Re: [yang-doctors] question regarding conditional/optional statements

[Juergen Schoenwaelder <[e-mail]>]

On Fri, Aug 18, 2017 at 12:59:10PM +0000, Norm Strahle wrote:
> Hey folks, Appreciate all the feedback.  We discussed yesterday among diffserv-ietf modelers yesterday and had a couple comments:
> 
> 
> ·       We liked explicit statements (deviations, features, flag-bits) rather than implicit – i.e. option 5 – of vendors leaving unsupported leaves out of containers
> 
> ·       We think if-features or the “bit” flag mechanism are better than deviations, as it at least allows clients to anticipate up front that some items may not be supported.

A decent implementation will expect deviations, deviations are always
possible. I think there is a circular argument here, which boils down
to "we do not want to use deviations because we do not want to process
deviations".
 
> ·       One advantage of using the “bit” flag mechanism – i.e. option 2 - over features is that this allows a vendor to specify per-interface what is supported.  What features a vendor supports for diffserv is very hardware dependent and may vary from interface to interface within a single device. A device may have multiple types and generations of line cards, and thus, the types of stats supported will be different. The bit-flag mechanism allows a device to reflect that to the client explicitly.
>

As long as we talk about non-mandatory counters, simply not reporting
counters that do not exist seems to be the most simple solution. If
you want to tell clients upfront that a counter will never exist, use
the deviation mechanism. This is why we have it.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
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