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

[Alexander Clemm <[e-mail]>]

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