Re: [YANG] mandatory & default

On Mon, Jan 28, 2008 at 10:02:13AM +0100, Ladislav Lhotka wrote:
> Juergen Schoenwaelder p????e v Po 28. 01. 2008 v 09:46 +0100:
> > On Sun, Jan 27, 2008 at 08:54:51PM -0800, Randy Presuhn wrote:
> >  
> > > If I'm archiving a configuration, I want to know *exactly*
> > > what it is.  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.   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.
> > 
> > If your replacement is using the exact same hardware configuration and
> > the exact same firmware version, you do not need to worry about the
> > defaults.
> > 
> > If your replacement is not using the exact same hardware configuration
> > and the exact same firmware version, there is a chance that things
> > won't work as expected, with and without saved defaults.
> > 
> > If things fail, you need to have a human to figure out what is the
> 
> Here is the problem with changed defaults: things will not fail, they
> will just work differently from what you expect.

Well, applying a default from an old firmware release to a newer
hardware firmware combination can as well lead to something that does
not fail but work differently from what you expect.

My point is you need to be able to (a) get all configuration settings
of a box and (b) the subset that was explicitely configured. It is
then the operator's choice what to use where and when. Trying to rule
out (a) over (b) or (b) over (a) is wasting time and bandwidth.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1, 28759 Bremen, Germany
Fax:   +49 421 200 3103         <http://www.jacobs-university.de/>

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