1.In IIS7, browse to the directory containing your public.asmx and private.asmx files.
2.The title at the top will reflect the current directory, like "WebService Home". Click the "Content View" button at the bottom.
3.Right-click on your public.asmx file and choose "Switch to Features View".
4.The title should be "public.asmx Home" to confirm that you're managing the one file.
5.Add your IP restrictions. In this case, I think you want an Allow entry for 127.0.0.1 and choose "Edit Feature Settings" from the Action menu to Deny access to unspecified clients.
6.Click your containing folder again (e.g. WebService) and switch to Content View again to repeat these steps on private.asmx.
Very strange UX!?!