Re: [netmod] yang-push issue: draft-ietf-netconf-yang-push-12 and default values and RFC 6243

[Robert Wilton <[e-mail]>]

HI Alex,

Note, that when it comes to the NMDA <operational> datastore there are 
no default values.  Only the values that are "in use".

Thanks,
Rob


On 17/01/2018 19:09, Alexander Clemm wrote:
>
> Hi Einar,
>
> I suggest we add clarification that default values must be reported.  
> For on-change, clearly all changes need to be reported, whether the 
> change is to a default value or not, everything else would be 
> confusing.  Also for periodic, it would be confusing to leave out 
> readings when a value is at default  versus not (the object might also 
> have been deleted, etc).  So, I don’t think we need to add a flag or 
> such that would allow to exclude defaults which appear to be of 
> limited benefit to applications while introducing a lot more 
> complexity to deal with corner cases such as the ones described.
>
> --- Alex
>
> *From:*netmod [mailto:[e-mail]] *On Behalf Of *Einar 
> Nilsen-Nygaard (einarnn)
> *Sent:* Wednesday, January 17, 2018 5:27 AM
> *To:* [e-mail]
> *Subject:* [netmod] yang-push issue: draft-ietf-netconf-yang-push-12 
> and default values and RFC 6243
>
> All,
>
> In discussions with some customers and on implementation, the issue of 
> defaults has come up. For get/get-config we have the “with defaults 
> capability” defined in RFC 6243 that allows us to control the 
> behaviour with respect to defaults. To remind folk with an example, we 
> could have:
>
> <rpc message-id="101"
>
>  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
>
>   <get>
>
>     <filter type="subtree">
>
>       <interfaces xmlns="http://example.com/ns/interfaces"/>
>
>     </filter>
>
>     <with-defaults
>
>  xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults">
>
>       report-all
>
>     </with-defaults>
>
>   </get>
>
> </rpc>
>
> The addition of the “with-defaults” tag and value determines the 
> behavior of the get in this example (taken from A.3.1 in RFC 6243 
> <https://tools.ietf.org/html/rfc6243#page-22>).
>
> It strikes me that we need to have a similar mechanism for telemetry, 
> allowing a user to specify, for example, that for a periodic 
> subscription on a subtree, they also wish default values to be 
> reported. I think at minimum we need clarification on this, as section 
> 3.7 of draft-ietf-netconf-yang-push-12 currently says:
>
>     /The content of the update record is equivalent to the contents
>     that would be obtained had the same data been explicitly retrieved
>     using e.g., a NETCONF "get" operation, with the same filters applied./
>
> This text can currently only refer to a “get” as defined in RFC 6241 
> as there is no reference to RFC 6243 as yet. I think we need to 
> address this issue now to define expectations, even if it is to 
> explicitly not consider an RFC 6243-like mechanism or to say that we 
> only consider explicitly set values in telemetry, or…
>
> Cheers,
>
> Einar
>
>
>
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