在CCNA和NP中我们了解到了ACL――思科为网络访问提供的一种安全手段，它是运行在CISCO的IOS上的一种程序。传统的ACL分三大类：标准ACL/扩展ACL/命名ACL.这里对其做简单的回顾：
Cisco routers can identify access-list using two methods：
access-list number――the number of the access list determines what protocol it is filtering：
――(1-99)and(1300-1399)―― standard IP access list
――(100-199)and(2000-2699)―― extended IP access list
access list name (IOS versions gt 11.2)
Names contain alphanumeric characters
Names connot contain spaces or punctuation and must begin with alphabetic character
名称访问列表可以包含数字和字母，但其不可以包含空格及标点符号，而且第一个字符要是字母。
Cisco router support two basic types of IP access lists：
――standard――Filter IP packets based on the source address only.
标准访问列表针对源IP地址进行过滤
――Extended――Fiter IP packets based on several attributes.including：
――Protocol type.
――Source and desination IP address
――Source and destination TCP/UDP ports
――ICMP and IGMP message types.
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