asp.net获取真实ip

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;
    }