Tim Van Wassenhove

A while ago i wrote that i had created two .reg files to update my Internet Options / Lan Settings (Automating the configuration of Internet Options / Lan Settings). Yesterday i build a little Windows Service that automates this completely. With NotifyAddrChange i am notified whenever a change occurs in the table that maps IPv4 addresses to interfaces:

[DllImport("iphlpapi.dll", CharSet = CharSet.Ansi)]
private static extern int NotifyAddrChange(ref IntPtr handle, IntPtr overlapped);

The main loop of the service looks like this:

while (this.isRunning)
{
 IntPtr handle = IntPtr.Zero;
 NotifyAddrChange(ref handle, IntPtr.Zero);
 UpdateRegistry();
}

Whenever i’m connected to the LAN at work i want to use a proxy. Here’s the code that takes care of this:

private static void UpdateRegistry()
{
 RegistryKey registryKey = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Internet Settings", true);
 if (IsInWorkLan())
 {
  registryKey.SetValue("AutoConfigURL", "http://123.456.789.0");
 }
 else
 {
  registryKey.DeleteValue("AutoConfigURL", false);
 }
}

Figuring out whether i’m connected to the LAN at work is pretty simple. As soon as i have an IPAddress that looks like 192.168.X.Y i’m connected. Here’s how i translated this into code:

private static bool IsInWorkLan()
{
 foreach (IPAddress ipAddress in Dns.GetHostAddresses(Dns.GetHostName()))
 {
  if (IsInWorkLan(ipAddress))
  {
   return true;
  }
 }

 return false;
}

private static bool IsInWorkLan(IPAddress ipAddress)
{
 byte[] bytes = ipAddress.GetAddressBytes();
 if ((int)bytes[0] == 192 && (int)bytes[1] == 168)
 {
  return true;
 }

 return false;
}