Re: [netmod] draft-ietf-softwire-yang-13

Ladislav Lhotka <lhotka@nic.cz> Fri, 28 December 2018 07:47 UTC

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From: Ladislav Lhotka <lhotka@nic.cz>
To: tom petch <ietfc@btconnect.com>, Martin Bjorklund <mbj@tail-f.com>
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Date: Fri, 28 Dec 2018 08:47:41 +0100
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Subject: Re: [netmod] draft-ietf-softwire-yang-13
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tom petch <ietfc@btconnect.com> writes:

> ----- Original Message -----
> From: "Martin Bjorklund" <mbj@tail-f.com>
> To: <ietfc@btconnect.com>
> Cc: <netmod@ietf.org>
> Sent: Thursday, December 27, 2018 12:08 PM
>
>> tom petch <ietfc@btconnect.com> wrote:
>> > Martin
>> >
>> > The Acknowledgements for
>> > draft-ietf-softwire-yang-13
>> > thank you for your work on this I-D (on the IESG Telechat for 10th
>> > January 2019) so can you tell me where my YANG is going wrong.
>> >
>> > The module has
>> >   augment "/if:interfaces/if:interface" {
>> >     when "derived-from(if:type, 'iana-tunnel-type:aplusp')";
>> > and defines aplusp as a tunnel type in section 10.
>> >
>> > A suggestion I made last October was to have a base for the three
>> > protocols covered here - MAP-E, MAP-T, Lw406 - and then derive three
>> > separate entities therefrom for the three protocols; I can see no
>> > derivation.  In which case, when is
>> >
>> >     when "derived-from(if:type, 'iana-tunnel-type:aplusp')";
>> >
>> > going to be true?
>>
>> Right; either they have to define derived identities as you suggested,
>> or this need to change to 'derived-from-or-self'.
>
> ... or drop the 'derived' altogether; if there is only 'aplusp', as at
> present, then I see no need for 'derived' and inserting one
> unnecessarily leaves scope for a future addition to be true when it is
> not wanted.  I can see it either way.

Do you mean writing something like

    when "if:type = 'iana-tunnel-type:aplusp'";

?

This is brittle and shouldn't be used because it is a plain string
equality test and the result depends (in XML representation) on the
prefix that is declared for the namespace URI of the iana-tunnel-type
module.

It is true that derived-from/derived-from-or-self leaves scope for
future additions. However, if ever an identity is defined that
is derived from 'iana-tunnel-type:aplusp', then it IMO makes sense only
if the properties of the latter are inherited, so the "when" test
should still be true (and the augment applicable).

Lada

>
> Tom Petch
>
>>
>> /martin
>>
>
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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
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