Re: [pim] [yang-doctors] Optional key support?

[Andy Bierman <[e-mail]>]

On Wed, Oct 24, 2018 at 8:56 AM, Robert Wilton <[e-mail]> wrote:

> It looks like the final reason that it was not accepted was because the
> change was regarded as being too big for YANG 1.1.  As such, it seems
> reasonable for this issue to be on Yang.next and considered again.
>
>
My objection to it was that it had a huge impact on the protocols and the
implementations.
The added complexity is not worth it.

It is not that hard to define a value that indicates "not really used".
That is not the same as "use the default".  Doing this in an elegant way
instead of ad-hoc requires coordinated solutions in YANG, protocols, and
servers.

There are probably lots of complex YANG text changes because the concept of
an
instance (and an instance-identifier) is so different. Also augment,
leafref,
and other cross-model dependencies are impacted.


Thanks,
> Rob
>



Andy


>
> On 24/10/2018 15:53, Acee Lindem (acee) wrote:
>
>> Read through the discussion and it is a shame we can't converge on a
>> solution. Is YANG 1.0 compatibility the major issue?
>> Thanks,
>> Acee
>>
>> On 10/24/18, 1:48 AM, "yang-doctors on behalf of Martin Bjorklund" <
>> [e-mail] on behalf of [e-mail]> wrote:
>>
>>      Andy Bierman <[e-mail]> wrote:
>>      > Hi,
>>      >
>>      > It has been discussed before.
>>      > It is already allowed for config=false nodes so the change would
>> be to
>>      > allow config=true nodes
>>      > to have no keys.
>>      >
>>      > Each time it comes up, somebody mentions that
>>      > (a) NETCONF/RESTCONF has no mechanism to delete all list entries
>>      > (b) The client cannot create more than 1 entry. How does the
>> server know
>>      >      the next entry is a different instance or replacing the first
>> instance?
>>           I don't think these were the reasons.  See the proposal that
>> was on
>>      the table for 1.1:
>>           http://svn.tools.ietf.org/svn/wg/netmod/yang-1.1/issues.html
>> #sec-10
>>           and the discussion:
>>           https://mailarchive.ietf.org/arch/browse/netmod/?gbt=1&index
>> =bwacmVipuJMakMFjDXXCZMXCTAA
>>                     /martin
>>                > What is the use-case for a config list without keys?
>>      >
>>      >
>>      > Andy
>>      >
>>      >
>>      > On Tue, Oct 23, 2018 at 2:16 PM, Reshad Rahman (rrahman) <
>> [e-mail]>
>>      > wrote:
>>      >
>>      > > <Changed subject>
>>      > >
>>      > >
>>      > >
>>      > > Hi Xufeng,
>>      > >
>>      > >
>>      > >
>>      > > I don’t know if this has been discussed for yang-next but it
>> doesn’t seem
>>      > > to be in the yang-next list. I believe optional keys were
>> discussed for
>>      > > YANG1.1, maybe others on the YD list remember…
>>      > >
>>      > > https://github.com/netmod-wg/yang-next/issues
>>      > >
>>      > >
>>      > >
>>      > > In this case, I believe it would have been useful to have that
>>      > > functionality.
>>      > >
>>      > >
>>      > >
>>      > > Regards,
>>      > >
>>      > > Reshad.
>>      > >
>>      > >
>>      > >
>>      > > *From: *Xufeng Liu <[e-mail]>
>>      > > *Date: *Tuesday, October 23, 2018 at 4:39 PM
>>      > > *To: *"Reshad Rahman (rrahman)" <[e-mail]>
>>      > > *Cc: *"[e-mail]" <[e-mail]>, Mahesh Sivakumar <
>>      > > [e-mail]>, Stig Venaas <[e-mail]>,
>> Guofeng <
>>      > > [e-mail]>, Anish Peter <[e-mail]>, "
>>      > > [e-mail]" <[e-mail]>, Liuyisong <
>>      > > [e-mail]>, Pete McAllister <
>> [e-mail]>, "
>>      > > [e-mail]" <[e-mail]>
>>      > > *Subject: *Re: [yang-doctors] [pim] Yangdoctors last call review
>> of
>>      > > draft-ietf-pim-igmp-mld-yang-07
>>      > >
>>      > >
>>      > >
>>      > > Hi Reshad and All,
>>      > >
>>      > >
>>      > >
>>      > > Do you think that it would be useful to eventually extend YANG
>> spec to
>>      > > allow an optional key with a default value? That would allow the
>> user not
>>      > > to enter the extra empty string, and make the model more user
>> friendly.
