Re: [netmod] Clarifications re RFC 8342 NMDA

Schönwälder, Jürgen <J.Schoenwaelder@jacobs-university.de> Fri, 03 January 2020 15:43 UTC

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From: =?iso-8859-1?Q?Sch=F6nw=E4lder=2C_J=FCrgen?= <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: Fri, 3 Jan 2020 15:43:31 +0000
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Subject: Re: [netmod] Clarifications re RFC 8342 NMDA
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On Fri, Jan 03, 2020 at 11:39:31AM +0000, Jonathan wrote:
> > 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 6241 describes <get> as retrieving "running configuration and device
> state information" and <get-config> as retrieving "all or part of a
> specified configuration datastore". RFC 8526 introduces <get-data> which it
> describes as "similar to NETCONF's <get-config> operation". As far as I can
> tell, neither RFC 8342 not RFC 8526 actually identify which operation to use
> to retrieve operational state data. Am I right in assuming it would be
> <get-config>? In that case, it is similar to <get> when performed on
> <operational> as it will also return state data.

There is quite some discussion of 'operational state datastore' in
subsections of section 3.1.1 'The <get-data> Operation' in RFC 8526.
There is also an example in section 3.1.1.4.

The <get-config> operation returns config data, hence it won't return
config false data, i.e., its not a good choice for <operational>. The
reason why we have NMDA is that <get> semantics have been found to be
problematic. Hence, NMDA systems should use RFC 8526 operations
(<get-data> and <edit-data>) when talking to each other.

> And what should be the result of performing <get> on an NMDA-supporting
> server? Should it still return config true nodes from <running> plus config
> false nodes from <operational>? Or should the operation be rejected?

A proper NMDA client should never send a <get>. Supporting <get> only
makes sense for legacy clients and they might expect RFC 6241
behaviour as far as that is implementable (the reason we have NMDA is
that <get> semantics assume that <running> is identical to <applied>
config, which is just not always true).

/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/>