| Lab Activity 9.3.11: Booting up the router Cisco routers boot Cisco IOS software from: Flash TFTP server ROM (not full Cisco IOS) Multiple source options provide flexibility and fallback alternatives Locating the Cisco IOS Software Default source for Cisco IOS software: Flash (sequential) TFTP server (netboot) ROM (partial IOS) Note: boot system commands can be used to specify the primary IOS source and fallback sequences. Booting up the router and locating the Cisco IOS. ROM POST Bootstrap code executed Check Configuration Register value (NVRAM) which can be modified using the config-register command 0 = ROM Monitor mode 1 = ROM IOS 2 - 15 = startup-config in NVRAM Startup-config file: Check for boot system commands (NVRAM) If boot system commands in startup-config Run boot system commands in order they appear in startup-config to locate the IOS [If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)?] If no boot system commands in startup-config use the default fallback sequence in locating the IOS: Flash (sequential) TFTP server (netboot) ROM (partial IOS) or keep retrying TFTP depending upon router model If IOS is loaded, but there is no startup-config file, the router will use the default fallback sequence for locating the IOS and then it will enter setup mode or the setup dialogue. If no IOS can be loaded, the router will get the partial IOS version from ROM