[j-nsp] Old JunOS upgrade path

[Tom Beecher]

This was, and still is, the most accurate answer in the thread. To expand
on it further....

Cisco IOS images are standalone binary images. Each time the device is
powered on, it loads the image it is configured too, and executes it. The
entire operating system is encapsulated in this image file, and it's
execution is completely independent of any image is has executed
previously, or will in the future. You don't really 'upgrade' a Cisco IOS
device ; you just tell it to load a different image.

Junos is a complete operating systems. Just like your home computer, each
time the device loads, it is loading the complete OS in the state that it
was when it was shut down. ( Hopefully. :) ) When you upgrade it, the
process only modifies certain components. Any OS upgrade process like that
will have restrictions and dependencies that dictate where you can upgrade
from based on where you are now.  You always have an option to do a clean
install of the version you want, but that is a complete removal and
replacement of the entire OS.

Cisco NX-OS is the same way. I've watched our datacenter guys have to do
the exact same intermediate upgrade, X -> Y -> Z , if the version gap was
large enough that X -> Z was not doable. Exact same reason as JunOS.

On Fri, Mar 8, 2019 at 4:14 PM Gert Doering <gert at greenie.muc.de> wrote:

> Hi,
>
> On Fri, Mar 08, 2019 at 01:17:44PM -0700, Eldon Koyle wrote:
> > Many (most?) network operating systems are an image file that the
> > switch either writes over a partition (ie. block-level copy) or boots
> > directly (ie. initrd/initramfs) with a separate partition for a config
> > file.  Junos is a full BSD operating system that installs packages to
> > partitions on the device, runs upgrade scripts, etc.
>
> So?
>
> gert
> --
> "If was one thing all people took for granted, was conviction that if you
>  feed honest figures into a computer, honest figures come out. Never
> doubted
>  it myself till I met a computer with a sense of humor."
>                              Robert A. Heinlein, The Moon is a Harsh
> Mistress
>
> Gert Doering - Munich, Germany
> gert at greenie.muc.de
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