Re: [netmod] backward compatibility requirements in draft-verdt-netmod-yang-versioning-reqs-00

Juergen Schoenwaelder <> Sat, 21 July 2018 10:12 UTC

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Date: Sat, 21 Jul 2018 12:12:23 +0200
From: Juergen Schoenwaelder <>
To: Andy Bierman <>
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Subject: Re: [netmod] backward compatibility requirements in draft-verdt-netmod-yang-versioning-reqs-00
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On Sat, Jul 21, 2018 at 01:48:37AM -0700, Andy Bierman wrote:
> But you can tell the 2 subtrees apart this way.
> If I change /foo from a container to a list, then how do you support both
> implementations
> of container /foo and list /foo at the same time?

Well, all of this is the consequence of moving from the current naming
system (module, path) to (module,path,version). Once we allow
non-backwards compatible changes, then we may have to find ways to
support different versions of a module (i.e, during session
establishment the client selects a version context to work with).

To be clear about my involvement in the versioning design team: I am
personally not convinced that a different versioning scheme is going
to be simpler; certain things that are simple and robust today will
become more complex and fragile. I decided to get involved in order to
point out that moving to a (module,path,version) naming scheme has
many implications since everywhere where we currently use
(module,path) we need to think about now required version context is
coming from. This goes far beyond YANG imports, this impacts likely
protocols, the proposed instance document storage format, NACM rules
may need to be interpreted in a version context etc.


Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103         <>