Managing netbootGuid

The attribute on AD computer objects netbootGuid is very important to allowing some deployment options (RIS and WDS) to locate the computer object the hardware belongs to.  Unfortunately certain activities, such as replacing the system board or swapping in new hardware but using a pre-existing computer name, can invalidate the accuracy of the netbootGuid attribute stored in AD.

I wrote the script below (more precisely cobbled together since my VBScript is very rusty) to automatically check to make sure the netbootGuid is correct and update it if it isn't.  This script can be deployed as a startup script via Group Policies to ensure every time the computer boots, the netbootGuid will be updated if needed.  However, in order for this to work, the ACLs on the computer objects must be changed to allow SELF to write to the netbootGuid property.

 References (from whence I cobbled):

• How to prestage an RIS client computer by using ADSI
• Working with Binary Data (GUIDs) in VBScript
• Eric Lippert's Blog

Note:  I'm not entirely fond of having to write out to a temp file to turn the GUID into a byte array.  But it works.  I'm open to feedback on alternate methods as to how I can rewrite the function baConvertGuidToByteArray without writing out to the temporary file.  Thanks in advance.

<VBScript>

'http://support.microsoft.com/kb/302467
'The sample uses WMI to return the UUID on the system.
'If a UUID can not be found on the system it returns all F's.
'What RIS does in this case is it uses a zero'd out version of the MAC
'address of the NIC the machine is booting off of.
'This sample will return the value required to set the
'netbootGUID attribute

Option Explicit

Call UpdateNetbootGuid(guidGetUUID, szGetDn)

Function guidGetUUID
 Dim SystemSet, SystemItem, NetworkAdapterSet, NetworkAdapter

 Set SystemSet = GetObject("winmgmts:").InstancesOf ("Win32_ComputerSystemProduct")
 For Each SystemItem In SystemSet
  If SystemItem.UUID = "FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF" Then
   Set NetworkAdapterSet = GetObject("winmgmts:").InstancesOf ("Win32_NetworkAdapter")
    For Each NetworkAdapter In NetworkAdapterSet
    If NetworkAdapter.AdapterType = "Ethernet 802.3" And NetworkAdapter.Description <> "Packet Scheduler Miniport" Then
     guidGetUUID = "00000000-0000-0000-0000-" & Replace(NetworkAdapter.MACAddress, ":", "")
    End If
   Next
  Else
   guidGetUUID = SystemItem.UUID
  End If   
 Next
End Function

Function szGetDN
' Use the NameTranslate object to convert the NT name of the computer to
' the Distinguished name required for the LDAP provider. Computer names
' must end with "$". Returns comma delimited string to calling code.

 Dim objTrans, objDomain, wshNetwork, strComputerName
 ' Constants for the NameTranslate object.
 Const ADS_NAME_INITTYPE_GC = 3
 Const ADS_NAME_TYPE_NT4 = 3
 Const ADS_NAME_TYPE_1779 = 1

 Set wshNetwork = CreateObject("WScript.Network")
 strComputerName = wshNetwork.ComputerName
 Set objTrans = CreateObject("NameTranslate")
 Set objDomain = getObject("LDAP://rootDse")
 objTrans.Init ADS_NAME_INITTYPE_GC, ""
 objTrans.Set ADS_NAME_TYPE_NT4, wshNetwork.UserDomain & "\" _
 & strComputerName & "$"
 szGetDN = objTrans.Get(ADS_NAME_TYPE_1779)
 'Set DN to upper Case
 szGetDN = UCase(szGetDN)
End Function

Sub UpdateNetbootGuid(guidUUID, szComputerDn)
 Dim oComputer

 'Get parentcontainer
 Set oComputer = GetObject("LDAP://" & szComputerDn)

 If ByteArrayToGuid(oComputer.netbootGuid) <> guidUUID Then
  oComputer.Put "netbootGuid", baConvertGuidToByteArray(guidUUID)
  oComputer.SetInfo
 End If

 'Clean up
  Set oComputer = Nothing
End Sub

Function ByteArrayToGuid(arrbytOctet)
If Not IsEmpty(arrbytOctet) Then
 ByteArrayToGuid = _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 4, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 3, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 2, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 1, 1))), 2) & _
  "-" & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 6, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 5, 1))), 2) & _
  "-" & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 8, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 7, 1))), 2) & _
  "-" & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 9, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 10, 1))), 2) & _
  "-"  & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 11, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 12, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 13, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 14, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 15, 1))), 2) & _
  Right("0" & Hex(AscB(MidB(arrbytOctet, 16, 1))), 2)
 End If
End Function

Function baConvertGuidToByteArray(ByVal strHexString)
 Dim fso, stream, temp, ts, n, szScrubbedString
 Set fso = CreateObject ("scripting.filesystemobject")
 Set stream = CreateObject ("adodb.stream")
 Const TemporaryFolder = 2

 temp = fso.GetSpecialFolder(TemporaryFolder) & fso.gettempname ()

 Set ts = fso.createtextfile (temp)

 szScrubbedString = Replace(strHexString, "-", "")

 ts.write Chr("&h" & Mid(szScrubbedString, 7, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 5, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 3, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 1, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 11, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 9, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 15, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 13, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 17, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 19, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 21, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 23, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 25, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 27, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 29, 2))
 ts.write Chr("&h" & Mid(szScrubbedString, 31, 2))

 ts.close

 stream.type = 1
 stream.open
 stream.loadfromfile temp

 baConvertGuidToByteArray = stream.read

 stream.close
 fso.deletefile temp

 Set stream = Nothing
 Set fso = Nothing
End Function

</VBScript>