Re: [YANG] mandatory & default

tom.petch wrote:
> ----- Original Message -----
> From: "Andy Bierman" <ietf@andybierman.com>
> To: "Phil Shafer" <phil@juniper.net>
> Cc: <yang@ietf.org>
> Sent: Monday, January 28, 2008 5:10 AM
> Subject: Re: [YANG] mandatory & default
> 
> 
>> Phil Shafer wrote:
>>> [replying to multiple Andy-grams]
>>>
>> We strongly disagree on the interpretation of RFC 4741
>> and whether a node with a default value really exists or not.
>>
>> It is very fragile SW design to assume the agent is using the exact default
>> that was tracked down in the documentation.
>>
>> It is up to the operator whether knowing that a node
>> is actually supported, and knowing the exact value set by the agent,
>> is a waste of space or important debugging information.
>>
> 
> I am very much with Andy (and Randy) on this one.  Knowing all the parameters
> that affect how a box functions is vital; it may be the only way to work out why
> it is not working as the operator thinks it should be.
> 
> I would say that having access to both the full and the specified configuration
> is a MUST.  If forced to choose which had to be implemented, I would go for the
> full configuration every time.  Computers can simply and reliably remove the
> extra information, they cannot (as) reliably insert the supposed defaults as
> known on the device.
> 

I think Juergen also agrees that access to all the parameters is sometimes
needed to debug a broken network.

I think there is some consensus that a mechanism is needed to retrieve
just the non-defaults, or retrieve everything.  I have already published
the 'with-defaults' mechanism:

http://www.ietf.org/internet-drafts/draft-bierman-ncx-ext-00.txt

There is no capability URI defined to advertise this extension.

I have also implemented 'per-session' parameters (ala set term)
to set the session default for the per-PDU 'with-defaults', to simplify
manager access.

At a minimum, there should also be a read-only leaf added to
the NETCONF Monitoring DM to indicate the agent-wide default
for the 'with-defaults' flag.  (Per session control is extra credit ;-)

An agent can leave out the defaults as the normal case if this
global flag is set to false.  However, the 'with-defaults=true' flag
must be honored when added to a get* or copy-config PDU.

> Tom Petch
> 
>> Andy

Andy

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