Implementing time-based acl rules, Fragments filtering with acls, Acl configuration task list – H3C Technologies H3C S5120 Series Switches User Manual

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For 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 rule

will be numbered 0.

Whenever the step changes, the rules are renumbered, starting from 0. For example, if there are five

rules numbered 5, 10, 13, 15, and 20, changing the step from 5 to 2 causes the rules to be renumbered

0, 2, 4, 6 and 8.

Likewise, after you restore the default step, ACL rules are renumbered in the default step. Assume that

there are four ACL rules numbered 0, 2, 4, and 6 in steps of 2. When the default step is restored, the

rules are renumbered 0, 5, 15, and 15.

Implementing Time-Based ACL Rules

You can implement ACL rules based on the time of day by applying a time range to them. A time-based

ACL rule takes effect only in any time periods specified by the time range.

Two basic types of time range are available:

Periodic time range, which recurs periodically on a day or days of the week.

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 time

range can take effect only after you define the time range.

Fragments Filtering with ACLs

Traditional packet filtering matched only first fragments of IPv4 packets, and allowed all subsequent

non-first fragments to pass through. This mechanism resulted in security risks, because attackers may

fabricate non-first fragments to attack networks.

As for the configuration of a rule of an ACL, the fragment keyword specifies that the rule applies to

non-first fragment packets only, and does not apply to non-fragment packets or the first fragment

packets. ACL rules that do not contain this keyword is applicable to both non-fragment packets and

fragment packets.

ACL Configuration Task List

Complete the following tasks to configure an ACL:

Task

Remarks

Creating a Time Range

Optional

Required

Configure at least one task

Optional

Optional