thx lonkero, but it seems not to work [Frown]

so i wrote this; it works good:

code:
 
:winnt


if 0=exist("%windir%\ipchanged.tmp")

$bkey="HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters"

$NewIP="255.255.0.0."

$c=0

$Reboot = 0

$KeyN = enumkey("$bkey\Interfaces\",$c)

	while @error = 0
		$ip = ReadValue($bkey+"\Interfaces\$KeyN","SubnetMask")
		if @error = 0 and $ip <> "0.0.0.0"
			$ = writevalue($bkey+"\Interfaces\$KeyN","SubnetMask",$newIP,"REG_MULTI_SZ")
			$Reboot = 1
		endif
		$c = $c +1
		$KeyN = enumkey($bkey+"\Interfaces\",$c)
	loop
	if $Reboot = 1
		shell "%comspec% /c echo changed ip from 255.255.255.0 to 255.255.0.0 > %windir%\ipchanged.tmp"
		? "SubnetMask Changed"
		? ? "  Press any key to quit..." get $
		SHUTDOWN ("","Redemarrage",5,1,1)
	else
		shell "%comspec% /c echo no changes done > %windir%\ipchanged.tmp"
	endif
endif