Re: [YANG] default values

Ladislav Lhotka wrote:
> Andy Bierman píše v St 16. 01. 2008 v 06:08 -0800:
> 
>> YANG has the "DEFVAL with teeth" that SMIv2 never had.
>> In YANG the default MUST be supported by the agent.
>> It is not just a suggestion.  This means the manager can
>> actually pay attention to the default defined in the data model,
>> and change it only if needed.
> 
> I understand this but, as a matter of fact, most defaults in protocol
> standards are of the SHOULD class at most. In a vendor-neutral
> environment, it would be much safer if each device fills all the blanks.
> 
>> On large NE devices, it is common practice to keep the CLI config file
>> as small as possible by only including non-default values.  NETCONF
>> needs to support this feature as well, and YANG leaf/typedef default does that.
> 
> Yes, but this is only possible because the CLIs are vendor-specific. It
> is quite common that different vendors use different defaults. If you
> try to enforce a single default in the data model, the vendor that
> thinks otherwise will come up with an entirely new data model (namespace
> URI) which is IMO much worse for interoperability.
> 

You are entering a new topic zone -- why the IETF has never been
successful in standardizing the configuration of any of its protocols.
After 20 years and a pathetic handful of standard writable knobs,
one has to ask if maybe there is some part of the problem space
that has been overlooked.

We will never have standard writable knobs until vendors understand
the concept of a standard, and make an effort to define some
standard knobs, which actually provide enough functionality
to configure the device.

It takes a lot of work to define the standard knob settings,
and protocol WGs usually decide not to bother with any configuration
at all.  But we make all our hammers and all our nails by hand,
so it is easy to get away with it.

(Lewis and Clark burned down some forts along the way, to
recover and reuse their precious handmade nails.  We need to
learn how to get machines to make the nails... ;-)

> Lada
> 

Andy

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