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I had to downgrade a couple of Cisco 3925 routers last week and one of the steps in the instructions (link provided) was to change the boot command that was given by the following command:

Cisco-3925# show run | include boot

The downgrade went fine, but what I'd like to know is why this command didn't show any boot instruction before the downgrade was successful. Here is the output of that command:

boot-start-marker
boot-end-marker

How did the router boot before the downgrade in the first place?

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up vote 3 down vote accepted

If you have no boot command specified, by default the router loads the first IOS image that it finds in flash, alphanumerically. If you have 2 IOS images on your flash drive the rooter will boot the oldest IOS version that it finds (typically).

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Why does it use the older one? –  paradroid May 12 '12 at 0:03
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It goes in alphabetical then numerical order. So if you have 12.1.0 and 12.1.1 on the drive it will use the older 12.1.0 image. –  resmon6 May 14 '12 at 17:54
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