Reference Guide

66 | Access Control Lists (ACLs)
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Implementing ACLs on FTOS
One IP ACL can be assigned per interface with FTOS. If an IP ACL is not assigned to an interface, it is not
used by the software in any other capacity.
The number of entries allowed per ACL is hardware-dependent. Refer to your line card documentation for
detailed specification on entries allowed per ACL.
If counters are enabled on ACL rules that are already configured, those counters are reset when a new rule
which is inserted or prepended or appended requires a hardware shift in the flow table. Resetting the
counters to 0 is transient as the proginal counter values are retained after a few seconds. If there is no need
to shift the flow in the hardware, the counters are not disturbed. This is applicable to the following
features:
• L2 Ingress Access list
• L2 Egress Access list
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 would get
installed in the ACL CAM on the port-pipe. The entry would look 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 would be
installed for each port belonging to a port-pipe.
Determine the order in which ACLs are used to classify traffic
When you link class-maps to queues using the command service-queue, FTOS matches the class-maps
according to queue priority (queue numbers closer to 0 have lower priorities). For example, in Figure 6-1,
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, as shown in Figure 6-1. 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.
V
Note: IP ACLs are supported over VLANs in Version 6.2.1.1 and higher.