Administrator Guide
Implementing ACL on the Dell Networking OS
You can assign one IP ACL per interface with the Dell Networking OS. If you do not assign an IP ACL to an interface, it is not used by
the software in any other capacity.
The number of entries allowed per ACL is hardware-dependent. For detailed specication on entries allowed per ACL, refer to your
line card documentation.
If you enable counters on IP ACL rules that are already congured, those counters are reset when a new rule is inserted or
prepended. If a rule is appended, the existing counters are not aected. This is applicable to the following features:
• L2 Ingress Access list
• L2 Egress Access list
• L3 Ingress Access list
• L3 Egress Access list
NOTE: IP ACLs are supported over VLANs in the Dell Networking OS version 6.2.1.1 and higher.
ACLs and VLANs
There are some dierences 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
identied as a standard or extended ACL.
Determine the Order in which ACLs are Used to Classify Trac
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 buered in queue 7, though you intended
for these packets to match positive against cmap2 and be buered in queue 4.
In cases such as these, where class-maps with overlapping ACL rules are applied to dierent 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
Access Control Lists (ACLs)
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