Re: [YANG] mandatory & default

"Randy Presuhn" writes:
>One of the reasons for archiving configurations
>is so that if a box fails, a replacement can be quickly made
>to function in its place.

Loading the saved file with defaults won't make this
any saner, safer, or stronger.  It increases the fragility,
but incorporating into the saved file tons of stuff about
which you don't care.  It something fails on these values
that you don't care about, you are broken.

>If there is even a remote chance
>that a default value might change between releases or on
>different versions of a hardware platform, that value needs
>to be included in an archive of the configuration.

The chance of a change in defaults (which annoy customers to
no end) is minor compared to the change of adding features (which
customers insist on) and the need to support downgrading (which
customers insist on).

Consider this example from JUNOS-land.  We have a set of foo-options
containers that are used to hold media-specific options under
the [interfaces] statement.  These options are numerous, verbose,
and rarely used.  If I add a new statement in release 9.0 and
start emitting a boring default value for it, I can no longer
load that config in any release predating 9.0.

In avoiding a rare bug (changing defaults), you'll break real
operational usage.

Thanks,
 Phil

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