Reference Guide
If you enable counters on IP ACL rules that are already configured, those counters are reset when a new rule is inserted
or prepended. If a rule is appended, the existing counters are not affected. This is applicable to the following features:
• L2 Ingress Access list
• L2 Egress Access list
• L3 Egress Access list
NOTE: IP ACLs are supported over VLANs in FTOS version 6.2.1.1 and higher.
ACLs and VLANs
There are some differences when assigning ACLs to a VLAN rather than a physical port.
For example, when using a single port-pipe, if you apply an ACL to a VLAN, one copy of the ACL entries is installed in the
ACL CAM on the port-pipe. The entry looks for the incoming VLAN in the packet. Whereas if you apply an ACL on
individual ports of a VLAN, separate copies of the ACL entries are installed for each port belonging to a port-pipe.
When you use the log keyword, the CP has to log the details about the packets that match. Depending on how many
packets match the log entry and at what rate, the CP might become busy as it has to log these packets’ details.
However, the other processors (RP1 and RP2) are unaffected. This option is typically useful when debugging some
problem related to control traffic. We have used this option numerous times in the field and have not encountered
problems so far.
ACL Optimization
If an access list contains duplicate entries, FTOS deletes one entry to conserve CAM space.
Standard and extended ACLs take up the same amount of CAM space. A single ACL rule uses two CAM entries whether
it is identified as a standard or extended ACL.
Determine the Order in which ACLs are Used to Classify Traffic
When you link class-maps to queues using the service-queue command, FTOS matches the class-maps according
to queue priority (queue numbers closer to 0 have lower priorities).
As shown in the following example, class-map
cmap2
is matched against ingress packets before
cmap1
.
ACLs
acl1
and
acl2
have overlapping rules because the address range 20.1.1.0/24 is within 20.0.0.0/8. Therefore (without
the keyword order), packets within the range 20.1.1.0/24 match positive against
cmap1
and are buffered in queue 7,
though you intended for these packets to match positive against
cmap2
and be buffered in queue 4.
In cases such as these, where class-maps with overlapping ACL rules are applied to different queues, use the order
keyword to specify the order in which you want to apply ACL rules. The order can range from 0 to 254. FTOS writes to the
CAM ACL rules with lower-order numbers (order numbers closer to 0) before rules with higher-order numbers so that
packets are matched as you intended. By default, all ACL rules have an order of 254.
Example of the
order
Keyword to Determine ACL Sequence
FTOS(conf)#ip access-list standard acl1
FTOS(config-std-nacl)#permit 20.0.0.0/8
FTOS(config-std-nacl)#exit
FTOS(conf)#ip access-list standard acl2
FTOS(config-std-nacl)#permit 20.1.1.0/24 order 0
FTOS(config-std-nacl)#exit
FTOS(conf)#class-map match-all cmap1
FTOS(conf-class-map)#match ip access-group acl1
FTOS(conf-class-map)#exit
FTOS(conf)#class-map match-all cmap2
FTOS(conf-class-map)#match ip access-group acl2
FTOS(conf-class-map)#exit
FTOS(conf)#policy-map-input pmap
FTOS(conf-policy-map-in)#service-queue 7 class-map cmap1
FTOS(conf-policy-map-in)#service-queue 4 class-map cmap2
FTOS(conf-policy-map-in)#exit
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