Administrator Guide

Test CAM Usage

This command applies to both IPv4 and IPv6 CAM profiles, but is best used when verifying QoS optimization for IPv6 ACLs.

To determine whether sufficient ACL CAM space is available to enable a service-policy, use this command. To verify the actual CAM

space required, create a class map with all the required ACL rules, then execute the test cam-usage command in Privilege mode. The

following example shows the output when executing this command. The status column indicates whether you can enable the policy.

Example of the test cam-usage Command

DellEMC#test cam-usage service-policy input asd stack-unit 1 port-set 0

--------------------------------------------------------------------------

1| 1| IPv4Flow| 232| 0|Allowed

DellEMC#

Implementing ACLs on Dell EMC 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

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. Effective 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.

NOTE:

System access lists (system-flow entries) are pre-programmed in the system for lifting the control-plane

packets destined for the local device which the CPU needs to process. The system access lists always override the user

configured access lists. Even if you configure ACL to block certain hosts, control plane protocols such as, ARP, BGP,

LACP, VLT, VRRP and so on, associated with such hosts cannot be blocked.

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 EMC 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 EMC 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.

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Access Control Lists (ACLs)