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Cisco uBR924 Software Configuration Guide
OL-0337-05 (8/2002)
Appendix A Using Cisco IOS Software
Understanding Cisco IOS Configuration Files
Startup and Run-Time Configuration Files
The startup configuration file is a Cisco IOS configuration file stored in the router’s non-volatile Flash
memory and is automatically run whenever the router is reset or powered-on. When a DOCSIS
configuration file specifies that a Cisco IOS configuration file should be downloaded, that Cisco IOS
configuration file automatically becomes the startup configuration file.
The run-time configuration file is the Cisco IOS configuration file that the router is currently using as it
operates. When a router is first powered-on or reset, the run-time configuration file is the same as the
startup configuration file.
However, when you make configuration changes to the router, either by using the CLI or by using SNMP
commands, the run-time configuration file is updated with those changes. Over time, the run-time
configuration file has a different configuration than the startup configuration file. Resetting the router
automatically erases the run-time configuration and restores the startup configuration.
If you want to save your changes to the router’s configuration, you must save the run-time configuration
as the startup configuration file. To do so, enter the following global configuration command:
copy running-config startup-config
Note Any changes you make to either the startup or run-time configuration are automatically overwritten
when the router is rebooted if the DOCSIS configuration file specifies that a new Cisco IOS
configuration file must be downloaded from the TFTP server. If this is the case, you must also manually
update the Cisco IOS configuration file on the TFTP server to preserve any configuration changes you
make.
To restore the startup configuration without resetting the router, give the following global configuration
command:
copy startup-config running-config
Displaying the Configuration Files
The startup and run-time configuration files can be displayed with the following global configuration
commands:
show startup-config
show running-config
The Cisco uBR924 router displays the appropriate configuration file in a format that you can capture and
save on a TFTP server so it can be downloaded to another router.
Note The configuration files do not contain any commands that restore the router to its default values. For
example, if you enable IP routing with the “ip routing” command, this is not saved in the configuration
files because this is the default configuration. However, if you disable IP routing with the “no ip
routing” command, this is saved in the configuration file.
The show command uses exclamation marks (!) to create blank lines as spacers. These extra lines do not
affect the functionality of the router but exist only to make the configuration files more readable.