Re: [netmod] OpsState Direction Impact on Recommended IETF YANG Model Structure

[Robert Wilton <[e-mail]>]

Hi Xufeng,

OK, so perhaps there is even less consistency in the IETF models than I 
thought!

But actually what I am most interested in (from you and others reading 
the Netmod WG alias), is whether you have an opinion on which direction 
we should go.  Even hearing that you don't have an opinion at all is 
useful input :-)

Thanks,
Rob


On 27/07/2016 19:22, Xufeng Liu wrote:
>
> The assumption of “I suspect that all the routing models will be 
> structured similarly” is not correct. Very few models in routing area 
> structure this way.
>
> Regards,
>
> - Xufeng
>
> *From:*netmod [mailto:[e-mail]] *On Behalf Of *Robert 
> Wilton
> *Sent:* Wednesday, July 27, 2016 1:05 PM
> *To:* Kent Watsen <[e-mail]>; netmod WG <[e-mail]>
> *Subject:* Re: [netmod] OpsState Direction Impact on Recommended IETF 
> YANG Model Structure
>
> On 26/07/2016 21:36, Kent Watsen wrote:
>
>     <Rob Wilton writes>
>
>
>     So my thinking is that if we can't merge "foo-state" into "foo"
>     then instead we should have consistent rules that explicitly state
>     that for all IETF models "foo" and "foo-state" are separate trees
>     with a consistent naming convention and structure.  That should
>     hopefully allow tooling to programmatically relate the two
>     separate trees together.  It may give a path to allow "foo-state"
>     to be merged into "foo" in future, but once IETF has standardized
>     600+ models with separate sub-trees, I cannot see that they would
>     get merged back together again.
>
>     What other alternatives are available?  As a WG we need to tell
>     the other WGs how the IETF YANG models should be structured.
>
>     In short, unfortunately I think that we have probably already
>     missed the opportunity to merge "foo" and "foo-state" subtrees
>     together ...
>
>
>     </Rob Wilton>
>
>     Firstly, I’m trying to get a sense of how big a problem this
>     foo/foo-state thing is. [Note: by foo-state, I’m only referring to
>     counters, not opstate].
>
> RW:
> By counters, I think that we also mean any config false nodes that 
> don't directly represent "applied configuration", right?  E.g. is an 
> interface operationally up or down.
>
>
>        I know about RFC 7223, which was done out of consideration for
>     system-generated interfaces, but how many other such models are
>     there envisioned to be?
>
> RW:
> - Any models that augment RFC 7223 and have config false nodes will be 
> impacted.
> - I thought that quite a lot of other IETF models that are in the 
> process of being standardized have a top level split between "foo" and 
> "foo-state".  E.g the ISIS model (draft-ietf-isis-yang-isis-cfg-08) 
> has this split.  I suspect that all the routing models will be 
> structured similarly.
> - Although it is perhaps worth pointing out that I think that the 
> OpenConfig modules effectively have exactly this same issue (e.g. they 
> have a combined interfaces tree keyed by config true leaves), and they 
> pragmatically just ignore the issue of system created interface entries.
>
>
>      Is this issue currently blocking models from progressing, or are
>     we getting ourselves wrapped around a hypothetical?
>
> RW:
> I think that it is blocking models from progressing.
>
> The current guidance for "intended vs applied" is clear. I.e. there 
> must not be "config false" leaves in the IETF YANG data models to 
> represent "applied config".
>
> But there is no clear guidance for the rest of operational state that 
> isn't applied config.  The other WGs need clear guidance (effectively 
> now) to ensure that they can start publishing models as RFCs.
>
>
>
>       If RFC 7223 is an outlier, then we can address it as a special
>     case (perhaps via the related-state/related-config YANG
>     annotations).  What do you think?
>
> RW:
> Personally, I would like one common convention that applies to all 
> IETF YANG models.
>
> Idealistically I would like foo and foo-state to be merged because I 
> think that will make the models easier to use and maintain in the long 
> term, but I don't know if we are just too late to go in that 
> direction.  It seems to me that the NETMOD WG really should try to 
> come to a decision quite quickly on this, but I don't know how to 
> encourage that.  A virtual interim on just this topic perhaps?
>
>
>     Next, regarding paths forward (assuming 7223 is not an outlier),
>     I’m thinking the opposite.  I’m quite sure that we would never
>     merge the 600+ models with separate subtrees back together again. 
>     So I’m thinking we immediately merge foo and foo-state in all
>     active YANG models (so that the YANG “conceptual” models are
>     stable and good) *and* then we use your idea to programmatically
>     generate the “foo-state” tree, presumably only when needed.  This
>     foo-state tree could be generated offline by tools and provided as
>     a second YANG module in drafts.  In this way, servers (opstate
>     aware or not) can advertise if clients can access the foo-state
>     tree (an opstate-aware server may still advertise it for business
>     reasons, and it can ‘deprecate’ the tree when no longer needed).  
>     We could do the same without tools today by just using a feature
>     statement on, for instance, the interfaces-state container, but I
>     like pushing for tooling upfront so that we’re guaranteed
>     mergeability later.  Thoughts?
>
> RW:
> So the generated "foo-state" tree would contain a copy of all config 
> false nodes in the YANG schema and a "config false copy" of any config 
> true nodes in the YANG schema that are required to provide parental 
> structure for the descendant config false nodes.
> - The Xpath expressions would also need to be adjusted, and possibly 
> some of those might break (or need to be fixed by hand).
> - Groupings might be a problem, but potentially they could be expanded.
>
> Technically this solution might work, but is it possible to get 
> everyone to agree that this is the right direction to go in before we 
> spend time on this?
>
> Thanks,
> Rob
>
>
>
>     Kent // as a contributor
>
>