Re: [Teas] [netmod] Question about optional data nodes in YANG

On Wed, May 19, 2021 at 11:22 AM Italo Busi <Italo.Busi@huawei.com> wrote:

> Then, what would be the difference between an optional and a mandatory
> data node?
>
>
>

Do not confuse "mandatory to implement" with "mandatory that a node be
present".

Mandatory to implement is easy:  If there is an if-feature conditional that
is applied to
a node or one of its ancestors, then it is optional to implement. Otherwise
it is mandatory to implement.

> In some RFC8795 implementations, the support or not support of a data node
> may also depend on the specific network-type so in this case the data node
> cannot be marked as not-supported
>
>
>

This is a different issue.
Server capabilities specific to a data model should be handled in a related
module.

Italo
>
>
>

Andy

> *From:* Andy Bierman [mailto:andy@yumaworks.com]
> *Sent:* mercoledì 19 maggio 2021 19:35
> *To:* Italo Busi <Italo.Busi@huawei.com>
> *Cc:* netmod@ietf.org; teas@ietf.org
> *Subject:* Re: [netmod] Question about optional data nodes in YANG
>
>
>
>
>
>
>
> On Wed, May 19, 2021 at 10:12 AM Italo Busi <Italo.Busi@huawei.com> wrote:
>
> We have got a question about how to deal with YANG optional data nodes and
> in particular how can a client know which optional data node has been
> implemented by a server.
>
>
>
> We think that there is no issue with config=false data nodes. When the
> client retrieves a YANG tree from the operational datastore it will not get
> the data nodes that are not implemented by the server, as reported in
> section 5.3 of RFC8342:
>
>
>
> If no value is returned for a given node, then
>
> this implies that the node is not used by the device.
>
>
>
> Is our understanding correct?
>
>
>
>
>
>
>
> The server is expected to advertise a deviation for not-supported for
> every subtree
>
> it does not implement.
>
>
>
> https://datatracker.ietf.org/doc/html/rfc7950#section-7.20.3.2
>
>
>
>
>
>        deviation /base:system/base:daytime {
>
>          deviate not-supported;
>
>        }
>
>
>
>
>
> Andy
>
>
>
>
>
>
>
> The doubt we have is about the config=true data nodes.
>
>
>
> How can the client know whether the server supports the configuration of
> an optional config=true data node before trying to configure them and
> getting an error message?
>
>
>
> We understand that it is possible to know whether a YANG model or a
> feature of the YANG model (i.e. a group of data nodes) is supported by the
> server. The question is rather on specific data nodes with config=true.
>
>
>
> We have found scenarios where it could be useful to implement a sub-set of
> optional data nodes (profile) of an IETF standard YANG model, but it is not
> very clear how a client can understand which profile has been implemented
> by the server.
>
>
>
> Some examples of profiles of an IETF standard YANG model are provided in:
>
>
>
> https://datatracker.ietf.org/doc/html/draft-busi-teas-te-topology-profiles
>
>
>
> Thanks, Aihua and Italo
>
>
>
> _______________________________________________
> netmod mailing list
> netmod@ietf.org
> https://www.ietf.org/mailman/listinfo/netmod
>
>