Dear all,
Focusing on draft-wu-l3sm-rfc8049bis, the big problem is: RFC8049 is
broken. The small problem is: trying to maintain backward compatibility.
draft-wu-l3sm-rfc8049bis has rightly focused on the big problem.
Let me extend the scope of this email thread from "handling module
incompatibility" to "handling module incompatibility and NMDA transition".
As I mentioned in the past (see "semver.org comparison of two YANG
modules" email in NETMOD), I believe the IETF will have to change its
way of working in terms of backward compatibility. See also the email
"ietf-routing or ietf-routing-2? module naming convention for NMDA
transition. Re: [netmod] upcoming adoptions" in NETMOD.
However, we will have to tackle this discussion one day or the other:
- we need _an automatic way_ to make the link between the YANG module in
RFC8049 and the YANG module in draft-wu-l3sm-rfc8049bis, or any non
backward compatible YANG modules.
- we need _an automatic way_ to make the link between the YANG module in
RFC8022 and the YANG module in draft-acee-netmod-rfc8022bis, or any new
YANG module names used for NMDA transition.
Note: actually, we face two different problems. draft-wu-l3sm-rfc8049bis
might be declared backward incompatible with RFC8049, while RFC8022bis
is backward compatible with RFC8022. The RFC8022bis went for a new YANG
module name ietf-routing-2 to avoid to document the -state tree (as
deprecated), based on the argument that ietf-routing is not yet implemented.
Which solutions do we have from here?
#1. We keep the same module name and express that the YANG module in
draft-wu-l3sm-rfc8049bis is not backward compatible with the RFC8049
one. This is the openconfig way. See draft-clacla-netmod-model-catalog
(and draft-openconfig-netmod-model-catalog before)
// extension statements
extension openconfig-version {
argument "semver" {
yin-element false;
}
description
"The OpenConfig version number for the module. This is
expressed as a semantic version number of the form:
x.y.z
where:
* x corresponds to the major version,
* y corresponds to a minor version,
* z corresponds to a patch version.
This version corresponds to the model file within which it is
defined, and does not cover the whole set of OpenConfig models.
Where several modules are used to build up a single block of
functionality, the same module version is specified across each
file that makes up the module.
A major version number of 0 indicates that this model is still
in development (whether within OpenConfig or with industry
partners), and is potentially subject to change.
Following a release of major version 1, all modules will
increment major revision number where backwards incompatible
changes to the model are made.
The minor version is changed when features are added to the
model that do not impact current clients use of the model.
The patch-level version is incremented when non-feature changes
(such as bugfixes or clarifications to human-readable
descriptions that do not impact model functionality) are made
that maintain backwards compatibility.
The version number is stored in the module meta-data.";
}
Similarly, we always keep the same YANG module name in case of NMDA
transition. So ietf-routing-2 should be changed back to ietf-routing.
The email thread "[Rtg-dt-yang-arch] ietf-routing or ietf-routing-2?
module naming convention for NMDA transition. Re: [netmod] upcoming
adoptions" seems to go in that direction.
#2. Or we have a different module name, let's say ietf-l3vpn-svc-2 or
ietf-routing-2 but then, how do we make the link with the previous module?
Then ... What? We create extension that will link the
draft-wu-l3sm-rfc8049bis YANG module to the RFC8049 YANG module? Same
principle as #1, but just more complex.
Or we have a new YANG keyword (this implies YANG 2.0)
<CODE BEGINS>file"ietf-l3vpn-...@2017-09-14.yang"
module ietf-l3vpn-svc-2 {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-l3vpn-svc";
prefix l3vpn-svc;
*_obsolete|update _*ietf-l3vpn-svc@2017-01-2
And whose responsibility is this to warn/push all authors of
ietf-routing YANG modules to move to ietf-routing-2? (*)
The following are non solution IMO:
- Going from the draft-wu-l3sm-rfc8049bis YANG _module _to the
draft-wu-l3sm-rfc8049bis _document _to lookup the IETF "obsolete" flag
in order to understand that the RFC8049 YANG module is obsolete is not
an automatic solution.
