Implementing Acls On Dell Networking Os - Dell S4048–ON Configuration Manual

Implementing ACLs on Dell Networking OS

You can assign one IP ACL per interface. If you do not assign an IP ACL to an interface, it is not used by the software.
The number of entries allowed per ACL is hardware-dependent.
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 affected. This is
applicable to the following features:
• L2 Ingress Access list
• L2 Egress Access list
NOTE: IP ACLs are supported over VLANs in Dell Networking OS version 6.2.1.1 and higher.
Assigning ACLs to VLANs
When you apply an ACL to a VLAN using single port-pipe, a copy of the ACL entries gets installed in the ACL CAM on the port-pipe.
The entry looks for the incoming VLAN in the packet. When 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.
You can use the log keyword to log the details about the packets that match. The control processor becomes busy based on the
number of packets that match the log entry and the rate at which the details are logged in. However, the route processor (RP) is
unaffected. You can use this option for debugging issues related to control traffic.
ACL Optimization
If 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 CAM entries to identify whether
the access list is 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, Dell Networking OS 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 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. 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 Keyword to Determine ACL Sequence
order
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
Dell(conf-policy-map-in)#service-queue 7 class-map cmap1
Access Control Lists (ACLs)
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