User.Identity.Name ="empty" IIS local network , Windows authentication

I need get logged user name on my local network .We are using Windows authentication . All computers are under  same domain name.
When I set on IIS  server Anonymous Authentication                 User.Identity.Name=""
When I set on IIS  server  Windows authentication                     User.Identity.Name= IIS server name
So how can I get the current logged windows user  name on are local network at specific machine,
Thanks for any suggestion