On Fri, Jan 13, 2017 at 12:51 AM, Juergen Schoenwaelder <
j.schoenwael...@jacobs-university.de> wrote:

> On Thu, Jan 12, 2017 at 02:05:07PM -0800, Andy Bierman wrote:
> >
> > So this thread is questioning why YANG allows constraints on config=false
> > data nodes.
> >
> The point I am trying to make is that for configuration data, we have
> a clear model what validation means and when it is applied. The basic
> idea is that the running configuration of a system is always valid and
> configuration changes will never leave the running configuration in an
> invalid state, i.e., configuration change requests are rejected if
> they would leave to invalid configuration state.
> For operational state data, it is not entirely clear where and when
> validation will occur or if it will occur at all. In fact, if a system
> is in a weird state, it might actually be useful for certain purposes
> to expose the weird state. And, as Martin pointed out, inconsistencies
> may also result from the technical difficulties to take a consistent
> snapshort of a system with several concurrent subsystems. For these
> reasons, the assumption that a server always returns valid operational
> state data is likely not true.
> > From the generic toolbuilder POV, it allows the YANG engine to
> > report issues to the operator without custom programming for each
> > little issue. Who knows why the foo-table requires 3 entries to be
> > valid min-elements 3). The tool can report to the operator
> > "foo-table does not have enough entries" and let the operator decide
> > what to do about it.
> Yes, it will be up to the client's functionality and its implemention
> specifics to deal with the question whether it is useful to validate
> operational state data or what to do if the received operational state
> data is invalid.
> While servers are expected to be strict about the validity of
> configuration data, I think clients need to be lenient about the
> validity of operational state data.

Actually, a client that is not restricted by NACM can use the YANG
validation just fine.
There are opstate tables that churn but that is the exception.

Also note that the rpc/input and action/input constraints are validated
by the server, and MUST be implemented.  The XPath in these contexts
are allowed to reference state data (starting in YANG 1.1)

> /js


> --
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103         <http://www.jacobs-university.de/>
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