H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 10)

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NOTE:
A wildcard mask, also called an “inverse mask,” is a 32-bit binary and represented in dotted decimal
notation. In contrast to a network mask, the 0 bits in a wildcard mask represent ‘do care’ bits, and the 1
bits represent ‘don’t care’ bits. If the 'do care' bits in an IP address are identical to the ‘do care’ bits in an
IP address criterion, the IP address matches the criterion. All ‘don’t care’ bits are ignored. The 0s and 1s
in a wildcard mask can be noncontiguous. For example, 0.255.0.255 is a valid wildcard mask.
ACL rule comments
You can add a comment about an ACL rule to make it easy to understand. The rule comment appears
below the rule statement.
ACL rule numbering
What is the ACL rule numbering step
If you do not assign an ID for 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
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 avoids the risks, the H3C ACL implementation:
• Filters all fragments by default, including non-first fragments.
• Allows for matching criteria modification, for example, filters non-first fragments only.