47-9
Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 47 Configuring Network Security with ACLs
TCAM Programming and ACLs for Supervisor Engine II-Plus, Supervisor Engine IV, Supervisor Engine V, and
This is a summary of scenarios that cause TCAM utilization to change:
Adding or deleting ACLs or ACEs in the running-config
Copying or recopying the ACL configuration from bootflash, a TFTP server, or CompactFlash
memory to the running-config
Changing the TCAM programming algorithm
Saving the running-config to NVRAM and reloading the switch
Resizing the feature ACL or QoS regions of the TCAM by using the
access list hardware region [feature | qos] [input | output] balance percent command on
Cisco IOS Release 12.2(31)SGA and later.
Upgrading from images based on Cisco IOS Release 12.2(25)EWA to images based on Cisco IOS
Release 12.2(31)SGA
Two types of hardware resources are consumed when you program ACLs: entries and masks. If either
one of these resources is exhausted, no additional ACLs can be programmed into hardware.
If you run out of resources, refer to the following sections:
Changing the Programming Algorithm, page 47-9
Resizing the TCAM Regions, page 47-11
Selecting Mode of Capturing Control Packets, page 47-13
Changing the Programming Algorithm
If the masks on a system are exhausted, but entries are available, changing the programming scheme
from packed to scattered might free up masks, allowing additional ACLs to be programmed into
hardware.
Note Changing the ACL programming algorithm or resizing the TCAM regions causes all ACLs to be
temporarily unloaded from the hardware and then reloaded in accordance with the new TCAM
parameters. ACLs are inoperative until the reloading process is complete.
The goal is to use TCAM resources more efficiently by minimizing the number of masks per ACL entry.
The following table shows how to change the algorithm that controls TCAM utilization:
Task... Command...
Compare TCAM utilization when using
the scattered or packed algorithms.
Switch# show platform hardware acl statistics
utilization brief
Change the algorithm from packed to
scattered.
Switch(config)# access-list hardware entries
scattered
Change the algorithm from scattered to
packed.
Switch(config)# access-list hardware entries
packed