访问控制列表（ACL）分为基本和高级两种。下面关于ACL的描述中，正确的是（）。
- A.基本访问控制列表基于源IP地址
- B.ACL的默认执行顺序是自下而上
- C.进入需要应用的接口时使用 ip access-group命令启动基本访问控制表
- D.编号范围是从1099到1199的访问控制列表是高级IP访问控制列表
正确答案及解析
正确答案
解析
访问控制列表（Access Control Lists，ACL）是目前使用最多的访问控制实现技术。访问控制列表是路由器接口的指令列表，用来控制端口进出的数据包。ACL适用于所有的被路由协议，如IP、IPX、AppleTalk等。访问控制列表可以分为基本访问控制列表和高级访问控制列表。ACL的默认执行顺序是自上而下，在配置时要遵循最小特权原则、最靠近受控对象原则及默认丢弃原则。
（1）基本访问控制列表
基本访问控制列表基于IP地址，列表取值为2000～2999，分析数据包的源地址决定允许或拒绝数据报通过。
（2）高级访问控制列表
高级IP访问控制列表比基本IP访问控制列表具有更多的匹配项，包括协议类型、源地址、目的地址、源端口、目的端口、建立连接的和IP优先级等。编号范围是从3000到3999的访问控制列表是高级IP访问控制列表。
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