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Router boot procedure

Router boot procedure. Understanding the router memory. Router contains RAM ROM NVRAM FLASH (EEPROM) Data also stored on TFTP server. Graphic from CISCO notes. Router start-up. ROM. RAM. NVRAM. FLASH. Start up configuration. Current IOS. BOOTSTRAP BASIC IOS.

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Router boot procedure

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  1. Router boot procedure

  2. Understanding the router memory • Router contains • RAM • ROM • NVRAM • FLASH (EEPROM) • Data also stored on TFTP server

  3. Graphic from CISCO notes

  4. Router start-up ROM RAM NVRAM FLASH Start up configuration Current IOS BOOTSTRAP BASIC IOS Configuration register IOS and running-configuration needed in RAM for working router TFTP Server IOS & Configuration

  5. Router start-up • Router# show flash • looks at IOS image in flash • Router# show startup-config • looks at configuration file in NVRAM • Router# show version • looks at IOS image RAM and configuration register • o? from ROM monitor mode

  6. Router Bootstrap ROM RAM NVRAM FLASH Start up configuration Current IOS BOOTSTRAP BASIC IOS IOS Configuration register • BOOTSTRAP looks at configuration register • depending on value of least significant 4 bits • 0 uses ROM monitor mode TFTP Server IOS & Configuration • 1 uses Basic IOS from ROM • 2- F look in NVRAM for boot system settings

  7. Router default sequence • Router# configure terminal • Router(config)# boot system flash <IOS_filename> • Router(config)# boot system tftp <IOS_filename> <tftp_address> • Router(config)# boot system ROM • order of entry specifies order of fall-back sequence • Router # show running-config or show startup-config (if saved) shows the boot sequence • NOTE This requires a pre-emptive look into the startup configuration file

  8. Router default sequence What happens if boot system commands fail ? Default search sequence is used FLASH, TFTP, ROM ROM RAM NVRAM FLASH Start up configuration Current IOS BOOTSTRAP BASIC IOS Configuration register TFTP Server IOS & Configuration

  9. Router default sequence Default sequence FLASH - TFTP - ROM ROM RAM NVRAM FLASH Start up configuration Current IOS BOOTSTRAP BASIC IOS IOS Configuration register TFTP Server IOS & Configuration

  10. Configuration file next IOS has been loaded - Configuration File Next ROM RAM NVRAM FLASH Running configuration Start up configuration Current IOS BOOTSTRAP BASIC IOS IOS Configuration register IOS looks at configuration register Is ‘Ignore Configuration’ disabled ? TFTP Server IOS & Configuration YES - load configuration file from NVRAM

  11. Configuration file next IOS has been loaded - Configuration File Next ROM RAM NVRAM FLASH Start up configuration Current IOS BOOTSTRAP BASIC IOS IOS Configuration register IOS looks at configuration register Is ‘Ignore Configuration’ enabled ? TFTP Server IOS & Configuration YES - enter set-up mode

  12. Setup mode • Guided set of questions with defaults for basic router configuration • Can be invoked with the setup command • Can be bypassed (select [n] at first option or CTRL -C) • Router then enters un-configured state • Several options then exist to configure the router • Manually using configure terminal • Use a file from tftp server • Use a file from PC running hyper-terminal • Text configuration file are generated by • copy running-config tftp • show running-config (then start hyper-terminal capture mode)

  13. Configuration file loaded ROM RAM NVRAM FLASH Running configuration Start up configuration Current IOS BOOTSTRAP BASIC IOS IOS Configuration register Text file from PC with hyperterminal TFTP Server IOS & Configuration Manual Configuration

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