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Using the boot system command

Using the boot system command
5.1.3
This page will explain how boot system commands are used to specify the fallback boot-up sequence for Cisco IOS software.
The three figures show boot system entries. These entries specify that a Cisco IOS software image will load first from flash memory, then from a network server, and finally from ROM:
  • Flash memory - A system image can be loaded from flash memory. Information stored in flash memory is not vulnerable to network failures that can occur when system images are loaded from TFTP servers. 
  • Network server - If flash memory is corrupted, a system image can be loaded from a TFTP server. 
  • ROM - The final bootstrap option is to boot from ROM. However, a system image in ROM is usually a subset of the Cisco IOS that lacks the protocols, features, and configurations of the full Cisco IOS. Also, if the software has been updated, a router may have an older version stored in ROM.  
The command copy running-config startup-config saves the commands in NVRAM. The router will execute the boot system commands as needed in the order in which they were originally entered into configuration mode.
In the Lab Activities, students will use boot system commands to display information about the Cisco IOS image and boot procedure of a router.
The next page will describe the router configuration register.

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