>>      > >
>>      > >
>>      > >
>>      > > Thanks,
>>      > >
>>      > > - Xufeng
>>      > >
>>      > >
>>      > >
>>      > > On Fri, Oct 19, 2018 at 11:02 AM Reshad Rahman (rrahman) <
>>      > > [e-mail]> wrote:
>>      > >
>>      > > Hi Xufeng,
>>      > >
>>      > >
>>      > >
>>      > > I think we should go with the solution proposed by Chris
>> (attached) when
>>      > > we last discussed this. I realize it’s not ideal but IMO it’s
>> better than
>>      > > other proposals.
>>      > >
>>      > >
>>      > >
>>      > > Regards,
>>      > >
>>      > > Reshad.
>>      > >
>>      > >
>>      > >
>>      > > *From: *yang-doctors <[e-mail]> on behalf
>> of Xufeng
>>      > > Liu <[e-mail]>
>>      > > *Date: *Friday, October 19, 2018 at 9:21 AM
>>      > > *To: *"[e-mail]" <[e-mail]>
>>      > > *Cc: *Mahesh Sivakumar <[e-mail]>, Stig
>> Venaas <
>>      > > [e-mail]>, Guofeng <[e-mail]>, Anish Peter <
>>      > > [e-mail]>, "[e-mail]" <
>> [e-mail]>,
>>      > > Liuyisong <[e-mail]>, Pete McAllister <
>>      > > [e-mail]>, "[e-mail]" <[e-mail]>
>>      > > *Subject: *Re: [yang-doctors] [pim] Yangdoctors last call review
>> of
>>      > > draft-ietf-pim-igmp-mld-yang-07
>>      > >
>>      > >
>>      > >
>>      > > Hi Jan,
>>      > >
>>      > >
>>      > >
>>      > > Thanks for reviewing.
>>      > >
>>      > > For #1, as discussed, there is no other better solution at the
>> moment.
>>      > > What would you suggest?
>>      > >
>>      > > Thanks.
>>      > >
>>      > > - Xufeng
>>      > >
>>      > >
>>      > >
>>      > > On Fri, Oct 19, 2018 at 4:25 AM Jan Lindblad <[e-mail]>
>> wrote:
>>      > >
>>      > > Feng,
>>      > >
>>      > >
>>      > >
>>      > > Hi Jan,
>>      > >
>>      > >
>>      > >
>>      > > We updated  draft-ietf-pim-igmp-mld-yang according to the
>> comments #2 ~
>>      > > #7, while Xufeng and you had discussed about comment #1.
>>      > >
>>      > > Please review the draft, thanks a lot.
>>      > >
>>      > > https://www.ietf.org/id/draft-ietf-pim-igmp-mld-yang-08.txt
>>      > >
>>      > >
>>      > >
>>      > > Good. I looked through the points #2-#7 and find that the work
>> group have
>>      > > understood and fixed those issues. #1 still remains to be
>> resolved. I can
>>      > > do a full re-review of the module once that one has been
>> resolved as well..
>>      > > Are there any outstanding questions on how to fix #1?
>>      > >
>>      > >
>>      > >
>>      > > Best Regards,
>>      > >
>>      > > /jan
>>      > >
>>      > > --
>>      > >
>>      > > *Jan Lindblad*, [e-mail], [phone]
>>      > >
>>      > > Solutions Architect, Business Development, Tail-f
>>      > >
>>      > > Tail-f is now a part of Cisco
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > > Feng
>>      > >
>>      > >
>>      > >
>>      > > -----Original Message-----
>>      > >
>>      > > From: Jan Lindblad [mailto:[e-mail] <[e-mail]>]
>>      > >
>>      > > Sent: Monday, August 13, 2018 10:35 PM
>>      > >
>>      > > To: [e-mail]
>>      > >
>>      > > Cc: [e-mail]; [e-mail]; draft-ietf-pim-igmp-mld-yang.a
>> [e-mail]
>>      > >
>>      > > Subject: Yangdoctors last call review of
>> draft-ietf-pim-igmp-mld-yang-07
>>      > >
>>      > >
>>      > >
>>      > > Reviewer: Jan Lindblad
>>      > >
>>      > > Review result: On the Right Track
>>      > >
>>      > >
>>      > >
>>      > > This is my YANG-doctor review of draft-ietf-pim-igmp-mld-yang-07.
>> In the
>>      > > spring, I did an early review of the -02 version.
>>      > >
>>      > >
>>      > >
>>      > > Most of the comments from the earlier review are still valid. In
>> some ways
>>      > > the document has progressed since -02, in many it has not, and
>> in a few it
>>      > > has deteriorated. In my judgement, the document is not ready for
>> last call.
>>      > > Many fundamentally important questions are still unresolved.
>> Here are my
>>      > > review comments in rough falling order of importance.
