（接上期） 这个非常低层的信息是许多传统交换的基础，一般是被硬编码到网络硬件中的，因此更加容易识别。这样做也好也不好，因为现代人可以利用已知实体来攻击并摧毁公司网络。 传统的第三层交换和路由选择还得依靠ＩＰ地址信息，但也更容易受到外界攻击。 数据链路层的ＬＬ (Continued) This very low level of information is the basis of many traditional exchanges and is generally hardcoded into networked hardware and therefore easier to identify. It is not good to do so either because modern people can use known entities to attack and destroy the corporate network. Traditional Layer 3 switching and routing still have to rely on IP address information, but are also more vulnerable to outside attacks. LL at the data link layer