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

Italo Busi <Italo.Busi@huawei.com> Wed, 19 May 2021 18:22 UTC

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From: Italo Busi <Italo.Busi@huawei.com>
To: 'Andy Bierman' <andy@yumaworks.com>
CC: "netmod@ietf.org" <netmod@ietf.org>, "teas@ietf.org" <teas@ietf.org>
Thread-Topic: [netmod] Question about optional data nodes in YANG
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Date: Wed, 19 May 2021 18:22:10 +0000
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Subject: Re: [Teas] [netmod] Question about optional data nodes in YANG
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Then, what would be the difference between an optional and a mandatory data node?

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

Italo

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<mailto: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

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