>>      > >
>>      > >
>>      > >
>>      > > #1 Improper augment of /rt:routing/rt:control-plane-protocols
>>      > >
>>      > >
>>      > >
>>      > > Quoted from section 3.1:
>>      > >
>>      > >    This model augments the core routing data model "ietf-routing"
>>      > >
>>      > >    specified in [RFC8349].  The IGMP model augments "/rt:routing/
>>      > >
>>      > >    rt:control-plane-protocols" as opposed to augmenting
>> "/rt:routing/
>>      > >
>>      > >    rt:control-plane-protocols/rt:control-plane-protocol", as
>> the latter
>>      > >
>>      > >    would allow multiple protocol instances, while the IGMP
>> protocol is
>>      > >
>>      > >    designed to be enabled or disabled as a single protocol
>> instance on
>>      > >
>>      > >    a network instance or a logical network element.
>>      > >
>>      > >
>>      > >
>>      > > The description above, and the actual augment statements in the
>> YANG
>>      > > module violate the principles described in RFC 8349, the
>> ietf-routing.yang
>>      > > module it augments. In RFC 8349, section 5.3.  Control-Plane
>> Protocol, the
>>      > > proper way of augmenting the routing module is described. The
>> fact that
>>      > > this is a singleton protocol instance doesn't change this.
>> Section 5.3
>>      > > describes singleton cases as well.
>>      > >
>>      > >
>>      > >
>>      > > Guofeng: Xufeng has discussed with Jan about the comment, and it
>> is closed.
>>      > >
>>      > >
>>      > >
>>      > > #2 Incorrect vendor refinement model
>>      > >
>>      > >
>>      > >
>>      > > Quoted from section 2.2:
>>      > >
>>      > >    For the same reason, wide constant ranges (for example, timer
>>      > >
>>      > >    maximum and minimum) will be used in the model.  It is
>> expected that
>>      > >
>>      > >    vendors will augment the model with any specific restrictions
>> that
>>      > >
>>      > >    might be required. Vendors may also extend the features list
>> with
>>      > >
>>      > >    proprietary extensions.
>>      > >
>>      > >
>>      > >
>>      > > This is not acceptable. The principle suggested does not foster
>>      > > interoperability and useful standards. It is also not possible
>> to do what
>>      > > the paragraph suggests in YANG. This was pointed out in the -02
>> review, and
>>      > > a suggestion was given there on how to address the problem.
>>      > >
>>      > >
>>      > >
>>      > > Guofeng: We removed the paragraph above, and put the values
>> discussed by
>>      > > Mcast Design Team.
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > > #3 Top level structures not optional
>>      > >
>>      > >
>>      > >
>>      > > Quoted from section 2.3:
>>      > >
>>      > >    The current document contains IGMP and MLD as separate schema
>>      > >
>>      > >    branches in the structure. The reason for this is to make it
>> easier
>>      > >
>>      > >    for implementations which may optionally choose to support
>> specific
>>      > >
>>      > >    address families. And the names of objects may be different
>> between
>>      > >
>>      > >    the IPv4 (IGMP) and IPv6 (MLD) address families.
>>      > >
>>      > >
>>      > >
>>      > > This problem was also pointed out in the -02 review. The author
>> suggests
>>      > > that implementing igmp and/or mld is optional. This is not
>> reflected in the
>>      > > YANG module, however. As currently modeled, both are currently
>> mandatory to
>>      > > implement. If-feature is used liberally in the module, and could
>> be used
>>      > > here as well.
>>      > >
>>      > >
>>      > >
>>      > > #4 Unclear meaning of optional leaves
>>      > >
>>      > >
>>      > >
>>      > > Quoted from section 3.1:
>>      > >
>>      > >    Where fields are not genuinely essential to protocol
>> operation, they
>>      > >
>>      > >    are marked as optional. Some fields will be essential but
>> have a
>>      > >
>>      > >    default specified, so that they need not be configured
>> explicitly.
>>      > >
>>      > >
>>      > >
>>      > > In fact, in the current version of the module, every leaf is
>> optional
>>      > > (except keys, which cannot be optional). It is good to see the
>> addition of
>>      > > defaults in many cases, but many unclear cases remain. E.g. leaf
>>      > > /igmp/global/enable is of type boolean. I understand what true
>> and false
>>      > > implies for this leaf. But what does it mean if it is not set at
>> all?
>>      > > Either add a default or describe the meaning in the description.
>> Similarly,
>>      > > if the leaf version is not set on an igmp or mld interface, or
>> on the
>>      > > interface-global level, what does that mean?
>>      > >
>>      > > Add default. require-router-alert? explicit-tracking?
