From: netmod <[email protected]<mailto:[email protected]>> on
behalf of Mahesh Jethanandani
<[email protected]<mailto:[email protected]>>
Date: Wednesday, July 27, 2016 at 9:07 PM
To: Xufeng Liu <[email protected]<mailto:[email protected]>>
Cc: netmod WG <[email protected]<mailto:[email protected]>>
Subject: Re: [netmod] OpsState Direction Impact on Recommended IETF YANG Model
Structure
Robert mentions IS-IS, and if I look at OSPF, I see a clear separation of rw
and ro nodes.
Right - and this separation is based on the routing and routing-state split in
the ietf-routing-cfg model. In general, ietf-routing-cfg specifies that all
control plane protocol YANG models should adapt this structure. Anyone who
thinks collapsing all the models one config/state tree is simply a matter of
moving a few counters should taking a better look at the existing drafts. I
outlined the options in the E-mail thread prior to IETF 96. Now, with the
context of IETF 96 behind us, I believe more NETMOD participants will
understand the options. To review the options specified in the previous E-mail
thread.
1. Do nothing - allow them proceed as they are with multiple ways of
representing the applied configuration. This would provide visibility to
the data independent of whether or not the device supported the revised
data-stores supporting implicit retrieval of the applied configuration.
2. Prune out the redundant data nodes except those required as list
keys, etc, since they can be obtained from the applied state data store.
3. #2 plus collapse the config (read-write) and system-state
(read-only) into common containers. No more branching of
<model-name>-config and <model-name>-state at the top level of the model.
Prior to IETF 96, I don’t believe we had selected a direction. However, I
believe we agreed on option #1 in order to allow the publication of these
models within the next year. We’d still be able to avail the benefits of
applied vs intended configuration on network devices supporting these data
stores.
Thanks,
Acee
On Jul 27, 2016, at 11:22 AM, Xufeng Liu
<[email protected]<mailto:[email protected]>> 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:[email protected]] On Behalf Of Robert Wilton
Sent: Wednesday, July 27, 2016 1:05 PM
To: Kent Watsen <[email protected]<mailto:[email protected]>>; netmod WG
<[email protected]<mailto:[email protected]>>
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
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