穿过代理服务器取远程用户真实IP地址

public static string GetIP()
      {
          string str = "";
          //穿过代理服务器取远程用户真实IP地址：
          if (System.Web.HttpContext.Current.Request.ServerVariables["HTTP_VIA"] != null)
          {
              str = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"].ToString();
          }
          else
          {
              str = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"].ToString();
          }
          return str;
      }