>> exclude-lite? Many
>>      > > of these are used in NP-containers inheriting all the from the
>> root, which
>>      > > makes the use of mandatory highly discouraged in the current
>> form. If the
>>      > > RFC 8349 augmentation principles are followed, the concern
>> around mandatory
>>      > > falls, and some leafs with no sensible default could be marked
>> mandatory
>>      > > instead.
>>      > >
>>      > >
>>      > >
>>      > > #5 All optional state
>>      > >
>>      > >
>>      > >
>>      > > All state data is optional, which means a conforming server
>> could very
>>      > > well decide not to implement it. E.g. discontinuity-time is
>> optional.
>>      > > Should a manager count on this being available? A situation
>> where every
>>      > > leaf is optional is as nice and flexible for server implementors
>> as it is
>>      > > frustrating and complicated for manager implementors to consume.
>> A YANG
>>      > > model is an API contract and should consider the needs of both
>> sides. The
>>      > > way this has been designed reveals that no representation for
>> the consumer
>>      > > side of this model has been involved in the design. I would
>> suggest
>>      > > thinking through what is the most essential state data for a
>> manager, and
>>      > > make some leafs mandatory.
>>      > >
>>      > >
>>      > >
>>      > > #6 Abundant copy-paste
>>      > >
>>      > >
>>      > >
>>      > > There is abundant repetition in the YANG module. leaf version is
>> defined 2
>>      > > times for igmp with identical definitions, and two more for mld
>> with
>>      > > identical definitions. leaf enable is defined once for the
>> interface
>>      > > global-level, and with identical definition on the interface
>> local level.
>>      > > leaf last-member-query-interval, query-interval and half a dozen
>> other
>>      > > leaves are defined twice with identical definitions.
>>      > >
>>      > >
>>      > >
>>      > > #7 Leaf interface in the rpc clear*groups on line 1124, 1094 has
>> type
>>      > > string.
>>      > >
>>      > > Should be a leafref? Describe what values are valid. #8 Leaf
>> group-policy,
>>      > > source-policy on line 486, 527, 624, 689: type string. Should be
>> leafref?
>>      > >
>>      > > Describe what values are valid. #9 Leaf group on line 705, 1101,
>> 1131: Is
>>      > > any
>>      > >
>>      > > ipv4/6 address ok, or only a multicast address? Model
>> accordingly.
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > > *From:* pim [mailto:[e-mail] <[e-mail]>]
>> *On
>>      > > Behalf Of *Jan Lindblad
>>      > > *Sent:* Tuesday, September 11, 2018 9:52 PM
>>      > > *To:* Xufeng Liu <[e-mail]>
>>      > > *Cc:* [e-mail]; ietf <[e-mail]>; [e-mail];
>>      > > [e-mail]
>>      > > *Subject:* Re: [pim] Yangdoctors last call review of
>>      > > draft-ietf-pim-igmp-mld-yang-07
>>      > >
>>      > >
>>      > >
>>      > > Xufeng,
>>      > >
>>      > >
>>      > >
>>      > > Thanks for the review and valuable comments.
>>      > >
>>      > >
>>      > >
>>      > > In regard to item #1, there was a discussion thread among the
>> Yang
>>      > > Doctors, authors of RFC 8349, and Routing Area Yang Architecture
>> Design
>>      > > Team, as attached below.  The discussion occurred during the
>> review of a
>>      > > draft with the same issue as this one.
>>      > >
>>      > >
>>      > >
>>      > > I see, didn't know. Good. If this has been discussed to
>> conclusion, then
>>      > > you should of course go with that decision.
>>      > >
>>      > >
>>      > >
>>      > > As mentioned earlier, there are a few other singleton protocols
>> mapped
>>      > > into this structure, e.g. static. I think it would make sense to
>> treat this
>>      > > the same. Principle of least astonishment.
>>      > >
>>      > >
>>      > >
>>      > > Best Regards,
>>      > >
>>      > > /jan
>>      > >
>>      > >
>>      > >
>>      > >
>>      > >
>>      > > ================================
>>      > >
>>      > > 原始邮件
>>      > > 发件人：XufengLiu <[e-mail]>
>>      > > 收件人：Acee Lindem (acee) <[e-mail]>Christian Hopps <
>> [e-mail]>Martin
>>      > > Bjorklund <[e-mail]>
>>      > > 抄送人：张征00007940;[e-mail] <[e-mail]>
>>      > > 日 期 ：2018年02月20日 22:30
>>      > > 主 题 ：RE: [yang-doctors] How to restrict to have
>>      > > singlecontrol-plane-protocol instance
>>      > > Using "" as the name is better, but I am not sure that it is
>> good enough.
