Re: [Netconf] Anyone want just Configured Subscriptions?

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Tue, 10 July 2018 22:43 UTC

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Date: Wed, 11 Jul 2018 00:43:11 +0200
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: "Eric Voit (evoit)" <evoit@cisco.com>
Cc: Lou Berger <lberger@labn.net>, Kent Watsen <kwatsen@juniper.net>, Netconf <netconf@ietf.org>
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Subject: Re: [Netconf] Anyone want just Configured Subscriptions?
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On Tue, Jul 10, 2018 at 10:27:23PM +0000, Eric Voit (evoit) wrote:
> > From: Lou Berger, July 10, 2018 4:43 PM
> > 
> > On 7/10/2018 4:37 PM, Kent Watsen wrote:
> > >
> > >> So in short, after RFC 8071 call home, you get NC/RC client and
> > >> server starting with a <hello> exchange. Ideally, the client would
> > >> indicate its readiness to receive unsolicited notifications before
> > >> you push notifications to the client (and the notification sender may
> > >> even be interested to know that it is sending notifications to a
> > >> remote system that does not just drop them). So either the clients
> > >> invokes an RPC to start the notification flow or, if you want to
> > >> optimize one round trip, the client includes a special
> > >>
> > >>   :willing-to-receive-unsolicited-notifications
> > >>
> > >> capability in the <hello> exchange.
> > > I agree that a client-advertised capability would be goodness here,
> > > but it only works for NC-clients, there is no corollary for RC-clients.
> > >
> > > Maybe clients should send a "willing-to-receive-unsolicited-notifications"
> > > RPC instead?
> > or an an error when an unsolicited notification is received by a client that
> > doesn't support it.
> > (optimizing for what I think suspect will be the common case in the long
> > term...)
> 
> Effectively this is what draft-ietf-netconf-restconf-notif, section 4.2 defines now.  A successful POST of a "subscription-started" notification must occur before events are sent.  Failure to receiver an OK for the POST means an error to the publisher.
> 
> Some form of RESTCONF Call Home with capability advertisement could also occur before the "subscription-started" POST.  However this advertisement of client capabilities might not be needed for all implementations.
>

I fail to understand section 4.2. The first sentence already leaves me
puzzled:

   With HTTP2 connectivity established, a POST of each new
   "subscription-started" state change notification messages will be
   addressed to HTTP augmentation code on the receiver capable of
   accepting and acknowledging to subscription state change
   notifications.

What does this say? And why is this HTTP2 specific? The publisher is
the RC server, no? So the RC server does HTTP transactions agains the
client? This does not seem to have anything to do with how the call
home RFC works.

I am not saying that what Figure 3 shows won't work, it just has
nothing to do with call home. You are reversing the RC client and
server roles, call home only reverses the connection establishment
roles. Big difference.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>