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bootvar
- Thread starter rbelt
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ok... forget bootvar -- it's not needed cause the variables show up in the config file.
What I don't understand is the order of things. The config-register setting tells the system where to boot (the IOS) from (e.g. rom, flash, net, etc.). After the IOS is loaded, it then finds and executes the config file... which is supposed to have the information telling it where to load the IOS! So how can the system find the boot system variables before the IOS is loaded? What happens if nvram is corrupt or startup-config is missing? Also, is it possible to have multiple startup-config files saved on the router, nvram (I don't think so but wanted to check)?
thanks
//RB
What I don't understand is the order of things. The config-register setting tells the system where to boot (the IOS) from (e.g. rom, flash, net, etc.). After the IOS is loaded, it then finds and executes the config file... which is supposed to have the information telling it where to load the IOS! So how can the system find the boot system variables before the IOS is loaded? What happens if nvram is corrupt or startup-config is missing? Also, is it possible to have multiple startup-config files saved on the router, nvram (I don't think so but wanted to check)?
thanks
//RB
ping rbelt
....!
Success rate is 20 percent (1/5), round-trip 26 days
To clarify the cisco2500 default boot sequence:
1. The router will load the first IOS image in flash.
2. The IOS will load and look for the start-up config file stored in the NVRAM.
3. If there is not startup file in NVRAM, it defaults to the initial "setup-mode".
There are other varied boot sequences depending on your IOS status or boot register. You can also modify the boot sequence through the config-register; eg..
0x2100 ROMMON mode
0x2101 boot from ROM (bootstrap mode)
0x2102 boot NVRAM sequence
0x2142 boot to bypass startup file in NVRAM.
ROMMON and bootstrap mode are different. Sometimes people confuse the two.
ROMMON gives you limited commands. The ROMMON prompt is normally rommon> or just >
The bootstrap is a cut down version of and IOS, loaded from the router ROM. The bootstrap prompt is normally Router (boot)>.
When you do a sh version, the router tells you what the config-register is set to, what the IOS file it will load and what the bootstrap file it will load by default.
You can only have one default start-up config in NVRAM. You could save copies of different startup config files in flash and load them manually (ie. copy them as the default start-up config).
Other router models work a little differently. eg.. on a cisco7500, it loads the bootstrap, then the startup file and boots the IOS filename defined in the start-up file.
JimmyZ
....!
Success rate is 20 percent (1/5), round-trip 26 days
To clarify the cisco2500 default boot sequence:
1. The router will load the first IOS image in flash.
2. The IOS will load and look for the start-up config file stored in the NVRAM.
3. If there is not startup file in NVRAM, it defaults to the initial "setup-mode".
There are other varied boot sequences depending on your IOS status or boot register. You can also modify the boot sequence through the config-register; eg..
0x2100 ROMMON mode
0x2101 boot from ROM (bootstrap mode)
0x2102 boot NVRAM sequence
0x2142 boot to bypass startup file in NVRAM.
ROMMON and bootstrap mode are different. Sometimes people confuse the two.
ROMMON gives you limited commands. The ROMMON prompt is normally rommon> or just >
The bootstrap is a cut down version of and IOS, loaded from the router ROM. The bootstrap prompt is normally Router (boot)>.
When you do a sh version, the router tells you what the config-register is set to, what the IOS file it will load and what the bootstrap file it will load by default.
You can only have one default start-up config in NVRAM. You could save copies of different startup config files in flash and load them manually (ie. copy them as the default start-up config).
Other router models work a little differently. eg.. on a cisco7500, it loads the bootstrap, then the startup file and boots the IOS filename defined in the start-up file.
JimmyZ
- Thread starter
- #6
the ping parody was quite funny!
Thanks for the rundown of the boot basics but it seems to be missing an important part -- or rather, I'm quite confused over boot system.
The 'boot system' variable is used to specify the system image that the router loads at startup. Boot system is linked to config-register but I'm not 100% sure of the relation however, i think that if I set the config-register to 0x2102 and add to the startup-config:
boot system tftp (location1)
boot system tftp (location2)
boot system flash:...
boot system rom
then the system will first try the tftp server (location1) then (location2), then the referenced flash file and finally rom... at least that's how I understand it.
What I really don't get is that the boos system variables are stored in the startup-config which is loaded AFTER the system image, so how does the router know where to get the system image from? See my confusion?
thanks much!
//RB
Thanks for the rundown of the boot basics but it seems to be missing an important part -- or rather, I'm quite confused over boot system.
The 'boot system' variable is used to specify the system image that the router loads at startup. Boot system is linked to config-register but I'm not 100% sure of the relation however, i think that if I set the config-register to 0x2102 and add to the startup-config:
boot system tftp (location1)
boot system tftp (location2)
boot system flash:...
boot system rom
then the system will first try the tftp server (location1) then (location2), then the referenced flash file and finally rom... at least that's how I understand it.
What I really don't get is that the boos system variables are stored in the startup-config which is loaded AFTER the system image, so how does the router know where to get the system image from? See my confusion?
thanks much!
//RB
rbelt,
The boot sequence can vary slightly depending on the model of router. Some of the higher-end router (ie. 7500) will follow your boot system method. They load a basic bootstrap first, read the startup file and then boot the system file listed in the startup file. For a 2500, the router follows the method I mention. There are many different config-register settings which can change the default boot sequence. You could try playing around with different scenarios, on a spare router to cure your curiosity. Then you could post your findings on the forum.
JimmyZ
The boot sequence can vary slightly depending on the model of router. Some of the higher-end router (ie. 7500) will follow your boot system method. They load a basic bootstrap first, read the startup file and then boot the system file listed in the startup file. For a 2500, the router follows the method I mention. There are many different config-register settings which can change the default boot sequence. You could try playing around with different scenarios, on a spare router to cure your curiosity. Then you could post your findings on the forum.
JimmyZ
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