Implementing ACLs on Dell Networking OSYou can assign one IP ACL per interface with Dell Networking OS. If you do not assign an IP ACL to aninterface, it is not used by the software in any other capacity.The number of entries allowed per ACL is hardware-dependent. For detailed specification on entriesallowed per ACL, refer to your line card documentation.If counters are enabled on ACL rules that are already configured, those counters are reset when a newrule which is inserted or prepended or appended requires a hardware shift in the flow table. Resetting thecounters to 0 is transient as the proginal counter values are retained after a few seconds. If there is noneed to shift the flow in the hardware, the counters are not disturbed. This is applicable to the followingfeatures:• L2 Ingress Access list• L2 Egress Access listNOTE: IP ACLs are supported over VLANs in Dell Networking OS version 6.2.1.1 and higher.ACLs and VLANsThere 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 isinstalled in the ACL CAM on the port-pipe. The entry looks for the incoming VLAN in the packet. Whereasif you apply an ACL on individual ports of a VLAN, separate copies of the ACL entries are installed for eachport belonging to a port-pipe.When you use the log keyword, the CP has to log the details about the packets that match. Dependingon how many packets match the log entry and at what rate, the CP might become busy as it has to logthese packets’ details. However, the other processors (RP1 and RP2) are unaffected. This option istypically useful when debugging some problem related to control traffic. We have used this optionnumerous times in the field and have not encountered problems so far.ACL OptimizationIf an access list contains duplicate entries, Dell Networking OS 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 CAMentries whether it is identified as a standard or extended ACL.Determine the Order in which ACLs are Used to Classify TrafficWhen you link class-maps to queues using the service-queue command, Dell Networking OS matchesthe 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 againstcmap1 and are buffered in queue 7, though you intended for these packets to match positive againstcmap2 and be buffered in queue 4.In cases such as these, where class-maps with overlapping ACL rules are applied to different queues, usethe order keyword to specify the order in which you want to apply ACL rules. The order can range from0 to 254. Dell Networking OS writes to the CAM ACL rules with lower-order numbers (order numbers94 Access Control Lists (ACLs)
