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Cisco File Systems Overview

The Cisco IOS image is a file stored in the router's flash memory. IOS management involves understanding the IOS file system, which is similar to computer operating system file systems, such as Windows, Linux, and UNIX. 

Similar to web addresses, it allows Cisco IOS and administrators to use URLs to store, retrieve, and manipulate files. For instance, Cisco routers and switches use URLs with prefixes like "flash:" or "ftp:" to locate files locally or on remote servers.

NOTE: Various Cisco operating systems, including Cisco IOS and NX-OS, share comparable command sets and system configuration methods. Yet, distinctions exist in commands and functionalities. Discrepancies may also arise among various software versions.

In addition, Cisco IOS devices offer the Cisco IOS Integrated File System (IFS), allowing simple and efficient file and directory handling. It unifies various file systems, including flash memory, network systems (TFTP, RCP, FTP), and other available memory (NVRAM, RAM) for data storage and retrieval. The Cisco IFS employs URLs to indicate file locations on both network devices and the network, using a specific URL prefix.

Commonly used prefixes are:

  • Flash: The primary memory where the software image is stored by default, for instance, “flash:/c2900-universalk9-mz.SPA.154-1T.bin”. Some devices have multiple flash locations, such as slot0 and slot1. 
  • NVRAM: Non-Volatile Random Access Memory is a type of memory that retains stored data even when the power is turned off. Therefore, this is where devices keep the startup configuration, for instance, “nvram:/startup-config,” which needs to persist across reboots or power cycles.
  • System: A partition built into the RAM that holds the running configuration, among other things. For example, “system:/running-config.”
  • TFTP: Indicates that the file is stored on a server that can be accessed using the Trivial File Transfer Protocol.
  • FTP: Indicates that the file is stored on a server that can be accessed using the File Transfer Protocol.
  • SCP: Indicates that the file is stored on a server that can be accessed using the Secure Copy Protocol. This is the preferred method when security is the main concern. 

Various supported file systems on a Cisco router

As you can see from the image above, various file systems are supported on a Cisco device. You can also create backups of the image file and the running configuration in different locations when required. 

You can use the “show file systems” command to get details on the file systems. It provides information on the available file systems, memory information, file system type, and permissions, such as read-only, write-only, or read-write.