Re: [netmod] revising RFC8366 -- Re: [Anima] BRSKI-AE enum issue -> empty, but what's he encoding ?

[Juergen Schoenwaelder <[e-mail]>]

On Mon, Jun 28, 2021 at 11:54:04AM +0000, tom petch wrote:

[...]

> As you say, this is never going to be an Erratum.

Yep.
 
> A leaf of type empty is encoded as, well, empty.
> <voucher-type/>
> as per RFC 7950.
> 
> When this concept was first mentioned, my sense was that while it was technically possible, it would still add complexity for little gain.  As I see YANG Doctors for ever saying, identity can be augmented, enumeration can not so enumeration are used when you positively want to stop people augmenting, when the concept does not make sense so a revised enum may make sense or a change to something like identity which I see as as big a change as the use of 'empty' but the latter is not in current use and so may cause some uncertainty, some confusion.
>

Enumerations are centrally managed. Section 11 of RFC 7950 does allow
additions to enums but only where the enum itself is defined, i.e.,
you need to create a new revision of the YANG module to add an enum
value. An identity is more flexible as the value space is not
centrally managed.

Using leafs of type <empty/> as a way to define a non-centrally
managed enumerated set of values really is a hack. It may work if
people follow certain rules, but it is unlikely that tools will
understand the rules (i.e., which places of a data model were designed
to be used as a 'leafs of type <empty/> enumeration'). Hence, there is
nothing that will prevents people from augmenting in a leaf that is
not using the type empty or even an entire subtree of YANG definitions.

I do not know exactly what the issue with RFC 8366 is but it seems you
will have to revise the YANG module defined in RFC 8366 anyway.

Note that there is also a middle ground, namely an enumeration type
factored out into an IANA maintained module that is process wise
easier to extend - should extensions be needed more regularly.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
Fax:   [phone]         <https://www.jacobs-university.de/>