boot sequence for IOS when config reg is 2102

bertbloggs

I am reading conflicting info about the boot sequence of a Cisco router .

I have a CD document which states "2102 means boot from NVRAM, Flash, or the network. 2102 defaults to Flash, if the router contains Flash memory"
As opposed to this the Todd Lammie book states "2102 tells the router to use the boot commands specified in NVRAM"

My interpretation is that 2102 means "check NVRAM to see if there is a boot system instruction, if yes then use it, if not boot from Flash"

Is it possible to actually boot from NVRAM, ie find a Cisco IOS image there ?

techman-aka-Format

the default reg setting is set to boot to nvram. remember nvram is stored in flash. the nvram holds the starting config. the router will boot to nvran first by default. then there is an order. the order for fallback is flash, tftp server, and then rom. If you're IOS has been blown out for whatever reason the router can boot to a stripped down version of the IOS that is stored in ROM. remember the router will boot to flash by default. but if you change the register setting, you can change the order of the fallback sequence, and change what the router will boot to first.

Hope this helps!!!

good luck!

JSW77

my understanding of this is that if the boot register value (stored in nvram) is set to 2102, then the system looks for INSTRUCTIONS on where to boot from in the config file (nvram). the ios doesnt actually boot from nvram, it just looks for instructions on where to boot from. these instructions are the "boot system flash"etc...commands in the configuration.