- Using the yangcatalog.org might be a solution as we track the derived
semantic, but this is just an offline trick. This is not what I call
"automatic way"
- Using the YANG module description field might be interesting, but
again this is not an "automatic way":
description
"This YANG module defines a generic service configuration
model for Layer 3 VPNs. This model is common across all
vendor implementations. This obsoletes the RFC8049 YANG
module, ietf-l3vpn-svc@2017-01-2";
revision 2017-09-14 {
description
"First revision ofRFC8049 <https://tools.ietf.org/html/rfc8049>.";
reference
"RFC xxxx: YANG Data Model for L3VPN Service Delivery";
In conclusion, I believe openconfig got this right and that solution #1
is the solution to go ... while waiting for a new YANG keyword in YANG 2.0
(*) If you want to change the module from ietf-routing to
ietf-routing-2, then you should follow with all authors of dependent
modules to make sure they transition to ietf-routing-2
In the yangcatalog.org, because I needed the information as OPS AD, we
created a small script to get that authors list for IETF drafts. For the
ietf-routing, this produces the following
{
"output": {
"author-email": [
"draft-ietf-mpls-static-y...@ietf.org",
"draft-ietf-mpls-base-y...@ietf.org",
"draft-ietf-ospf-sr-y...@ietf.org",
"draft-ietf-pim-y...@ietf.org",
"draft-ietf-bier-bier-y...@ietf.org",
"draft-zhang-bier-te-y...@ietf.org",
"draft-ietf-isis-yang-isis-...@ietf.org",
"draft-ietf-teas-yang-rsvp...@ietf.org",
"draft-ietf-mpls-mldp-y...@ietf.org",
"draft-zhao-pim-igmp-mld-snooping-y...@ietf.org",
"draft-ietf-isis-sr-y...@ietf.org",
"draft-acee-rtgwg-yang-rib-ext...@ietf.org",
"draft-ietf-pim-igmp-mld-y...@ietf.org",
"draft-ietf-i2rs-fb-rib-data-mo...@ietf.org",
"draft-ietf-ospf-y...@ietf.org",
"draft-ietf-rtgwg-yang-...@ietf.org",
"draft-ietf-spring-sr-y...@ietf.org",
"draft-ietf-teas-yang-r...@ietf.org",
"draft-ietf-i2rs-pkt-eca-data-mo...@ietf.org",
"draft-ietf-mpls-ldp-y...@ietf.org",
"draft-ietf-bfd-y...@ietf.org",
"draft-ietf-pim-msdp-y...@ietf.org"
]
}
}
Fortunately, we only deal with IETF dependent YANG modules in case of
the ietf-routing. That's an easier case.
If we would change ietf-interfaces to ietf-interfaces-2, we would have
an cross SDO issue ... Btw, there are no automatic ways to extract the
authors of YANG modules from different SDOs: it's only a metadata that
that the different SDOs should insert in the yangcatalog. So we would
have to rely on liaisons or direct emails, assuming we know the authors.
Time consuming, believe me.
Regards, Benoit
Hi,
As part of the my Routing Directorate review of
draft-wu-l3sm-rfc8049bis I noted that there were several incompatible
changes being made to the ietf-l3vpn-svc module without changing the
name. I raised this with the YANG doctors and others involved with the
draft and it surfaced some topics which really should be discussed here
in NetMod.
The background (as explained off-list by others, so I hope I have it
right) is that one of the YANG Doctors noted that RFC8049 was broken
and could not be implemented as defined, and therefore a fix was
needed. L3SM has concluded so the fix is in the individual draft
draft-wu-l3sm-rfc8049bis. Since the rfc8049 version of ietf-l3vpn-svc
module could not be implemented, the feeling by the YANG Dr was that
even though the new module is incompatible with the original definition
the module the rule defined in Section 11 of YANG 1.1 (or section 10 of
RFC 6020) didn't have to be followed and the same name could be used.
In the subsequent discussion with the YANG Drs., the general discussion
was heading down the path of using a new module name, and thereby not
violating YANG module update rules. This lead us back to the a similar
discussion we've been having in the context of 8022bis: how best to
indicate that a whole module is being obsoleted. RFCs do this by adding
'metadata' to the headers, e.g., "Obsoletes: 8049", but this doesn't
help YANG tooling. For 8022, we have one approach - publishing an
updated rev of the original module marking all nodes as deprecated - but
that doesn't really make sense for rfc8049bis.
So the discussion for the WG is:
How do we handle incompatible module changes, notably when one module
'obsoletes' another module -- from both the process and tooling
perspectives?
I know Benoit plans to bring in some thoughts/proposals, perhaps there
are others.
Cheers,
Lou
(as contributor/reviewer)
.
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