>>      > > When we use ConfD to translate the model to a command line, if
>> the option
>>      > > "tailf:cli-expose-key-name" is not used, we will have:
>>      > >
>>      > > edit routing control-plane-protocols control-plane-protocol type
>> msdp name
>>      > > ''"
>>      > >
>>      > > If the option "tailf:cli-expose-key-name" is used, we will have:
>>      > >
>>      > > edit routing control-plane-protocols control-plane-protocol msdp
>> ''"
>>      > >
>>      > > I am pretty sure that we would get a bug report on this, asking
>> what is
>>      > > the purpose to have: name ''", and requesting a suppression on
>> the term,
>>      > > but we do not have a good way to achieve.
>>      > >
>>      > > As a comparison, the option #3 will give:
>>      > >
>>      > > edit routing control-plane-protocols msdp
>>      > >
>>      > > This is the only acceptable solution so far. When a model is not
>> usable by
>>      > > the end-user, other considerations (such as augmentation
>> convenience) will
>>      > > not matter.
>>      > >
>>      > > Thanks,
>>      > > - Xufeng
>>      > >
>>      > > > -----Original Message-----
>>      > > > From: Acee Lindem (acee) [mailto:[e-mail]]
>>      > > > Sent: Monday, February 19, 2018 1:35 PM
>>      > > > To: Christian Hopps <[e-mail]>; Martin Bjorklund <
>>      > > [e-mail]>
>>      > > > Cc: Xufeng Liu <[e-mail]>; [e-mail];
>> yang-
>>      > > > [e-mail]
>>      > > > Subject: Re: [yang-doctors] How to restrict to have single
>> control-plane-
>>      > > > protocol instance
>>      > > >
>>      > > >
>>      > > >
>>      > > > On 2/19/18, 5:02 AM, "Christian Hopps" <[e-mail]>
>> wrote:
>>      > > >
>>      > > >
>>      > > >     Martin Bjorklund <[e-mail]> writes:
>>      > > >
>>      > > >     > Hi,
>>      > > >     >
>>      > > >     > "Acee Lindem (acee)" <[e-mail]> wrote:
>>      > > >     >> All,
>>      > > >     >>
>>      > > >     >> As seems to be the modus operandi for YANG issues, we
>> have 3
>>      > > separate
>>      > > > opinions as to how a protocol only supporting a single
>> instance should be
>>      > > > realized.
>>      > > >     >>
>>      > > >     >>   1. Augment the existing control plane protocols list
>> (RFC
>>      > > 8022BIS)
>>      > > >     >>   and specify in the description text that only a
>> single instance
>>      > > is
>>      > > >     >>   supported.
>>      > > >     >>   2. Augment the existing control plane protocols list
>> (RFC
>>      > > 8022BIS)
>>      > > >     >>   and use a YANG 1.1 must() restriction as discussed by
>> Martin and
>>      > > >     >>   Lada.
>>      > > >     >>   3. Augment the container one level up from the list
>> for
>>      > > singleton
>>      > > >     >>   protocols (suggested by Xufeng).
>>      > > >
>>      > > >     > But I think there was also a proposal to require the
>> single
>>      > > instance
>>      > > >     > to have a well-known name - but maybe this proposal is
>> no longer on
>>      > > >     > the table.
>>      > > >
>>      > > >     I actually liked this solution; however, instead of
>> picking an
>>      > > arbitrary "well-
>>      > > > known" value for name, I would specify the 0 length string
>> instead. I
>>      > > think that
>>      > > > reinforces the idea that this isn't actually a named instance.
>> :)
>>      > > >
>>      > > >        augment "/rt:routing/rt:control-plane-protocols/"
>>      > > >              + "rt:control-plane-protocol" {
>>      > > >           when "derived-from-or-self(rt:type, 'msdp:msdp') and
>> rt:name =
>>      > > ''"  {
>>      > > >           container msdp {
>>      > > >
>>      > > > One benefit of this solution is that it solves Xufeng's issue
>> of what
>>      > > the client uses
>>      > > > as the instance name.
>>      > > >
>>      > > >
>>      > > >     Thanks,
>>      > > >     Chris.
>>      > > >
>>      > > >     >
>>      > > >     >
>>      > > >     > /martin
>>      > > >     >
>>      > > >     >
>>      > > >     >> and #3. For #3, one determent would be that the control
>> plane
>>      > > protocols
>>      > > > are in a location other than where they were originally
>> envisioned and I
>>      > > don't
>>      > > > relish pulling RFC8022BIS off the RFC queue to document.
