Re: [netmod] Y60 - coexistence with YANG 1.0

[Ladislav Lhotka <[e-mail]>]

> On 10 Sep 2015, at 13:45, Martin Bjorklund <[e-mail]> wrote:
> 
> Ladislav Lhotka <[e-mail]> wrote:
>> 
>>> On 10 Sep 2015, at 12:55, Martin Bjorklund <[e-mail]> wrote:
>>> 
>>> Hi,
>>> 
>>> I think we agreed that is ok for a YANG 1.1 module to import a YANG
>>> 1.0 module.
>>> 
>>> But should it also be ok for a 1.0 module to import a 1.1 module?
>> 
>> I think it should be illegal for a 1.0 module to import with revision
>> if the requested revision is 1.1.
> 
> Ok.
> 
>>> If we make this illegal, we might run into problems.  For example,
>>> ietf-ip imports ietf-interfaces.  Suppose we update ietf-interfaces
>>> and the new version use YANG 1.1.  Is it ok for a server to implement
>>> the 1.0 version of ietf-ip and 1.1 version of ietf-interfaces?  If the
>>> answer is no, it means that we either have to update all modules to
>>> 1.1 more or less at the same time (including vendor models!), or we
>>> keep existing modules on 1.0 "forever".
>>> 
>>> At the lastest interim, it was suggested that a server that implements
>>> such a combination of models would internally promote the 1.0 module
>>> to 1.1, and thus make this combination legal.
>> 
>> I think we need a way for the server to identify itself to the client
>> as 1.1-capable, and then:
>> 
>> - 1.1-capable server: if 1.0 module X imports Y *without revision*, and
>>  the revision of Y advertised by the server (with
>>  default-revision=true), then module X is automatically interpreted as
>>  1.1.
> 
> I assume you mean that Y is 1.1.

Yup.

> 
>> - 1.0-only server: if 1.0 module X import Y without revision, then the
>>  latest 1.0 revision of Y is used. If 1.1 revisions exist, they are not
>>  used.
> 
> Yes.
> 
>>> Such a strategy should also be safe for old clients, still treating
>>> the module as being 1.0.
>> 
>> I am not sure about this, I think a 1.0-only client cannot work with a
>> 1.1-capable server is some 1.1 additions are used (e.g. if-feature
>> expressions).
> 
> Note that the 1.0 client worked with the 1.0 server with 1.0 modules X
> and Y before.  Now Y is updated to 1.1.  According to section 10, Y is
> not allowed to add if-feature to existing definitions.

New (non-mandatory) nodes may be added to Y that use if-feature expressions, new XPath functions etc., and the old client can actually receive instances of these nodes in the configuration.

Lada

> 
> 
> /martin
> 
> 
>>> It is a bit unclear what the server should do if the 1.0 module that
>>> it "internally promotes" to 1.1 contains something that is illegal in
>>> 1.1, e.g.:
>>> 
>>>       default "a\xb”;
>> 
>> We should write an erratum to 6020 making this illegal in 1.0, too.
>> 
>> Lada
>> 
>>> 
>>> Comments?
>>> 
>>> 
>>> /martin
>>> 
>>> _______________________________________________
>>> netmod mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/netmod
>> 
>> --
>> Ladislav Lhotka, CZ.NIC Labs
>> PGP Key ID: E74E8C0C

--
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C