[YANG] default values

> Yes, changing defaults is incompatible.  If you do that, you have to
> change the namespace.

BTW, that's exactly why I am against the default values in typedef: they
make the data model too specialised. The defaults could be easily
handled as follows:

1. The standard that defines the type specifies in plain RFC-English
that the default value MUST, SHOULD or MAY be something.

2. An implementor reflects this in a device, but is also required to
fill the default (or another) value in the initial startup
configuration.

3. The client needn't care about what the default is, it just queries
the device to see the actual value, changes it if necessary etc.

This approach would make the same data model reusable with other default
value and, in addition, allow for honouring the semantics of MUST,
SHOULD and MAY. The default in typedefs is only usable in the MUST case.

So my suggestion is to remove the default statement form YANG.

Lada

-- 
Ladislav Lhotka, CESNET
PGP Key ID: E74E8C0C

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