Re: [netmod] Clarifications re RFC 8342 NMDA

Schönwälder, Jürgen <J.Schoenwaelder@jacobs-university.de> Thu, 02 January 2020 18:37 UTC

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From: "Schönwälder, Jürgen" <J.Schoenwaelder@jacobs-university.de>
To: Jonathan <jonathan@hansfords.net>
CC: "netmod@ietf.org" <netmod@ietf.org>
Thread-Topic: [netmod] Clarifications re RFC 8342 NMDA
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Date: Thu, 02 Jan 2020 18:37:06 +0000
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Subject: Re: [netmod] Clarifications re RFC 8342 NMDA
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On Thu, Jan 02, 2020 at 05:12:30PM +0000, Jonathan wrote:
> Hi,
> 
> I have been reading through RFC 8342 and have a number of questions I
> couldn't resolve after a couple of passes through. Can anyone advise?
> The RFC states "The startup configuration datastore may not be supported by
> all protocols or implementations", "the candidate configuration datastore
> may not be supported by all protocols or implementations" and "<running>
> MUST be supported if the device can be configured via conventional
> configuration datastores". I can find no explicit guidance on:The intended
> configuration datastore: The RFC does state, "Whenever data is written to
> <running>, the server MUST also immediately update and validate <intended>."
> Is <intended> mandatory for NMDA-supporting servers that support
> <running>?

It is not mandatory to expose <intended>. On simple implementations,
<intended> may be identical with <running>.

> The operational state datastore: The RFC does state it is "a
> read-only datastore that consists of all "config true" and "config false"
> nodes defined in the datastore's schema" and that "the datastore schema for
> <operational> MUST be a superset of the combined datastore schema used in
> all configuration datastores ...". Is <operational> mandatory for
> NMDA-supporting servers?

Since <operational> is the only way to expose config false nodes for
an NMDA server, it is kind of mandatory as soon as you have config
false nodes to expose.

> RFC 8525, section 1 states, "For backwards
> compatibility, an NMDA-supporting server SHOULD populate the deprecated
> "/modules-state" tree in a backwards-compatible manner."That suggests an
> NMDA-supporting server SHOULD be backwards-compatible with a
> non-NMDA-supporting client. Is that correct?

This might be a misuse of 'SHOULD' since backwards-compatibility is
important for a transition phase but not in pure NMDA environments.
The idea here was to encourage support for a transition phase where
NMDA and non-NMDA implementations may need to co-exist.

> Can an MMDA-supporting client be
> backwards-compatible with a non-NMDA-supporting server?

An NMDA client should talk NMDA with an NMDA server. Whether an NMDA
client also talks to non-NMDA servers is up to the implementor. I
personally would distinguish between the protocol interaction and the
data model of the management application. To me, it makes a lot of
sense to make the data model of the management application NMDA aware
even if the application is used with non-NMDA servers.

> I can't find any
> mention of YANG version 1 in RFC 8342. Is it safe to assume NMDA is
> compatible with YANG version 1 modules?

It should not matter whether the model is written in YANG 1 or 1.1.
However, core data models are moving towards YANG 1.1.

/js

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