asp.net获取真实ip的方法

public string getip()
{
  string result = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
  if (null == result || result == String.Empty)
  {
   result = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
  }
  if (null == result || result == String.Empty)
  {
   result = HttpContext.Current.Request.UserHostAddress;
  }
  return result;
}