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