Concept Guide

after a few seconds. If there is no need to shift the ow in the hardware, the counters are not aected. This is applicable to the following
features:
• L2 Ingress Access list
• L2 Egress Access list
In the Dell EMC Networking OS versions prior to 9.13(0.0), the system does not install any of your ACL rules if the available CAM space is
lesser than what is required for your set of ACL rules. Eective with the Dell EMC Networking OS version 9.13(0.0), the system installs your
ACL rules until all the allocated CAM memory is used. If there is no implicit permit in your rule, the Dell EMC Networking OS ensures that an
implicit deny is installed at the end of your rule. This behavior is applicable for IPv4 and IPv6 ingress and egress ACLs.
ACLs and VLANs
There are some dierences 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.
ACL Optimization
If an access list contains duplicate entries, the system 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 identied as a
standard or extended ACL.
Determine the Order in which ACLs are Used to
Classify Trac
When you link class-maps to queues using the service-queue command, the system 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 buered in queue 7, though you intended for these
packets to match positive against cmap2 and be buered in queue 4.
In cases such as these, where class-maps with overlapping ACL rules are applied to dierent 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. The Dell Networking OS 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 255.
Example of the order Keyword to Determine ACL Sequence
Dell(conf)#ip access-list standard acl1
Dell(config-std-nacl)#permit 20.0.0.0/8
Dell(config-std-nacl)#exit
Dell(conf)#ip access-list standard acl2
Dell(config-std-nacl)#permit 20.1.1.0/24 order 0
Dell(config-std-nacl)#exit
Dell(conf)#class-map match-all cmap1
Dell(conf-class-map)#match ip access-group acl1
Dell(conf-class-map)#exit
Dell(conf)#class-map match-all cmap2
Dell(conf-class-map)#match ip access-group acl2
Dell(conf-class-map)#exit
Dell(conf)#policy-map-input pmap
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Access Control Lists (ACLs)