>>      > > >     >>
>>      > > >     >> Thanks,
>>      > > >     >> Acee
>>      > > >     >>
>>      > > >     >> On 2/15/18, 8:39 AM, "Reshad Rahman (rrahman)" <
>> [e-mail]
>>      > > >
>>      > > > wrote:
>>      > > >     >>
>>      > > >     >>     Hi Xufeng,
>>      > > >     >>
>>      > > >     >>     I think the intent of 8022bis was to have all
>> protocols under
>>      > > > /rt:routing/rt:control-plane-protocols/rt:control-plane-protocol.
>> I
>>      > > agree that
>>      > > > forcing a name for a single-instance is cumbersome, but I
>> think it is
>>      > > too late to
>>      > > > change tree hierachy organization at this point.
>>      > > >     >>
>>      > > >     >>     I will defer to other YDs and 8022bis authors on
>> this.
>>      > > >     >>
>>      > > >     >>     Regards,
>>      > > >     >>     Reshad.
>>      > > >     >>
>>      > > >     >>     On 2018-02-08, 9:48 AM, "Xufeng Liu" <
>> [e-mail]>
>>      > > wrote:
>>      > > >     >>
>>      > > >     >>         Hi All,
>>      > > >     >>
>>      > > >     >>         I feel that such a solution is still not clean
>> enough to
>>      > > outweigh the
>>      > > > simple augmentation to "/rt:routing/rt:control-plane-
>> protocols/".
>>      > > >     >>
>>      > > >     >>         Some considerations are:
>>      > > >     >>
>>      > > >     >>         - Name management: Neither the operator nor the
>>      > > implementation
>>      > > > wants to deal with the artificial name, whether it is
>> hardcoded,
>>      > > user-configured,
>>      > > > or system-generated. When we implement such singleton
>> protocol, we don't
>>      > > > save a name anywhere.
>>      > > >     >>         - The complexity of validation: The "when"
>> statement is an
>>      > > > unnecessary expense to the user and to the implementation,
>> especially if
>>      > > we
>>      > > > need to check all instances.
>>      > > >     >>         - Data tree query: If the singleton "MSDP" is
>> mixed with
>>      > > other protocol
>>      > > > instances, it is less obvious or harder to search for.
>> Depending on the
>>      > > > implementation, it would be worse if the entire list needs to
>> be
>>      > > iterated.
>>      > > >     >>         - Tree hierarchy  organization: I don't see too
>> big a
>>      > > problem with "all
>>      > > > single-instance protocols under /rt:routing/rt:control-plane-p
>> rotocols
>>      > > and all
>>      > > > the multi-instance ones under /rt:routing/rt:control-plane-
>>      > > protocols/rt:control-
>>      > > > plane-protocol". If necessary, some of the names can be
>> adjusted.
>>      > > >     >>
>>      > > >     >>         Thanks,
>>      > > >     >>         - Xufeng
>>      > > >     >>
>>      > > >     >>
>>      > > >     >>         > -----Original Message-----
>>      > > >     >>         > From: Reshad Rahman (rrahman) [mailto:
>> [e-mail]
>>      > > ]
>>      > > >     >>         > Sent: Thursday, February 8, 2018 9:41 AM
>>      > > >     >>         > To: Ladislav Lhotka <[e-mail]>; Martin
>> Bjorklund
>>      > > <mbj@tail-
>>      > > > f.com>;
>>      > > >     >>         > Acee Lindem (acee) <[e-mail]>
>>      > > >     >>         > Cc: [e-mail];
>> [e-mail];
>>      > > Xufeng Liu
>>      > > >     >>         > <[e-mail]>
>>      > > >     >>         > Subject: Re: [yang-doctors] How to restrict
>> to have
>>      > > single control-
>>      > > > plane-
>>      > > >     >>         > protocol instance
>>      > > >     >>         >
>>      > > >     >>         > Thanks for the suggestions. I agree that
>> hard-coding
>>      > > the name is a
>>      > > > bad idea,
>>      > > >     >>         > glad that a cleaner way of doing this is
>> possible.
>>      > > >     >>         > - We can move the must statement up to
>> restrict max of
>>      > > 1 control-
>>      > > > plane-
>>      > > >     >>         > protocol instance of type msdp?
>>      > > >     >>         > - Acee/Lada, should a note be added to
>> section 5.3 of
>>      > > 8022bis
>>      > > > regarding how
>>      > > >     >>         > to enforce single instance? How much of a
>> concern is the
>>      > > > performance
>>      > > >     >>         > impact in this specific case?
>>      > > >     >>         >
>>      > > >     >>         > Regards,
>>      > > >     >>         > Reshad.
