Re: [Netconf] IETF 101 SN Question 1: Proper designation of receiver

[Martin Bjorklund <[e-mail]>]

Hi,


"Eric Voit (evoit)" <[e-mail]> wrote:
> > From: Martin Bjorklund, June 26, 2018 4:13 PM
> > Subject: Re: [Netconf] IETF 101 SN Question 1: Proper designation of
> > receiver
> > 
> > "Eric Voit (evoit)" <[e-mail]> wrote:
> > > > From: Martin Bjorklund, June 26, 2018 2:43 PM
> > > >
> > > > "Eric Voit (evoit)" <[e-mail]> wrote:
> > > > > > From: Martin Bjorklund, June 26, 2018 4:11 AM
> > > > > >
> > > > > > "Eric Voit (evoit)" <[e-mail]> wrote:
> > > > > > > > From: Kent Watsen, June 25, 2018 3:43 PM
> > > > > > > >
> > > > > > > > >> >> <kent-orig> Okay, glad to see that you embrace using
> > > > > > > > >> >> ietf-netconf-server, rather than ietf-netconf-client.
> > > > > > > > >> >> And I'll grant you that it's infinitely more likely
> > > > > > > > >> >> that the ietf-netconf-server module would be
> > > > > > > > >> >> implemented (i.e., the top-level /ncs:netconf-server
> > > > > > > > >> >> container exists), more so than the ietf-netconf-client
> > > > > > > > >> >> module
> > would be implemented.
> > > > > > > > >> >> The WG created the top-level /ncc:netconf- client
> > > > > > > > >> >> container more for the sake of symmetry than for
> > > > > > > > >> >> having a use-case for when it would be implemented.  I
> > > > > > > > >> >> think the question to ask is, is it
> > > > > > > > >> possible that a device wants to use SN but doesn't
> > > > > > > > >> *implement*
> > > > > > > > >> ietf-netconf- server?
> > > > > > > > >> >>
> > > > > > > > >> >> <Eric> Yes, this will be possible.  Reasons would include:
> > > > > > > > >> >> alternative
> > > > > > > > >> transports
> > > > > > > > >> >> (COMI, UDP), HTTP2 configured subscriptions (which
> > > > > > > > >> >> might use
> > > > > > > > >> >> ietf-restconf- server), or no need for a publisher to
> > > > > > > > >> >> include the configured subscriptions feature.
> > > > > > > > >> >>
> > > > > > > > >> >> <Kent> I should've be more specific: is it possible
> > > > > > > > >> >> that a device would use netconf-notif (where your
> > > > > > > > >> >> leafref is
> > > > > > > > >> >> defined) but not implement
> > > > > > > > >> ietf-netconf-
> > > > > > > > >> >> server?  Similarly, restconf-notif would presumably
> > > > > > > > >> >> have a leafref to
> > > > > > > > >> >> ietf-
> > > > > > > > >> >> restconf-server, etc.
> > > > > > > > >> >
> > > > > > > > >> >Yes.  Cases would include:
> > > > > > > > >> >(a) platform doesn't support configured subscriptions
> > > > > > > > >> >(b) vendor has not yet implemented ietf-netconf-server,
> > > > > > > > >> >and uses something
> > > > > > > > >> else.
> > > > > > > > >>
> > > > > > > > >> (a) is this a valid case?  - I thought this conversion
> > > > > > > > >> only regards configured subscriptions.  No leafref or
> > > > > > > > >> equivalent would be needed to support a dynamic subscription.
> > Right?
> > > > > > > > >
> > > > > > > > > Correct.  But your question was "can you use netconf-notif
> > > > > > > > > without a leafref
> > > > > > > > to...".
> > > > > > > > > Needing both drafts is absolutely the case for dynamic
> > > > > > > > > subscription support, and ietf-netconf-server would not be
> > > > > > > > > needed
> > > > here.
> > > > > > > >
> > > > > > > > I read the above a few times, but I'm having a hard time
> > > > > > > > understanding it.  Can say it differently or provide an example?
> > > > > > >
> > > > > > > Dynamic subscriptions over NETCONF requires
> > > > > > > draft-ietf-netconf-netconf-event-notifications.  With these
> > > > > > > deployments, there there is no call home, there is no
> > > > > > > configuration, and there need be no ietf-netconf-server.yang
> > > > > > > leafref (or use of ietf-netconf-server.yang grouping).
> > > > > > >
> > > > > > > > >> (b) this seems like a possibility, but then I think this
> > > > > > > > >> make the case for why a leafref to the global *conf
> > > > > > > > >> servers definitions won't always
> > > > > > > > work.
> > > > > > > > >
> > > > > > > > > Agree that nothing here will always work.  Deployments
> > > > > > > > > commonly will have a heterogeneous mixture of model
> > > > > > > > > ecosystem
> > > > models.
> > > > > > > > >
> > > > > > > > > This actually makes a *very* strong case for why the
> > > > > > > > > leafref should be added as an augmentation from the
> > > > > > > > > *conf-server
> > models.
> > > > > > > > > That way leafref augmentations are explicitly tied to the
> > > > > > > > > actual implementation of the
> > > > > > > > model against which they refer.
> > > > > > > >
> > > > > > > > Not in the *conf-server models, the augments go into the
> > > > > > > > *conf-notif models, I assume that is what you meant.
> > > > > > >
> > > > > > > My assertion is a good solution would be updating
> > > > > > > ietf-netconf-server.yang per what is below.  Note that an
> > > > > > > answer even further below regarding the sharing of a single
> > > > > > > NETCONF session across multiple subscriptions and typical
> > > > > > > RFC6241 protocol interactions is assumed.  But we could also
> > > > > > > insert your ietf-netconf-server.yang grouping just as
> > > > > > > effectively where the leafref is
> > > > seen.
> > > > > > >
> > > > > > > Anyway here are the following changes which would be made to
> > > > > > > ietf-netconf-server.yang
> > > > > > >
> > > > > > >   import ietf-subscribed-notifications { prefix sn; }
> > > > > > >   import ietf-netconf-subscribed-notifications { prefix nsn; }
> > > > > > >
