1-4For example, if the numbering step is 5 (the default), and there are five ACL rules numbered 0, 5, 9, 10,and 12, the newly defined rule will be numbered 15. If the ACL does not contain any rule, the first rulewill be numbered 0.Whenever the step changes, the rules are renumbered, starting from 0. For example, if there are fiverules numbered 5, 10, 13, 15, and 20, changing the step from 5 to 2 causes the rules to be renumbered0, 2, 4, 6 and 8.Likewise, after you restore the default step, ACL rules are renumbered in the default step. Assume thatthere are four ACL rules numbered 0, 2, 4, and 6 in steps of 2. When the default step is restored, therules are renumbered 0, 5, 15, and 15.Implementing Time-Based ACL RulesYou can implement ACL rules based on the time of day by applying a time range to them. A time-basedACL rule takes effect only in any time periods specified by the time range.Two basic types of time range are available:z Periodic time range, which recurs periodically on a day or days of the week.z Absolute time range, which represents only a period of time and does not recur.You may apply a time range to ACL rules before or after you create it. However, the rules using the timerange can take effect only after you define the time range.Fragments Filtering with ACLsTraditional packet filtering matched only first fragments of IPv4 packets, and allowed all subsequentnon-first fragments to pass through. This mechanism resulted in security risks, because attackers mayfabricate non-first fragments to attack networks.As for the configuration of a rule of an ACL, the fragment keyword specifies that the rule applies tonon-first fragment packets only, and does not apply to non-fragment packets or the first fragmentpackets. ACL rules that do not contain this keyword is applicable to both non-fragment packets andfragment packets.ACL Configuration Task ListComplete the following tasks to configure an ACL:Task RemarksCreating a Time Range OptionalConfiguring a Basic ACLConfiguring an Advanced ACLConfiguring an Ethernet Frame Header ACLRequiredConfigure at least one taskCopying an ACL OptionalApplying an ACL for Packet Filtering Optional
