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说明：  ACL即访问控制列表，使用包过滤技术，在路由器上读取第三层及第四层包头中的信息如源地址、目的地址、源端口、目的端口等，根据预先定义好的规则对包进行过滤，从而达到访问控制的目的。
(ACL or access control list, use packet filtering technology, in the router to read the third layer and four Baotou source of information such as address, destination address, source port, destination port, etc., according to predefined rules packet filtering, so as to achieve the purpose of access control.)