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Hack 43 Change from Static IP to DHCP
Reconfiguring a network from static IP
addressing to DHCP is a chore no system administrator wants to do,
but now there's help.
Companies grow over time, and their networks have to grow along with
them. This means that the static IP addressing that was used when
the network was small will no longer practical once the systems
number more than a few dozen. Unfortunately, changing machines from
static to dynamic addressing usually means visiting each machine,
logging on as a local administrator, and clicking through numerous
properties sheets to reconfigure TCP/IP settings for network
adapters.
However, there's an easier way. The VBScript in this
hack uses Registry writes to change the TCP/IP settings on a machine
from static IP to DHCP.
The Code
Type the script into
Notepad (with Word Wrap disabled) and save it with a .vbs
extension as Static2DHCP.vbs:
'All variables declared
Option Explicit
Dim oWSHShell
Dim sNIC, sMan
Dim iCount
Set oWSHShell = WScript.CreateObject("WScript.Shell")
' Set the DCHP service to autostart
oWSHShell.RegWrite "HKLM\SYSTEM\CurrentControlSet\Services\DHCP\Start", 2
' Get Network card
On Error Resume Next
iCount = 1
Do
sNIC = oWSHShell.RegRead("HKLM\SOFTWARE\Microsoft\Windows NT\ " & _
"CurrentVersion\NetworkCards\" & iCount & "\ServiceName")
sMan = oWSHShell.RegRead("HKLM\SOFTWARE\Microsoft\Windows NT\ " & _
"CurrentVersion\NetworkCards\" & iCount & "\Manufacturer")
' Skip the Async and NDIS services
If sMan <> "Microsoft" And Err.Number = 0 Then
Call SetNIC
End If
iCount = iCount + 1
Loop Until Err.Number <> 0
' Clear the error
Err.Clear
' End of Script
Sub SetNIC
Dim iTest
' Set the NIC service to use DHCP
sNIC = "HKLM\SYSTEM\CurrentControlSet\Services\" & sNIC &"\Parameters\TCPIP\"
iTest = oWSHShell.RegRead(sNIC & "EnableDHCP")
If iTest = 0 Then
oWSHShell.RegWrite sNIC & "EnableDHCP", 1, "REG_DWORD"
oWSHShell.RegWrite sNIC & "IPAddress", "0.0.0.0", "REG_MULTI_SZ"
oWSHShell.RegWrite sNIC & "SubnetMask", "0.0.0.0", "REG_MULTI_SZ"
End If
End Sub
Running the Hack
To run this hack, call the Static2DHCP.vbs
script from a logon script and use Group Policy to assign
this logon script to users' machines. When a user
next logs on to his machine, the machine's TCP/IP
settings will be changed from static to dynamic addressing. To lease
an address from the DHCP server, the user's machine
needs to be rebooted, so you could also send out a message asking all
users to reboot their machines using the method in [Hack #35] or some other approach. If
you like, the logon script could also be combined with the
SU utility from the Windows 2000 Server Resource
Kit to perform a hands-off migration from static to dynamic
addressing.
Rod Trent