>>      > > >     >>         >
>>      > > >     >>         > On 2018-02-08, 7:02 AM, "Ladislav Lhotka" <
>>      > > [e-mail]> wrote:
>>      > > >     >>         >
>>      > > >     >>         >     On Thu, 2018-02-08 at 12:39 +0100, Martin
>> Bjorklund
>>      > > wrote:
>>      > > >     >>         >     > "Acee Lindem (acee)" <[e-mail]>
>> wrote:
>>      > > >     >>         >     > > Hi Lada,
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > > On 2/8/18, 4:42 AM, "yang-doctors on
>> behalf of
>>      > > Ladislav
>>      > > > Lhotka"
>>      > > >     >>         > <yang-docto
>>      > > >     >>         >     > [e-mail] on behalf of
>> [e-mail]>
>>      > > wrote:
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     On Thu, 2018-02-08 at 09:20
>> +0100, Martin
>>      > > Bjorklund wrote:
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > Hi,
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > "Reshad Rahman (rrahman)" <
>>      > > [e-mail]> wrote:
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Hi YDs,
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > MSDP YANG authors want to
>> enforce
>>      > > single-instance of
>>      > > > MSDP
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > control-plane protocol. The
>> when
>>      > > “rt:type =
>>      > > > ‘msdp’“ allows
>>      > > >     >>         > multiple
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > control-pane-protocol
>> instances as long
>>      > > as they have
>>      > > > different
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > rt:name. The only workaround
>> I thought
>>      > > of is to have a
>>      > > > when
>>      > > >     >>         >     > statement
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > on the name in the top level
>> container..
>>      > > This would still
>>      > > > multiple
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > control-plane-protocol
>> instance of type
>>      > > msdp but
>>      > > > restricts the
>>      > > >     >>         > name
>>      > > >     >>         >     > to
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > a fixed name (msdp-protocol
>> in this
>>      > > case) for the top level
>>      > > > msdp
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > container to exist. Any
>> suggestions on
>>      > > how to do this
>>      > > > better?
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > Hard-coding a name like this is
>> IMO a bad
>>      > > idea.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > Better would be to simply state
>> in text
>>      > > that there MUST
>>      > > > only be one
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > instance of this type.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > But you can also add a must
>> statement
>>      > > that enforces this:
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >    augment
>> "/rt:routing/rt:control-plane-
>>      > > protocols/"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >          +
>> "rt:control-plane-protocol" {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >       when
>> 'derived-from-or-self(rt:type,
>>      > > "msdp:msdp"'  {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >      container msdp {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >        must
>> 'count(/rt:routing/rt:control-
>>      > > plane-protocols/'
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >           + '
>>      > > rt:control-plane-protocol['
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >           + '
>>      > > derived-from-or-sel(../rt:type, "msdp:msdp")])
>>      > > > <=
>>      > > >     >>         >     > 1'";
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > In general, you should be
>> careful with
>>      > > the usage of "count",
>>      > > > since it
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > will loop through *all*
>> instances in the
>>      > > list every time.  If
>>      > > > the list
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > is big, this can have a
>> performance
>>      > > impact.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     Instead of count(), it is
>> possible to use
>>      > > the so-called
>>      > > > Muenchian
>>      > > >     >>         >     > method:
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >         container msdp {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >           must
>> "not(../preceding-sibling::rt:
>>      > > control-plane-
>>      > > > protocol["
>>      > > >     >>         >     >
>>      > > >     >>         >     > >              +
>> "derived-from-or-self(rt:type,
>>      > > 'msdp:msdp')])";
>>      > > >     >>         >     >
>>      > > >     >>         >     > >           ..
>>      > > >     >>         >     >
>>      > > >     >>         >     > >         }
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     It basically states that the
>>      > > control-plane-protocol containing
>>      > > > the
>>      > > >     >>         >     > "msdp"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     container must not be preceded
>> with a
>>      > > control-plane-
>>      > > > protocol entry
>>      > > >     >>         > of
>>      > > >     >>         >     > the
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     msdp:msdp type (or derived).
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > > This looks like an elegant solution.
>>      > > >     >>         >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > "elegant" as in "less obvious" ;)  It
>> has the
>>      > > same time complexity
>>      > > > as
>>      > > >     >>         >     > the count() solution.
>>      > > >     >>         >
>>      > > >     >>         >     It should be faster on the average - it
>> has to scan
>>      > > only preceding
>>      > > > siblings of
>>      > > >     >>         >     the MSDP protocol instance whereas
>> count() always
>>      > > has to check
>>      > > > *all*
>>      > > >     >>         > protocol
>>      > > >     >>         >     instances.
>>      > > >     >>         >
>>      > > >     >>         >     It is true though that in XSLT this
>> technique can
>>      > > be made
>>      > > > considerably
>>      > > >     >>         > more
>>      > > >     >>         >     efficient by using indexed keys.
