Public Status As UInteger  
    Public RoundTripTime As UInteger  
    Public DataSize As UShort  
    Public Reserved As UShort  
    Public Data As IntPtr  
    Public Options As ICMP_OPTIONS  
End Structure  

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>  
Public Structure ICMP_OPTIONS  
    Public Ttl As Byte  
    Public Tos As Byte  
    Public Flags As Byte  
    Public OptionsSize As Byte  
    Public OptionsData As IntPtr  
End Structure  

Answer 3

Test-Connection calls WMI with Win32_PingStatus, so you can do the same thing in VB, with request like :

(remove space in Selec t...)
"Selec t * from Win32_PingStatus where ((Address='COMPUTERNAME') And TimeToLive=80 And BufferSize=32)"