Types of Configuration Files

Cisco IOS software uses and requires a configuration file to determine how a router is to function. Typically, network administrators enter the commands needed by the configuration file. Only two types of configuration files exist for the context of the CCNA exam:

• The running configuration file exists in RAM and contains the commands that Cisco IOS uses to drive the actions of the router.

• The startup configuration file exists in NVRAM and is the backup for the running configuration file. Startup configuration files reside in NVRAM; running configuration files exist in RAM.

As noted previously, RAM is erased when a router is powered down. Therefore, the running configuration file is erased as well.

The router will always use the running configuration file to execute. However, any time a router is restarted (cycling power or reloading the software), the running configuration file is erased and the startup configuration file is the only remaining configuration file. Therefore, during the boot sequence of a router, the router copies the startup configuration file to the running configuration file (NVRAM to RAM). Therefore, it is paramount that any time a change is made to a running configuration, the change is also copied to the startup configuration.

Be sure to know the following main operating files and where they reside:

Operating File	Memory
Basic IOS	ROM
Boot Strap	ROM
Diagnostics	ROM
Current IOS	FLASH
Startup configuration [*]	NVRAM
Running configuration	RAM

^[*] Also called backup configuration file