>>      > > >     >>         >
>>      > > >     >>         >     Lada
>>      > > >     >>         >
>>      > > >     >>         >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > However, since the key for the
>>      > > control-plane-protocol  list is
>>      > > > "type
>>      > > >     >>         >     > name", won't it only work if the
>> previous sibling
>>      > > has a  "name"
>>      > > > that
>>      > > >     >>         >     > is precedes the one being added?
>>      > > >     >>         >     >
>>      > > >     >>         >     > For each list entry that has this
>> container, the
>>      > > expression is
>>      > > >     >>         >     > evaluated.  It will scan all preceding
>> entries
>>      > > and ensure that there
>>      > > >     >>         >     > are none with this type.  So the order
>> of the
>>      > > entries doesn't
>>      > > > matter;
>>      > > >     >>         >     > if there are two with the same type,
>> one of them
>>      > > has to be
>>      > > > before the
>>      > > >     >>         >     > other.
>>      > > >     >>         >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > /martin
>>      > > >     >>         >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > > Thanks,
>>      > > >     >>         >     >
>>      > > >     >>         >     > > Acee
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     Lada
>>      > > >     >>         >     >
>>      > > >     >>         >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > Also note that I use
>> derived-from-or-self
>>      > > instead of equality
>>      > > > for the
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > identity.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > /martin
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Regards,
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Reshad.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >   augment
>> "/rt:routing/rt:control-plane-
>>      > > protocols/"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >         +
>> "rt:control-plane-protocol" {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >      when "rt:type = ‘msdp’"
>> {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >       description
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >         "….”;
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >     }
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >     description "….";
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >     container msdp {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >       when "../rt:name =
>>      > > ‘msdp-protocol’"  {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >         description
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >           "….";
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >       }
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >       description "MSDP top
>> level
>>      > > container.";
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > From: "Reshad Rahman
>> (rrahman)" <
>>      > > [e-mail]>
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Date: Monday, February 5,
>> 2018 at 6:25
>>      > > PM
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > To: Xufeng Liu <
>> [e-mail]>,
>>      > > >     >>         > "[e-mail]"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <[e-mail]>
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Cc: "[e-mail]" <
>>      > > [e-mail]>,
>>      > > > "Mahesh
>>      > > >     >>         > Sivakumar
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > (masivaku)" <
>> [e-mail]>,
>>      > > > "[e-mail]"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <[e-mail]>,
>>      > > > "[e-mail]"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <
>> [e-mail]>,
>>      > > > "[e-mail]"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <[e-mail]>, "
>>      > > [e-mail]"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <[e-mail]>,
>>      > > "tanmoy.kundu@alcatel-
>>      > > >     >>         > lucent.com"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <
>> [e-mail]>,
>>      > > >     >>         > "[e-mail]"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > <[e-mail]>,
>> "Acee
>>      > > Lindem (acee)"
>>      > > >     >>         > <[e-mail]>
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Subject: Re: Hi all, about the
>>      > > modification of MSDP YANG
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Hi Sandy and Xufeng,
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > I understand that you want
>> only 1 MSDP
>>      > > instance but I
>>      > > > don’t think
>>      > > >     >>         >     > that
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > justifies
>> /rt:routing/rt:control-plane-protocols.
>>      > > If we do
>>      > > > that we
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > will end up with all
>> single-instance
>>      > > protocols under
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > /rt:routing/rt:control-plane-p
>> rotocols
>>      > > and all the multi-
>>      > > > instance
>>      > > >     >>         >     > ones
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > under
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > /rt:routing/rt:control-plane-
>>      > > protocols/rt:control-plane-
>>      > > > protocol.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > I am not sure what’s the best
>> way to
>>      > > enforce single-
>>      > > > instance, I can
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > check with the other YDs on
>> this topic..
>>      > > One way it can be
>>      > > > done is
>>      > > >     >>         > as
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > follows (I’ve added the when
>> statement
>>      > > in bold to
>>      > > > existing BFD
>>      > > >     >>         >     > model),
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > it enforces that the protocol
>> name is
>>      > > ‘bfdv1’. So multiple
>>      > > >     >>         > instances
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > with rt:type=bfd-types:bfdv1
>> could be
>>      > > created, but only
>>      > > > one of
>>      > > >     >>         > these
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > instances can have the bfd
>> container.
>>      > > This is probably not
>>      > > > the
>>      > > >     >>         > best
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > way but the point is that IMO
>> protocols
>>      > > have to go under
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > /rt:routing/rt:control-plane-
>>      > > protocols/rt:control-plane-
>>      > > > protocol.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Regards,
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > > Reshad.
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >   augment
>> "/rt:routing/rt:control-plane-
>>      > > protocols/"
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >         +
>> "rt:control-plane-protocol" {
>>      > > >     >>         >     >
>>      > > >     >>         >     > >     > >      when "rt:type =
>
>