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BOOT SYSTEM COMMANDS

mikey250
mikey250 asked
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Hi,

Qns1. If an IOS has been added already and boots up as normal then why use 'Boot System' commands?

Qns2.  Why have I seen in some cases 2 'Boot System' commands on a switch for eg ?
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Consulting and Network/Security Specialist
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Commented:
If there are no definitions which IOS is supposed to be booted, IOS will sequentially try the present images. If booting one IOS fails, it will attempt to boot the next IOS and so on.

1) in order to prevent the system from booting the "wrong" IOS if additional IOS images are present

2) to limit the IOS images booted in case there are yet more images, as well as ensure the desired sequence at which IOS images are booted.

Author

Commented:
Hi yes I basically realised that but thanks for your comments:

Qns1. Does 'boot system' command take priority over normal boot process?
Qns2. Im assuming all IOS's are located in same place so if in the event there are 2 'boot system' commands then if the first specified is not located for I suppose corruption or whatever then it will jump to the next - ?

Qns3.  Are 'boot system' a must in any environment as obviously if a network goes down it has the ability to reboot and presumably at least give some form of network continuity - ?

Qns4. I may have been mistaken where I saw the 'boot system' command as it may have been a 2811 router!
Garry GlendownConsulting and Network/Security Specialist
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Commented:
1 Yes - if the image referenced in the boot system command does not exist, booting will fail, without fallback to any other image.

2 yes. Though the sources might be different, e.g. system flash, USB, etc ...

3 Personally, I prefer not to network-boot for exactly that reason. But they are not really necessary, if you have an image locally, it will automatically be used.

The boot system command should be available on just about every current Cisco platform using IOS...

Author

Commented:
Qns1. Oh ok so 'boot system' command does take precedence over the normal boot process when detecting the IOS in flash, but if the 'boot system' command fails, you say it will not fall back to any other image in the IOS whether it is there or not ?

Ive seen boot system commands being used at one place I used to work but what it down to preference..The users I spoke to said it was for resilence ie backup..
Garry GlendownConsulting and Network/Security Specialist
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Commented:
Correct. With boot system, there's no fallback to loading just any IOS image.

Author

Commented:
But there is a fall back with not using a 'boot system' command, as normal is if the flash not detected it eventually ends up at ROM mode.

So the only useful thing with using 'boot system' commands that I can see is if 2 are used rather than 1 as you say no fallback..
Garry GlendownConsulting and Network/Security Specialist
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Commented:
Correct. Or - as mentioned - if you want to ensure the sequence of images loaded.

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