Re: [L3sm] New Version Notification for draft-wu-l3sm-rfc8049bis-03.txt

David Ball <daviball@cisco.com> Tue, 12 September 2017 07:38 UTC

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To: "Jan Lindblad (jlindbla)" <jlindbla@cisco.com>, Qin Wu <bill.wu@huawei.com>
Cc: l3sm <l3sm@ietf.org>, "Benoit Claise (bclaise)" <bclaise@cisco.com>, adrian <adrian@olddog.co.uk>
References: <B8F9A780D330094D99AF023C5877DABA9AAFC86C@nkgeml513-mbx.china.huawei.com> <b85886fa-7f8f-3e56-a8cb-7d72c4828fba@cisco.com> <B8F9A780D330094D99AF023C5877DABA9AB0DDDD@nkgeml513-mbx.china.huawei.com> <B5B3032C-A0CB-4BD0-9497-191F2554F723@cisco.com>
From: David Ball <daviball@cisco.com>
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Date: Tue, 12 Sep 2017 08:37:56 +0100
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Subject: Re: [L3sm] New Version Notification for draft-wu-l3sm-rfc8049bis-03.txt
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Completely agree.  In the case in question (address-allocation-type 
leaves), no value means "IPv4/IPv6 is not enabled for this 
site-network-access".


     David


On 12/09/2017 07:54, Jan Lindblad (jlindbla) wrote:
> Qin, team,
>
>>  *
>>
>>
>>     For the address-allocation-type leaves, I saw you removed the
>>     default (as agreed) but also added 'mandatory true' (which was
>>     not discussed).  Making these leaves mandatory does not address
>>     the problem - if anything, it makes it worse.  (Issue 15 from
>>     draft-02)
>>
>> [Qin]: Fine to me, it looks we need to seek balance between making 
>> all parameters mandatory and making all parameters optional. I hope 
>> Jan will be happy with these changes.
>
> Sometimes mandatory true is needed to make a sane model, but mandatory 
> elements also tend to make a model clunky, examples large etc. So I 
> generally like optional elements. The problem with optional elements 
> is people tend to forget that it may not be obvious what a system is 
> supposed to do when there is no value specified. Adding a default or 
> text in the description is therefore important. At the end of the day, 
> we're writing a contract. For interoperability to happen, there must 
> be no holes in the contract that are open to (differing) interpretation.
>
> So sure, you can have optional elements (this should even be the 
> normal case), and they don't need to have a default statement. But if 
> so, *describe* what it means; what the system is supposed to do. No 
> value is also a value.
>
> Best,
> /jan
>

-- 
David Ball
<daviball@cisco.com>;