The operating system used in almost all Cisco devices is the Cisco Internetwork Operating System (IOS). The Cisco IOS® is the software that allows the hardware to function as a router or switch. The IOS file is several megabytes.

The software a router or switch uses is referred to as the configuration file or the config. The configuration contains the “instructions” that define how the device is to route or switch. A network administrator creates a configuration that defines the desired functionality of the Cisco device. The functions that can be specified by the configuation are the IP addresses of the interfaces, routing protocols, and networks to be advertised. The configuration file typically is a few hundred to a few thousand bytes.

Each of the software components is stored in memory as a separate file. These files are also stored in different types of memory.

The IOS is stored in a memory area called flash. Flash memory provides non-volatile storage of an IOS that can be used as an operating system at startup. The flash allows the IOS to be upgraded or stores multiple IOS files. In many router architectures, the IOS is copied into and run from Random Access Memory (RAM).

A copy of the configuration file is stored in Non-volatile RAM (NVRAM) to be used as a configuration during startup. This is referred to as the “startup config”. The startup configuration is copied into RAM at boot time. This configuration in RAM is the configuration used to operate the router. It is referred to as the “running config”.

Beginning with version 12 of the IOS, a single interface to all the file systems that a router uses is provided. This is referred to as the Cisco IOS File System (IFS). The IFS provides a single method to perform all the file system management that a router uses. This would include the flash memory file systems, the network file systems (TFTP, rcp, and FTP), and reading or writing data (such as NVRAM, the running configuration, ROM). The IFS uses a common set of prefixes to specify file system devices.

The IFS uses the URL convention to specify files on network devices and the network. The URL convention identifies the location of the configuration files following the colon as [[[//location]/directory]/filename]. The IFS also supports FTP file transfer.

Interactive Media Activity Drag and Drop: IOS File System Overview When the student has completed this activity, the student will be able to list the configuration files and their locations.