> > > > > > >   feature subscription-support {
> > > > > > >     description
> > > > > > >         "The 'subscription-support' feature indicates that the
> > > > > > > NETCONF
> > > > server
> > > > > > >          supports configured subscriptions over call-home
> > > > > > >          connections.";
> > > > > > >        reference
> > > > > > >         "RFC xxxx: Customized Subscriptions to a Publisher's Event
> > Streams";
> > > > > > >      }
> > > > > > >
> > > > > > >  augment
> > > > > > >  "/sn:subscriptions/sn:subscription/sn:receivers/sn:receiver"
> > {
> > > > > > >    if-feature "subscription-support";
> > > > > > >    when 'derived-from(../../../transport, "nsn:netconf")';
> > > > > > >    description
> > > > > > >       "This augmentation allows NETCONF specific parameters to
> > > > > > > be
> > > > exposed
> > > > > > >       for a receiver.";
> > > > > > >     leaf netconf-endpoint {
> > > > > > >       type leafref {
> > > > > > >         path "/ncs:netconf-server/ncs:call-home/ncs:netconf-
> > > > client/ncs:name";
> > > > > > >       }
> > > > > > >       description
> > > > > > >         "Remote client which need to initiate the NETCONF transport
> > > > > > >         if
> > an
> > > > > > >         existing NETCONF session from that client is not
> > > > > > >         available.";
> > > > > > >     }
> > > > > > >   }
> > > > > > >
> > > > > > > With such a construct, it is impossible to add a leafref (or
> > > > > > > grouping) within ietf-subscribed-notifications unless
> > > > > > > ietf-netconf-server.yang exists.
> > > > > > >
> > > > > > > > >> This is why I
> > > > > > > > >> was thinking before that your modules might themselves
> > > > > > > > >> *use* the
> > > > > > > > >> *conf- server-groupings (while pruning out unneeded
> > > > > > > > >> parts, e.g., the "listen" subtree), so that it's
> > > > > > > > >> independent of what the system has implemented at the global
> > level.
> > > > > > > > >
> > > > > > > > > If you have 500 subscriptions, you then have to populate
> > > > > > > > > 500 identical
> > > > > > > > groupings.
> > > > > > > >
> > > > > > > > No, you have one grouping, with 500
> > > > > > > > /netconf-server/call-home/netconf-client
> > > > > > > > instances.
> > > > > > >
> > > > > > > Yes.  But I don't know why someone would voluntarily do add
> > > > > > > 500 repeated elements to a configuration datastore.
> > > > > > >
> > > > > > > > >  And yes this is possible.  But it makes the part of me
> > > > > > > > > which likes Normalized  data quite uncomfortable.
> > > > > > > > >
> > > > > > > > > But as I said before, it the WG wants such redundancy, fine.
> > > > > > > > > Either choice need not impact decisions as part of LC.
> > > > > > > >
> > > > > > > > I don't believe that is a WG-preference thing, so much as an
> > > > > > > > outcome of the current design, which is that each receiver
> > > > > > > > for each subscription has its own state-machine and protocol
> > > > > > > > messages.  There is no sharing; no two receives can use the
> > > > > > > > same RFC 6241 NETCONF session, which effectively translates
> > > > > > > > to each receiver having its own
> > > > > > > > /netconf-server/call-home/netconf-client
> > > > > > > > instance,
> > > > > > > > right?
> > > > > > >
> > > > > > > This is incorrect.  Protocol and state-machine messages have
> > > > > > > been decoupled from the transport session.
> > > > > > >
> > > > > > > I am not sure why you think that subscriptions are unable to
> > > > > > > use a common NETCONF session?  Implementations of dynamic
> > > > > > > NETCONF subscriptions have been doing this for years.
> > > > > > > Subscription multiplexing of configured and dynamic
> > > > > > > subscriptions over a common transport is a pre-requisite for
> > > > > > > solution
> > scalability.
> > > > > >
> > > > > > I don't think muliplexing of configured and dynamic
> > > > > > subscriptions over a single session is possible.
> > > > > >
> > > > > > If this is the intention of the current design, the document
> > > > > > needs to explain how this is supposed to be done.
> > > > >
> > > > > What is your concern?
> > > >
> > > > Suppose a client connects to a server and starts a dynamic
> > > > subscription.  Can this session somehow be used for a configured
> > subscription?  I assume not.
> > >
> > > Why not?
> > 
> > How would a server know that a certain configured receiver is the same
> > as an
> > ongoing session?  And as a client, suppose I just opened a session to
> > send one
> > request and then I plan to close the sesssion.  I probably don't want
> > notifs on
> > this session as well.
> 
> This is a valid scenario.  And while a fix for the current solution
> would be quite easy to do in text (i.e., through defining expectations
> of client behavior), it is not necessary to force this complexity on
> the client.  So instead I propose updating the first paragraph of
> NETCONF-notif, section 6.2 to the following:
> 
> "When a configured subscription enters the "valid" state, there is no
> guarantee a usable NETCONF transport session is currently in place
> with each associated receiver.  As a result, the first configured
> subscription to a specific receiver MUST establish a NETCONF transport
> session via NETCONF call home [RFC8071] , section 4.1.  This transport
> session MUST then be used by additional configured subscriptions
> targeting that the same receiver.  This same receiver is identifiable
> on the publisher as one which targets the same address and port used
> to establish the existing NETCONF call home connection.

