| Author |
Valid IOS search sequence
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| Wavy Davy 2001-08-31, 8:29 pm |
| Got a question that is bugging me.... Please help!!!
After the POSTs are finished, which order does the router search for a valid IOS image?
I thought the answer was ROM->FLASH->TFTP but one of my resorces states FLASH->TFTP->ROM.
Can somebody please clarify with an explanation?
Thanx,
Wavy | |
| The Ghost 2001-09-01, 1:22 am |
| it all depends on the boot field in the config register.
If the boot field is
0x0 = it runs rom moniter
0x1 = IOS in the ROM
0x2 = NVRAM | |
| Retired-Mod 2001-09-01, 5:20 am |
| The conf-reg bits tell it where to look first not the sequence.
Unless directed in config-reg, it does not look to the ROM first and you wouldn't want it to do that because that is a bare bones OS. You want it to look to flash first and ROM last in normal operations.
Retired | |
| bencher 2001-09-01, 5:52 am |
| 0x2102 is default value. Then the router will load the IOS image from flash or whatever is specified by the boot command in the startup configuration file.
The value of the configuration register can be seen by using the show version command. | |
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| bencher 2001-09-01, 7:07 am |
| So, if the default value is used in the configuration register and their are no boot system commands, the sequence is Flash, TFTP, ROM. | |
| sallama18 2001-09-01, 7:37 am |
| 1-flash
2-tftp server
3-rom
correct order if default register value used. | |
| doctorcisco 2001-09-02, 12:20 am |
| quote:
Originally posted by sallama18
1-flash
2-tftp server
3-rom
correct order if default register value used.
Unless, of course, you change it with:
Router(config)# boot system [source] [filename]
You can put multiple instances of this command in your config; the router will try them in order until one of them succeeds or it runs out of choices. This allows you to specify what to try next if your primary IOS is not available (flash goes bad, aborted IOS upload leaves you with nothing usable in flash, tftp server goes down, etc.)
It might also be worth noting that when there are multiple IOS files in flash, the router will default to the first one.
FWIW,
doctorcisco | |
| Wavy Davy 2001-09-02, 6:44 pm |
| Thank you for all the invaluable input!!!
Cheers,
Wavy | |
| darthfeces 2001-09-06, 8:21 pm |
| bit number
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
default value
0x2102 = binary
0010.0001.0000.0010
0-3 determines boot option
flash = 010
rom = 000
4 = reserved
5 = res
6 = 0 boot nvram 1 = ignore
7 = ios banner 0 = no 1 = yes
8 = enter rommon without power cycling router
9 = res
10 = set a broadcast address
11-12 console port
00 = 9600
01 = 4800
10 = 2400
11 = 1200
13 = boot from rom
14 = works with 10 broadcast
15 = enable diagnostics and ignore nvram |
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