Re: [Netconf] YANG Doctor question: empty mandatory choice?

"Einar Nilsen-Nygaard (einarnn)" <> Thu, 02 August 2018 16:10 UTC

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From: "Einar Nilsen-Nygaard (einarnn)" <>
To: Andy Bierman <>
CC: Kent Watsen <>, "" <>, "" <>
Thread-Topic: [Netconf] YANG Doctor question: empty mandatory choice?
Date: Thu, 2 Aug 2018 16:10:50 +0000
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Subject: Re: [Netconf] YANG Doctor question: empty mandatory choice?
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On 2 Aug 2018, at 16:25, Andy Bierman <<>> wrote:

On Thu, Aug 2, 2018 at 8:11 AM, Kent Watsen <<>> wrote:

I am sympathetic to Eric's and Einar's observation that a given subscription, having multiple receivers, is likely to have all the receivers using the same transport and encoding.

The thought behind this is that, assuming there are multiple distinct applications, each application will selfishly create its own subscription; it will not try to see if there is another existing subscription that matches its needs.

Thus, in effect, the *only* purpose for there being a *list* of receivers is for enabling high availability, which I think is okay.  I wish the text was clearer about this objective.

What I object to is the way that this restriction is currently implemented using identities, which requires the "notif" models to do something right.  Better would be a "must" expression that says the count of the descendants is exactly one.  Can you do that?

Is there a way to make multiple receivers per subscription optional-to-implement
(another YANG feature?)

einarnn> Speaking for Cisco, we’re just putting a deviation in that initially the max size of the receivers list is 1. I think having multiple receivers be a feature would complicate the model. I see no need for a feature here.

Anyone implementing configured subscriptions is forced to support multiple receivers.
Does that mean it is harmful to the Internet if only 1 receiver per subscription is allowed?

einarnn> Clearly it’s not harmful :-)

I was told this feature is required because it is too much of a burden on the client to
create a separate subscription for each receiver.  IMO this is nonsense, but I won't
implement configured subscriptions anyway.

einarnn> I know I’m an advocate of this feature, but it’s nothing to do with the burden on a client related to creating >1 configured subscription. It’s to do with efficiency for me for the use cases related to HA. We have feedback from customers that they want to see the devices be able to send the same feed to >1 (usually 2) consumers to deal with HA/redundancy and to allow for receiver-determined network path diversity. This gives options needed (IMO) options for how customers address this.



Kent // contributor


===== original message =====

I am wondering why we are reopening the issue of multiple encodings/transports per receiver vs per subscription?

Having single transport / encoding per subscription is a simpler design (feedback from implementors; simplifies dealing with any error conditions due to encoding that would affect one receiver but not others in the same subscription; Einar has explained this in the past) and, while I am in general a fan of general design, there does not seem to be business requirements and scenarios that demand this - and even if there were, this would constitute merely an optimization (since if you have different receivers who want different encodings/tranport, you can always simply create another subscription).

If in the future there is really desire to add this as an additional feature, we can put this into a -bis version.  (Adding stuff will be easier than taking things away.)  Let's just be done.

--- Alex

> -----Original Message-----
> From: Netconf [<>] On Behalf Of Martin
> Bjorklund
> Sent: Tuesday, July 31, 2018 7:51 AM
> To:<>
> Cc:<>;<>
> Subject: Re: [Netconf] YANG Doctor question: empty mandatory choice?
> Kent Watsen <<>> wrote:
> > [removing yang-doctors list, and updating subject line accordingly]
> >
> >
> > >> > Why do all receivers of a subscription have to use the same
> transport?
> > >>
> > >> This was something that Martin and Eric worked out before we did
> > >> the first Last Call.  Eric doesn't seem to know the particular
> > >> reason, other than Martin seems to think it’s easier.
> > >
> > > No; I personally also prefer a design where each receiver has its
> > > own transport + encoding.
> >
> > +1
> >
> >
> > > The original model had a common "encoding" for all receivers, and
> > > then a receiver-specific transport - I think this is even worse,
> >
> > Agreed.
> >
> >
> > > and suggested to have transport + encoding defined together
> > > preferrably receiver-specifc or else common for all receivers.
> > >
> > > If the WG now believes that the transport + encoding should be done
> > > per receiver, this should be fairly easy to change.
> >
> > I also prefer per receiver, and I think that doing so will simplify
> > the model, as neither the mandatory "transport" nor the [not
> > mandatory?] "encoding" leaves have to be specified.
> >
> > In particular, my thoughts are that the "notif" model should provide
> > for the encoding selection, if needed (it's not needed for NETCONF, or
> > COAP I imagine).
> I agree.  I think this would be a cleaner design.
> /martin
> >
> > In the case of RESTCONF, we could update the ietf-restconf-client and
> > ietf-restconf-server models to include an "encodings" leaf-list, to
> > configure the RESTCONF server which encodings it should support.  We
> > likely need to do something similar to configure which HTTP versions
> > should be supported.  Now, in a general RC server, the server could
> > support both but, if the restconf-notif draft has its own list of
> > restconf-servers (i.e., it uses the "restconf-server-grouping" itself,
> > see my July 19 email for a YANG example), then a constraint could be
> > added limiting the number "supported" to just one.  Thus, when the RC
> > server reboots, and connects to the receiver and *automatically* (no
> > client RPC) starts pushing notifications, it can know what encoding to
> > use.
> >
> > I'm still unsure if its legal for an RC server to automatically push
> > notifications without a client-initiated RPC of any sort, and I'm also
> > uncertain if supporting *configured* subscriptions for NC or RC is
> > needed (see my message July 20 email).  So, some of this may work
> > itself out as we progress.
> >
> > I know that we're not defining the *configured* notif drafts in this
> > first effort, the we are publishing the SN draft with a configuration
> > model, my only concern now is configuration model presented in the SN
> > draft.
> >
> >
> > Kent // contributor
> >
> >
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