This is not enough / correct.  You also need to take the user name
into account.

> This transport
> session MAY also be used by dynamic subscriptions and/or
> non-subscription related NETCONF operations originated by the NETCONF
> client.
> 
> Until a "subscription-started" state change notification is
> successfully sent for a configured subscription, that subscription's
> receiver MUST remain in either the "connecting" or the "timeout"
> state."
> 
> > > > > > Multiplexing multiple configured subscriptions over a single
> > > > > > transport session could be possible, but the document doesn't
> > > > > > mention
> > > > this.
> > > > > > Again, if this is the intention, it needs to be properly
> > > > > > described in the document.
> > > > >
> > > > > What is missing?  The subscribed-notification draft section 2.5.1
> > > > > and Figure 9 describe how each receiver is pushed their own state
> > > > > notifications.  (I.e., the state machine is per-receiver.  It is
> > > > > not per-subscription, nor is it per-transport.)
> > > >
> > > > If there are two different subscriptions configured, each has its
> > > > own list of receivers.  Under which circumstances will the server
> > > > decide to use a single transport session for these two different
> > subscriptions?
> > >
> > > If the "transport", "address", "port" are the same, then a single
> > > transport session can be used.
> > 
> > What if the encoding is different?  
> 
> When there really is a different encoding for NETCONF (which is
> currently not supported in accordance with you earlier comments), we
> have the option of adding "encoding" to the list of properties which
> demand a different transport.  However as there are not multiple
> encodings for NETCONF here, it is easy to ignore for now, especially
> as an implementation can simply define a different port for the target
> connection should the receiver really want different encoding someday.
> 
> > What if the users are different?
> 
> As you can identify specific ports with different call home, this will
> cover different users if a receiver can't de-multiplex.

