Re: [netmod] Questions about how to assign default values with YANG

[Italo Busi <[e-mail]>]

Thanks again Juergen,

This was really helpful

I still have one doubt:

> > Does it mean that a server may not use/implement in the operational
> datastore a leaf for which a YANG default statement has been defined?
> >
> 
> RFC 7950 section 7.6.1 mentions describes situations where a leaf is
> conditional, i.e., there is when condition or an if-feature expression or the leaf
> is a case node.
>

What about the case the leaf is not conditional (but still mandatory false since a YANG default statement is defined)?

May the server still decide not to use/implement this leaf in the operational datastore?

For example, in appendix C.1 of RFC8342, auto-negotiation is enabled by default.
What should be the behavior of a system which does not implement auto-negotiation?
Return the value false or no value (in the operational datastore)?

Italo

> -----Original Message-----
> From: Juergen Schoenwaelder [mailto:[e-mail]]
> Sent: mercoledì 20 gennaio 2021 12:45
> To: Italo Busi <[e-mail]>
> Cc: '[e-mail]' <[e-mail]>
> Subject: Re: [netmod] Questions about how to assign default values with
> YANG
> 
> On Wed, Jan 20, 2021 at 10:51:09AM +0000, Italo Busi wrote:
> >
> > Does it mean that a server may not use/implement in the operational
> datastore a leaf for which a YANG default statement has been defined?
> >
> 
> RFC 7950 section 7.6.1 mentions describes situations where a leaf is
> conditional, i.e., there is when condition or an if-feature expression or the leaf
> is a case node.
> 
> > What would be the value of defining a YANG default statement for  config
> false leaf?
> >
> 
> Technically, this can happen because a type has a defined default value and
> this type may be used by config false leafs.
> 
> An example is the zero-based-counter32 typedef in RFC 6991. However, this
> style may be debated since it (mis)uses a default statement to define an initial
> value. I am not sure whether the pattern of using default statements for
> specifying intial values is a good one.
> 
> /js
> 
> --
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   [phone]         <https://www.jacobs-university.de/>