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Did you know that you can configure your router to boot another IOS if the flash is corrupted? Well,
you can. In fact, you just might want all your routers to boot from a TFTP host each time anyway
because that way, you’ll never have to upgrade each router individually. This may be a smooth way
to go because it allows you to just change one file on a TFTP host to perform an upgrade.
There are some boot commands you can play with that will help you manage the way
your router boots the Cisco IOS—but remember, we’re talking about the router’s IOS here,
not the router’s configuration!
Router>en
Router#config t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#boot ?
bootstrap Bootstrap image file
config Configuration file
host Router-specific config file
network Network-wide config file
system System image file
274 Chapter 5 Managing a Cisco Internetwork
The boot command truly gives you a wealth of options, but first, I’ll show you the typical
settings that Cisco recommends. So let’s get started—the boot system command will allow
you to tell the router which file to boot from flash memory. Remember that the router, by
default, boots the first file found in flash. You can change that with the following commands:
Router(config)#boot system ?
WORD TFTP filename or URL
flash Boot from flash memory
ftp Boot from a server via ftp
mop Boot from a Decnet MOP server
rcp Boot from a server via rcp
rom Boot from rom
tftp Boot from a tftp server
Router(config)#boot system flash c2800nm-advsecurityk9-mz.124-12.bin
The above command configures the router to boot the IOS listed in it. This is a helpful command
for when you load a new IOS into flash and want to test it, or even when you want to totally
change which IOS is loading by default.
The next command is considered a fall-back routine, but as I said, you can make it a permanent
way to have your routers boot from a TFTP host. Personally, I wouldn’t necessarily
recommend doing this (single point of failure); I’m just showing you that it’s possible:
Router(config)#boot system tftp ?
WORD System image filename
Router(config)#boot system tftp c2800nm-advsecurityk9-mz.124-12.bin ?
Hostname or A.B.C.D Address from which to download the file
<cr>
Router(config)#boot system tftp c2800nm-advsecurityk9-mz.124-12.bin 1.1.1.2
Router(config)#
As your last recommended fall-back option—the one to go to if the IOS in flash doesn’t
load and the TFTP host does not produce the IOS—load the mini-IOS from ROM like this:
Router(config)#boot system rom
Router(config)#do show run | include boot system
boot system flash c2800nm-advsecurityk9-mz.124-12.bin
boot system tftp c2800nm-advsecurityk9-mz.124-12.bin 1.1.1.2
boot system rom
Router(config)#
To sum this up, we now have Cisco’s suggested IOS backup routine configured on our
router: flash, TFTP host, ROM.