Set IP and DNS to use DHCP from WMI in VB.net

Question

I'm trying to interact with WMI through a vb.net program in order to make any machine that runs this program pull the IP settings and DNS server settings from DHCP for all network adapters with an IP.

The code I presently have works for DHCP without issue, but does not change DNS settings. The program compiles and executes without issue, but the DNS settings are not changing to be fetched automatically from DHCP.

    Dim objMC As ManagementClass = New ManagementClass("Win32_NetworkAdapterConfiguration")
    Dim objMOC As ManagementObjectCollection = objMC.GetInstances()

    For Each objMO As ManagementObject In objMOC
        If (Not CBool(objMO("IPEnabled"))) Then
            Continue For
        End If

        Try
            Dim objNewIP As ManagementBaseObject = Nothing
            Dim objSetIP As ManagementBaseObject = Nothing
            Dim objNewDNS As ManagementBaseObject = Nothing
            Dim objSetDNS As ManagementBaseObject = Nothing

            objNewIP = objMO.GetMethodParameters("EnableDHCP")
            objSetIP = objMO.InvokeMethod("EnableDHCP", Nothing, Nothing)
            objNewDNS = objMO.GetMethodParameters("SetDNSServerSearchOrder")
            objSetDNS = objMO.InvokeMethod("SetDNSServerSearchOrder", Nothing, Nothing)

        Catch ex As Exception
            MessageBox.Show("Settings unchanged : " & ex.Message)
        End Try
    Next objMO

I'm so close to getting this solved, I just need help to figure out this last step.

Answer 1

You annoyingly have to do it through the registry, they didn't add WMI methods for it. Specifically (taken from here: https://gallery.technet.microsoft.com/7b1cec46-bdb8-4afc-b240-9789eefce6de) you need to set this key to null.

"HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\" 

Below is your code with the necessary new sub inserted in

    Const conKeyPath = "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces"

    Public Sub Test()

    Dim objMC As ManagementClass = New ManagementClass("Win32_NetworkAdapterConfiguration")
    Dim objMOC As ManagementObjectCollection = objMC.GetInstances()

    For Each objMO As ManagementObject In objMOC
        If (Not CBool(objMO("IPEnabled"))) Then
            Continue For
        End If

        Try
            Dim objNewIP As ManagementBaseObject = Nothing
            Dim objSetIP As ManagementBaseObject = Nothing
            Dim objNewDNS As ManagementBaseObject = Nothing
            Dim objSetDNS As ManagementBaseObject = Nothing

            objNewIP = objMO.GetMethodParameters("EnableDHCP")
            objSetIP = objMO.InvokeMethod("EnableDHCP", Nothing, Nothing)
            objNewDNS = objMO.GetMethodParameters("SetDNSServerSearchOrder")
            objSetDNS = objMO.InvokeMethod("SetDNSServerSearchOrder", Nothing, Nothing)
            SetDNSAutomatically(objMO.GetPropertyValue("settingID"))

        Catch ex As Exception
            MessageBox.Show("Settings unchanged : " & ex.Message)
        End Try
    Next objMO
End Sub
Private Sub SetDNSAutomatically(ByVal settingID As String)
    If settingID = String.Empty Then
        Throw New ArgumentNullException("settingID")
    End If

     Dim _adapterKeyPath = String.Format("{0}\{1}", conKeyPath, settingID)
    My.Computer.Registry.SetValue(_adapterKeyPath, "NameServer", String.Empty)

End Sub