Depth-first match for an Ethernet frame header ACL
The following shows how your device performs depth-first match in an Ethernet frame header ACL:
Sort rules by source MAC address mask first and compare packets against the rule configured with
more ones in the source MAC address mask.
If two rules are present with the same number of ones in their source MAC address masks, look at
the destination MAC address masks. Then, compare packets against the rule configured with more
ones in the destination MAC address mask.
If the numbers of ones in the destination MAC address masks are the same, compare packets
against the one configured first.
The comparison of a packet against ACL rules stops immediately after a match is found. The packet is
then processed as per the rule.
IPv4 ACL Step
Meaning of the step
The step defines the difference between two neighboring numbers that are automatically assigned to
ACL rules by the device. For example, with a step of 5, rules are automatically numbered 0, 5, 10, 15,
and so on. By default, the step is 5.
Whenever the step changes, the rules are renumbered, starting from 0. For example, if four rules are
numbered 5, 10, 15, and 20 respectively, changing the step from 5 to 2 will cause the rules to be
renumbered 0, 2, 4, and 6.
Benefits of using the step
With the step and rule numbering/renumbering mechanism, you do not need to assign numbers to rules
when defining them. The system will assign a newly defined rule a number that is the smallest multiple
of the step bigger than the current biggest number. For example, with a step of five, if the biggest
number is currently 28, the newly defined rule will get a number of 30. If the ACL has no rule defined
already, the first defined rule will get a number of 0.
Another benefit of using the step is that it allows you to insert new rules between existing ones as
needed. For example, after creating four rules numbered 0, 5, 10, and 15 in an ACL with a step of five,
you can insert a rule numbered 1.
Effective Period of an IPv4 ACL
You can control when a rule can take effect by referencing a time range in the rule.
A referenced time range can be one that has not been created yet. The rule, however, can take effect
only after the time range is defined and becomes active.
IP Fragments Filtering with IPv4 ACL
Traditional packet filtering performs match operation only on first fragments. All subsequent non-first
fragments are allowed to pass through. As attackers may fabricate non-first fragments to attack your
network, this results in security risks.
As for the configuration of a rule of an IPv4 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