Subject: [netmod] YANG 1.1 Issue: YANG Conformance

From: Andy Bierman <[email-masked]>
Date: Mon, 28 Apr 2014 10:12:14 -0700

Hi,

The YANG conformance issues are not listed as part of the YANG 1.1 issue
list.

I would like the YANG Conformance draft added as a WG deliverable to provide
a service-oriented conformance model that allows clients to better
understand
multi-module and partial module conformance requirements.

The current conformance model requires that a server implement
all of the base module if even 1 definition is imported from that module.
Servers do not actually do that, so the current conformance model is
inaccurate
and insufficient for expressing the conformance relationships between
YANG modules.

Solution Proposal:

http://www.ietf.org/id/draft-bierman-netmod-yang-conformance-02.txt

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From: Martin Bjorklund <[email-masked]>
Date: Mon, 28 Apr 2014 21:51:09 +0200 (CEST)

Andy,

I don't understand if you want anything added to the issues list or
not.

Also see Y15 and Y16; they are related.

/martin

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From: Andy Bierman <[email-masked]>
Date: Mon, 28 Apr 2014 13:37:58 -0700

Hi,

Perhaps you should read my email more carefully.
There are 4 problems:

  1) service conformance cannot be specified,
      because it may require multiple YANG modules, or portions
      of specific modules

  2) conformance requirements for new (perhaps external) use-cases
     are not supported, because new if-feature statements cannot be
     added or changed. A use case may require implementation of
     a mandatory=false object, which is not supported in YANG.

  3) A server often does not implement an entire imported module if it just
      needs part of it (e.g. an identity, typedef, ot notification).  The
YANG
      conformance tells the client that the entire base module is supported

  4) advertisement of service-level conformance is not supported

Are you objecting to adopting the YANG Conformance draft as a WG draft?

Andy

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From: Martin Bjorklund <[email-masked]>
Date: Tue, 29 Apr 2014 13:11:31 +0200 (CEST)

> Are you objecting to adopting the YANG Conformance draft as a WG draft?

First of all, I think some issues you have in this draft are handled
by some of the 1.1 issues, e.g., boolean if-feature expressions.

Second, it don't think this document in its current form solves the
problems you mention, since it doesn't change the conformance
requirements of YANG.  A server still must follow the rules of 6020
(or 6020bis) even if your draft is implemented.

I am all for a modular approach; if we agree on a solution with
packages, 6021bis could refer to the other document.

Anyway, I have added a rather generic issue Y45.

/martin

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From: Andy Bierman <[email-masked]>
Date: Tue, 29 Apr 2014 05:19:34 -0700

> by some of the 1.1 issues, e.g., boolean if-feature expressions.
not really, since the original module has to be modified to change
if-feature-stmts,
and it is illegal to add or change if-feature-stmts.  There is no way to
indicate
that for condition X, YANG feature Y MUST be supported.  A set of purely
optional features is not the same as service-level conformance.
SMIv2 is far better than YANG wrt/ conformance specification.

> (or 6020bis) even if your draft is implemented.
yes it does.  You cannot build a routing service given any single standard
YANG module. You need interfaces + routing-cfg + ipv4 | ipv6.
YANG has no way to specify that conformance.

Andy