So I noticed a nice feature on my ASR 1006 that I was configuring in the lab today and wondered if the feature was also available on ISR’s as well. I did some looking and noticed that it also available on that family as well. The feature is known as Configuration Generation Performance Enhancement and is available for ISR’s starting in 12.3(7)T and beyond. The feature assists configuration management by enabling faster collection of running configuration file information. This feature is especially useful in managing large networks with numerous interfaces configured. So here’s how it works:

In the Cisco IOS software configuration model, the configuration state is maintained in a distributed manner, with each component storing its own configuration state. To retrieve configuration information, the software must poll every component to collect the distributed information. This configuration state retrieval operation is performed by a process known as nonvolatile generation (NVGEN), and it is used by command-line interface (CLI) commands such as show running-configuration, write memory, and copy system:running-configuration to display or copy the running system configuration. When invoked, NVGEN queries each system component and each instance of interface or other configuration objects. A running configuration file is constructed as NVGEN traverses the system performing these queries.

Before the Configuration Generation Performance Enhancement feature was introduced, NVGEN always had to query the entire system and could generate only a total configuration. The time required to process the running configuration creates performance problems for configuration management, because completion of the NVGEN operation can take many minutes. The Configuration Generation Performance Enhancement feature reduces the execution time for NVGEN processes and is especially useful for managing large configuration files that contain numerous interface configurations.

This feature provides faster execution of commands that process the running system configuration by caching interface configuration information in system memory, and by retrieving only configuration information that has changed.

Configuring the feature is relatively easy. All that needs to be done to enable the feature is the following:

1841#config t
Enter configuration commands, one per line. End with CNTL/Z.
1841(config)#parser config cache interface
1841(config)#end
1841#

You can verify that the parser config cache interface command has been enabled by checking for the command in the system configuration file displayed when you enter the show running-configuration EXEC command.

1841#sh running-config
Load for five secs: 1%/0%; one minute: 1%; five minutes: 1%
Time source is NTP, 11:41:19.516 CDT Wed Sep 17 2008

Building configuration...

Current configuration : 7483 bytes
!
! Last configuration change at 11:38:10 CDT Wed Sep 17 2008 by CCIE6200
! NVRAM config last updated at 11:05:23 CDT Wed Sep 17 2008 by CCIE6200
!
version 12.4
parser config cache interface

The first time you display the configuration file, you will not see much evidence of improvement in performance because the interface cache will be filled up. However, you will notice performance improvements when you enter subsequent NVGEN-type commands such as the show running-configuration EXEC command.