Re: [netconf] Should a NETCONF server implement YANG Library 1.1 if it does not support NETCONF NMDA?

[Jernej Tuljak <[e-mail]>]

On 01/07/2021 14:25, Andy Bierman wrote:
>
>
> On Thu, Jul 1, 2021 at 1:36 AM Vladimir Vassilev 
> <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>
>     On 30/06/2021 10.33, Jernej Tuljak wrote:
>     > Hi,
>     >
>     > I have a relatively simple question, stated in the subject.
>     >
>     > I cannot find any concrete text that would advise against,
>     prohibit or
>     > encourage such a thing, but is ietf-yang-library@2019-01-04
>     intended
>     > to be used in such a way; to be implemented in a non-NMDA
>     NETCONF server?
>     >
>     > How should a NMDA enabled NETCONF client handle a situation where
>     > :yang-library:1.1 capability is advertised by the NETCONF
>     server, but
>     > ietf-netconf-nmda module is not (assuming that the client is also
>     > capable of acting as a legacy client)?
>
>     IMO all NETCONF servers that implement :yang-library:1.0 implement
>     NMDA
>     where "all datastores have exactly the same schema". Those servers
>     can
>     trivially implement :yang-library:1.1. I am not aware of any formal
>     requirement for such implementation to also implement
>     ietf-netconf-nmda
>     - e.g. <get-data>.
>
>
> Correct.
> If module A does not import or even mention module B,
> then it safe to assume that there is no requirement to implement B
> if A is supported.
>
> It is trivial for the server to support the new YANG library, and at 
> least 2 implementations
> use the same approach even if NMDA is enabled.

I'm more interested in the case where the server does not support NMDA 
but implements YANG Library 1.1. I'd like to see a concrete example of 
the server's <hello> message and content of a response to a client's 
<get> request on /ietf-yang-library:yang-library data tree branch for 
this case.

We have seen different approaches used in the wild and none of them make 
much sense to us. The intention of YANG Library 1.1 seems to be pretty 
clear - to announce NMDA datastore schema compliance. I do not see how 
it can be used in a different context so an example would be appreciated 
greatly.

Jernej

>
> It has never been trivial for a client to support NMDA, and that is 
> why NMDA
> is not being adopted (but the server-centric WG still thinks the jury 
> is out on NMDA).
>
>
>     IMO client software using <get> and <get-config> should not need
>     changes
>     to support device servers upgraded to support :yang-library:1.1
>     with or
>     without implementation of ietf-netconf-nmda (<get-data> etc.).
>
>
> This is not just an opinion.
> No words in RFC 6241 are altered because NMDA is implemented.
> The <get> and <get-config> operations work exactly the same as before 
> NMDA existed.
>
>     /Vladimir
>
>
>
>
> Andy
>
>     >
>     > Jernej
>     >
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