Rule numbering, Rule numbering step, Automatic rule numbering and renumbering – H3C Technologies H3C S6300 Series Switches User Manual

Page 13: Fragments filtering with acls, Configuration task list

Rule numbering

ACL rules can be manually numbered or automatically numbered. This section describes how automatic

ACL rule numbering works.

Rule numbering step

If you do not assign an ID to the rule you are creating, the system automatically assigns it a rule ID. The
rule numbering step sets the increment by which the system automatically numbers rules. For example, the

default ACL rule numbering step is 5. If you do not assign IDs to rules you are creating, they are

automatically numbered 0, 5, 10, 15, and so on. The wider the numbering step, the more rules you can

insert between two rules.
By introducing a gap between rules rather than contiguously numbering rules, you have the flexibility of

inserting rules in an ACL. This feature is important for a config-order ACL, where ACL rules are matched

in ascending order of rule ID.

Automatic rule numbering and renumbering

The ID automatically assigned to an ACL rule takes the nearest higher multiple of the numbering step to
the current highest rule ID, starting with 0.
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 is numbered 15. If the ACL does not contain any rule, the first rule is

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.

Fragments filtering with ACLs

Traditional packet filtering matches only first fragments of packets, and allows all subsequent non-first

fragments to pass through. Attackers can fabricate non-first fragments to attack networks.
To avoid the risks, the H3C ACL implementation does the follows:

•

Filters all fragments by default, including non-first fragments.

•

Allows for matching criteria modification, for example, filters non-first fragments only.

Configuration task list

Tasks at a glance

(Required.) Perform at least one of the following tasks:

•

Configuring a basic ACL

{

Configuring an IPv4 basic ACL

{