Re: [YANG] default values

Ladislav Lhotka wrote:
> Andy Bierman píše v Čt 17. 01. 2008 v 07:42 -0800:
>   
>> I strongly object to removing the default-stmt.
>> As Balazs pointed out, if a WG does not agree on a suitable
>> default value, they do not have to define one.  This clause
>> is needed to support NETCONF, not only to provide as much
>> machine-readable info about the data model characteristics,
>> but to simplify NETCONF tasks for operators and applications.
>>     
>
> Operators should only be concerned with the defaults used by their front
> ends - and these would typically include much more than just the MUST
> defaults that YANG can handle.
>
>   

Many operators want to know how to control the NE devices
in their network without relying on any magic 'front-end' that
always knows what values work on any given device.

NETCONF is designed to work, even if all the operator
has is 'ssh -s netconf -p 830' for access to the NETCONF agent.

>> There are likely to be many knobs in a real config file that are optional
>> and have suitable agent-supplied default values.  It is very useful
>>     
>
> How many of them could possibly be of the MUST sort? I don't know many.
> The default is a weak concept, it's not like a fixed constant.
>
>   

I disagree.
First, it is up to the protocol WG defining the knob, not the YANG WG.
Given that the protocol could define a range of compliant values for a
standard knob, it is one extra step to pick 1 of the compliant values as
the default.

A trivial example is a boolean knob (or presence container in YANG)
that represents some service or feature, and the WG agrees it is 'off' 
by default.

> Lada
>
>   

Andy

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