The running configuration file reflects the current configuration applied to a Cisco IOS device. It contains the commands used to determine how the device operates on the network, as shown in Figure 1. Modifying a running configuration affects the operation of a Cisco device immediately.

The running configuration file is stored in the working memory of the device, or random access memory (RAM). This means that the running configuration file is temporarily active while the Cisco device is running (powered on). However, if power to the device is lost or if the device is restarted, all configuration changes will be lost unless they have been saved.

After making changes to a running configuration file, consider these distinct options:

The startup configuration file reflects the configuration that will be used by the device upon reboot. The startup configuration file is stored in NVRAM. When a network device has been configured and the running configuration has been modified, it is important to save those changes to the startup configuration file. Doing so prevents changes from being lost due to power failure or a deliberate restart.

Before committing to the changes, use the appropriate show commands to verify the device's operation. As shown in the figure, the show running-config command can be used to see a running configuration file. When the changes are verified to be correct, use the copy running-config startup-config command at the privileged EXEC mode prompt. The command to save the running configuration to startup configuration file is:

Switch# copy running-config startup-config

After being executed, the running configuration file updates the startup configuration file.

If the changes made to the running configuration do not have the desired effect, it may become necessary to restore the device to its previous configuration. Assuming that we have not overwritten the startup configuration with the changes, we can replace the running configuration with the startup configuration. This is best done by restarting the device using the reload command at the privileged EXEC mode prompt.

When initiating a reload, the IOS will detect that the running config has changes that were not saved to startup configuration. A prompt will appear to ask whether to save the changes made. To discard the changes, enter n or no.

An additional prompt will appear to confirm the reload. To confirm, press Enter. Pressing any other key will abort the process.

For example:

Switch# reload

System configuration has been modified. Save? [yes/no]: n

Proceed with reload? [confirm]

*Apr 13 01:34:15.758: %SYS-5-RELOAD: Reload requested by console. Reload Reason:

Reload Command.

System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 2004 by cisco Systems, Inc.

PLD version 0x10

GIO ASIC version 0x127

c1841 processor with 131072 Kbytes of main memory

Main memory is configured to 64 bit mode with parity disabled

If undesired changes are saved to the startup configuration, it may be necessary to clear all the configurations. This requires erasing the startup configuration and restarting the device.

The startup configuration is removed by using the erase startup-config command.

To erase the startup configuration file use erase NVRAM:startup-config or erase startup-config at the privileged EXEC mode prompt:

Switch# erase startup-config

After the command is issued, the switch will prompt you for confirmation:

Erasing the nvram filesystem will remove all configuration files! Continue? [confirm]

Confirm is the default response. To confirm and erase the startup configuration file, press Enter. Pressing any other key will abort the process.

Caution: Exercise caution when using the erase command. This command can be used to erase any file in the device. Improper use of the command can erase the IOS itself or another critical file.

On a switch you must also issue the delete vlan.dat command in addition to the erase startup-config command in order to return the device to its default "out-of-the-box" configuration (comparable to a factory reset):

Switch# delete vlan.dat

Delete filename [vlan.dat]?

Delete flash:vlan.dat? [confirm]

Switch# erase startup-config

Erasing the nvram filesystem will remove all configuration files! Continue? [confirm]

[OK]

Erase of nvram: complete

Switch#

After removing the startup configuration from NVRAM (and deleting the vlan.dat file in the case of a switch), reload the device to remove the current running configuration file from RAM. The device will then load the default startup configuration that was originally shipped with the device into the running configuration.

In Figure 2, practice entering commands to save the running configuration from RAM to NVRAM.