[Teas] Question about optional data nodes in YANG

[Italo Busi <[e-mail]>]

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 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