Re: [netmod] [Netconf] LC of NDMA NETCONF/RESTCONF drafts

[Robert Wilton <[e-mail]>]

Hi Andy,


On 31/01/2018 09:22, Andy Bierman wrote:
>
>
> On Wed, Jan 31, 2018 at 12:11 AM, Juergen Schoenwaelder 
> <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     On Tue, Jan 30, 2018 at 12:35:33PM -0800, Andy Bierman wrote:
>     > Hi,
>     >
>     > I have some questions about these drafts.
>     >
>     > 1) what if datastore set to "conventional"?
>     >     There are many places where a datastore-ref type is used.
>     >     However, "conventional" is valid for base "datastore", even
>     though
>     >     it is ambiguous as a datastore selector.
>
>     We can add explicit text that an identity that does not resolve to a
>     datastore implemented by the server results in an invalid value error.
>
>
>
> OK
>
>     > 2) origin filter is limited to 1 source
>     >    This filtering seems rather limited.  A client must retrieve
>     > <with-origin> and check
>     >     all the values in use, then make repeated requests for each
>     source as a
>     > different
>     >     <origin-filter> leaf
>
>     If the client does <with-origin>, then it has all origin information
>     and it can filter locally. That said, we could make origin-filter a
>     leaf-list which is logically ORed so that one can retrieve
>     origin-filter=or:system or origin-filter=or:learned in one request.
>
>
>
> OK
>
>     > 3) with-defaults broken
>     >     The operational datastore does not support with-defaults.
>     >      Instead, the client must use origin-filter=or:default or
>     with-origin
>     >      and check all the origin attributes.  Since a client needs
>     to use
>     >      with-defaults for other datastores, this special handling of
>     > <operational>
>     >      seems unhelpful.
>
>     I think the with-defaults semantics for conventional configuration
>     datastores are much more complicated than necessary for the
>     operational state datastore. Note that that the operational state
>     datastore reports in-use values not really defaults:
>
>       <leaf or:origin='default'>foo</leaf>
>
>     This reports that the value 'foo' is in use and that it originates
>     from a default value. Note that this could also be
>
>       <leaf or:origin='intended'>foo</leaf>
>
>     in case the intended configuration datastore configured the value
>     'foo' (despite this value matching the default). The with-defaults
>     solution is pretty complex because it tries to handle how different
>     systems deal with configuration defaults. The idea is to not carry
>     this complexity over to in-use values in the operational state
>     datastore.
>
>
>
> Before NMDA, the client could decide if it wanted to retrieve default 
> nodes or not.
> This client-choice has been removed from NMDA, which is a problem.
We tried to reach a sensible compromise on the data returned from 
operational (defined in section 5.3 of the NMDA architecture):
  - it should return explicit values for everything that is affecting 
the actual running state of the device (regardless of whether the 
operational value matches a schema default value).
  - it does not need to, and should not, return operational values for 
stuff that isn't actually in use, i.e. don't return needless and 
unwanted data.

In particular, if no value is returned from a particular data node in 
<operational> then, barring mgmt protocol errors, a client can assume 
that any functionality associated with that data node is off (i.e. not 
in use).

Some examples to illustrate the behavior:

(i) If a protocol, e.g. OSPF,  is not enabled/running then <operational> 
does not need to return any data for it.  It would be reasonable to 
return a flag to indicate that OSPF is not enabled/running.

(ii) If you have some funky widget on an interface that defaults to 
being off and isn't being used then <operational> don't need to return 
any data for it.

(iii) But, if you have some funky widget on an interface that defaults 
to being on, then the server should return data for it.  If it is 
actually enabled, then it would indicate that it is on and return any 
associated values with its operational state, or if it is disabled then 
it should explicitly report that it is off.

(iv) I would regard that all applied configuration is "in use" by the 
system, even if it matches the default value, and hence it should be 
reported.


This behavior for <operational> is obviously slightly different from the 
existing with-default handling that is supported for configuration 
datastores.  As I recall, there were a couple of reasons that we decided 
to have a different behavior for <operational>:
(a) to have consistent semantics for all servers, rather than different 
servers supporting different with-defaults behaviors (which makes life 
harder for clients because they must cope with all variants).
(b) to remove any potential ambiguity if data isn't returned.  I.e. with 
the existing with-defaults semantics it is not clear to me that servers 
will always return an explicit value to indicate that a particular 
widget is off if the schema defines that the default it that is 
enabled.  If the server doesn't support a given widget at all, it is 
quite plausible that it will just return no data for it. In theory 
features/deviations should handle this, but those don't work so well if 
different linecards have different capabilities. Hence being explicit 
about stuff that is in use seems more robust.

Thanks,
Rob


>
>
>     /js
>
>
> Andy
>
>     --
>     Juergen Schoenwaelder           Jacobs University Bremen gGmbH
>     Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
>     Fax:   [phone]         <https://www.jacobs-university.de/
>     <https://www.jacobs-university.de/>>
>
>
>
>
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