The solution must be robust enough to correctly handle all cases that
it allows to be confgigured.

Anyway, if this whole issue is handled in the transport documents, I
am happy.  Some transports will likely support this, and some will
not.

> > Etc.  The point is that maybe there are cases when this can be done,
> > but you
> > need to spell this out.
> 
> For receiver configuration data right now, we just have receiver
> "name" which is a string.  There is no need to tell vendors how to do
> call home configuration as this isn't really in scope.  Solutions here
> will come soon enough with Kent's draft.
> 
> > > During the reviews however, you and Kent have argued away both "port"
> > > and "address" from being objects under the receiver.  So vendor
> > > specific augmentations will be needed to identify "address"
> > > and "port".
> > 
> > I expect such objects to be added by the transport docs, not by
> > vendors
> > (except for vendor-specific transports).
> 
> Per the parallel thread with Kent, I fully support augmenting the call
> home document when it is ready.
> 
> I think what we have now is fine.  Note: we can always re-add
> "address" and "port" back to SN if enough people want to re-insert
> explicit receiver identification within the YANG model

No!  That would be a big mistake, since address and port are not
enough for receiver identification.  Hopefully you agree by now.


> , and not leave
> it up to vendors.  But we have already argued this one sufficiently.
> I would rather just declare the current solution sufficient.
> 
> > > (Unless you are now ok with letting these objects back into the draft,
> > > just for the purposes of enable this a common receiver transport
> > > session identification.)  The other option is to have a future leafref
> > > augmented to ietf-netconf-server.yang as described above.
> > 
> > >
> > > >  I can't see any text about this in the document.
> > >
> > > I have added the following to the NETCONF-Notif document section on
> > configured subscriptions:
> > >
> > 
> > > "It is possible to have multiple configured subscriptions sharing a
> > > common transport to a single receiver.  The method of identifying that
> > > a receiver happens to be the same as used with another subscription is
> > > left up to implementers of this specification."
> > 
> > I don't think this helps.  It means that the client has no way of
> > knowing on
> > which sessions to expect notifs.
> 
> You are right that it won't be in the YANG file.  But that is the
> result when you argued "address" and "port" out of receivers.

See above.


/martin



> So for
> now the configuration is buried in vendor specific call home
> information.  That information of course can be referenced by vendor
> specific additions.
> 
> I think it best to leave it as is.  And at some point we will have the
> ietf-netconf-server.yang model which will allow the vendor specific
> part go away.
> 
> Eric
>  
> > > The text above can be changed if you are ok with adding "address"
> > > and "port" back into the draft.
> > >
> > > > > > This said, "session sharing" can be acheived with the current
> > > > > > design, as well as with the alternative design where the
> > > > > > protocol is defined per receiver rather than per subscription.
> > > > >
> > > > > Agree.  Any issues with NETCONF transport multiplexing of
> > > > > subscriptions
> > > > should be independent of the receiver YANG model.
> > > > >
> > > > > > But it won't be interoperable unless it is described.
> > > > >
> > > > > Likely NETCONF specific concerns would land in the NETCONF-notif.
> > > > > I am
> > > > happy to make any needed clarifications.
> > > >
> > > > I think you will need specific text in both subscribed-notifications
> > > > and in the transport drafts, if this is what you want to support.
> > >
> > > I have added text to NETCONF-notif per above.
> > >
> > > For subscribed-notifications, I have added the sentence to the first
> > > paragraph
> > of the "configured subscriptions" section:
> > >
> > > "Multiple configured subscriptions MUST be supportable over a single
> > > transport session."
> > 
> > See above.
> > 
> > 
> > /martin
> > 
> > 
> > 
> > >
> > > >
> > > > /martin
> > > >
> > > >
> > > >
> > > > >
> > > > > Eric
> > > > >
> > > > > > /martin
> > > > >
> > >
>