Re: [netmod] [Netconf] magic leaf 'type' in IETF interfaces

Andy Bierman <andy@yumaworks.com> Thu, 20 December 2018 15:31 UTC

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From: Andy Bierman <andy@yumaworks.com>
Date: Thu, 20 Dec 2018 07:31:43 -0800
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To: "Belotti, Sergio (Nokia - IT/Vimercate)" <sergio.belotti@nokia.com>
Cc: Jan Lindblad <janl@tail-f.com>, "netconf@ietf.org" <netconf@ietf.org>, "netmod@ietf.org" <netmod@ietf.org>
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Subject: Re: [netmod] [Netconf] magic leaf 'type' in IETF interfaces
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On Thu, Dec 20, 2018 at 1:08 AM Belotti, Sergio (Nokia - IT/Vimercate) <
sergio.belotti@nokia.com> wrote:

> Hi,
>
>
>
> On Wed, Dec 19, 2018 at 6:16 AM Ladislav Lhotka <lhotka@nic.cz> wrote:
>
> Jan Lindblad <janl@tail-f.com> writes:
>
> > Hi,
> >>> While I agree with Martin, in our systems we have a number of places,
> where the system does create configuration in running, due to
> >>>
> >>> different levels of automation and autonomous algorithms kick-in
> >>> the created config needs to be possible to be further modified by the
> operator
> >>> the created config needs to be referenced from operator created config
> >>> the created config is not always ephemeral, it might need to be part
> of backup/restore
> >> This is only a sampling from "the list of excuses". I have heard many
> more. The road to hell is paved with good intentions, however.. If we want
> to build automation based on sound theory, clearly separating the orders
> from managers from a system's own operational view is key, IMO.
> Reliability, security, accountability are growing in importance, and they
> all play in this direction.
> >>
> >> We may not need to standardize rules to outlaw the above; the market
> will take care of that. What we need to ensure is that it is possible to be
> standards compliant without having to implement design excuses like these.
> >>
> >>
> >> NMDA has a lot of room for proprietary mechanisms for converting
> <running> to <intended>.
> >> Many times the features desired by engineers exceed the capabilities of
> YANG, such as
> >> a dynamic default leaf.  YANG allows a simple constant, and no business
> logic to pick the default.
> >> This is a very valid use of "server auto-magic".
> >>
> >> Maybe a future version of YANG can improve the client visibility into
> this "auto-magic"
> >
> > As you say, this is not uncommon. I usually recommend to leave out any
> > default statement, and write in the description what happens if this
> > leaf isn't set. The operator can then override the default by giving a
> > value.
>
> Anyway, this is not a case where the server writes something on its own
> to a configuration datastore.
>
>
>
>
>
> I don't think it is a problem if NMDA or non-NMDA servers write to
> <running>.
>
> Just part of the complexity that is baked in -- NMDA does nothing to help
> the client know
>
> why <running> is different than <intended> anyway.
>
>
>
> SB>> But RFC 8342 says :
>
> “It represents the configuration after all configuration transformations
> to <running> are performed (e.g.,template expansion, removal of inactive
> configuration)”
>
>
>
> So my understanding is that by definition “intended” can be different from
> “running”.
>
> Am I missed something?
>
>
>


The client can see WHAT changed because of server-auto-magic but not WHY
a particular server implementation converts <foo> into <bar> if <foo> is
edited.
A client (using plain YANG) cannot predict at all what will happen if <foo>
is edited.

The issue remains: how does a client know that a mandatory leaf is not
actually required in <running>?  I guess vague auto-magic description-text
is good enough


Andy


> >
> > While some more advanced features for default values may be of some
> > utility, the simplicity of YANG is also important. We don't want to
> > make the YANG models -- the interface contracts -- the new place for
> > all business logic.
>
> Absolutely.
>
>
>
> I am not proposing YANG needs a new default-stmt. There is a
> description-stmt
>
> and vendors can add their own extensions to flag auto-magic data nodes.
>
>
>
> Lada
>
> >
> > /jan
>
>
>
>
>
> Andy
>
>
>
> Thanks
>
> Sergio
>
>
>
> Sergio Belotti
>
> Senior System Engineer and Standardization Architect
>
> IP/Optical Networks, Optics BU
>
> Nokia
>
> M: +39-335761776
>
> Via Energy Park, 20871 Vimercate (MB) , Italy
>
> sergio.belotti@nokia.com
>
>
>
>
>
>
>
> >
> > _______________________________________________
> > netmod mailing list
> > netmod@ietf.org
> > https://www.ietf.org/mailman/listinfo/netmod
>
> --
> Ladislav Lhotka
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
>
>