Re: [Isis-wg] [Bier] BAR field length in draft-ietf-bier-isis-extensions and draft-ietf-bier-ospf-extensions

Alia Atlas <akatlas@gmail.com> Tue, 20 February 2018 03:11 UTC

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From: Alia Atlas <akatlas@gmail.com>
Date: Mon, 19 Feb 2018 22:11:47 -0500
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To: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
Cc: Tony Przygienda <tonysietf@gmail.com>, "Dolganow, Andrew (Nokia - SG/Singapore)" <andrew.dolganow@nokia.com>, BIER WG <bier@ietf.org>, IJsbrand Wijnands <ice@cisco.com>, "isis-wg@ietf.org list" <isis-wg@ietf.org>
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Subject: Re: [Isis-wg] [Bier] BAR field length in draft-ietf-bier-isis-extensions and draft-ietf-bier-ospf-extensions
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Les,

On Mon, Feb 19, 2018 at 9:32 PM, Les Ginsberg (ginsberg) <ginsberg@cisco.com
> wrote:

> I am very sympathetic to doing “as little as possible” given we are
> talking about documents which are going through final reviews.
>
> At the same time, I think defining the authoritative source for algorithm
> values is important.
>
>
>
> I therefore agree w Ice – let’s keep the current 8 bit algorithm value –
> but make it clear that the identifiers come from the IGP Registry.
>

I do not hear from you or Ice a clear technical reason nor willingness to
address the concerns that I raised about the impact
on the use of BIER.

I see no technical reasons being used to recommend combining the BIER BAR
registry and the IGP Algorithms registry.

Andrew – I do not think there is agreement on what the function of a “BAR
> sub-type” is. Therefore I am not comfortable in adding it to the drafts.
>
> Certainly this may prove to be useful, but let’s add it when we know how
> it will be used and how to assign values to it. That requires more
> discussion than can reasonably be had in the current context.
>
>
>
> Tony / Alia – the argument that 256 algorithm values is not enough for all
> use cases (BIER specific and IGP specific and Babel specific…) – or even
> that 128 is not enough (if we allow the Flex-Algo proposal to reserve half
> of the space) – simply does not ring true to me.
>
> If I waited for  you to buy  me a beer when we reached 10 algorithms I
> likely will go thirsty for a very long time.
>

It is fascinating to see that you believe me too busy to keep up on the
side discussions happening - or perhaps merely too distracted to
recall the emails discussing acquiring half of the IGP Algorithm space for
flex-algo.  I do talk to my WG Chairs.

Please engage substantively with technical arguments.  If you have them,
you are more than capable of representing them
accurately.

So Option E seems best to me.
>

That was not part of my listed options.

Regards,
Alia


>
>    Les
>
>
>
> *From:* BIER [mailto:bier-bounces@ietf.org] *On Behalf Of *Tony Przygienda
> *Sent:* Monday, February 19, 2018 6:20 PM
> *To:* Dolganow, Andrew (Nokia - SG/Singapore) <andrew.dolganow@nokia.com>;
> *Cc:* BIER WG <bier@ietf.org>;; IJsbrand Wijnands <ice@cisco.com>;;
> isis-wg@ietf.org list <isis-wg@ietf.org>;
> *Subject:* Re: [Bier] [Isis-wg] BAR field length in draft-ietf-bier-isis-extensions
> and draft-ietf-bier-ospf-extensions
>
>
>
> My reaction to AD's options:
>
> IF you prefer or can accept the current status, but think there should be
> an IANA registry
> as is usual for managing code-points, please say so.  No more
> justification is needed.
>
>
>
>
> +1 to this option, i.e. current status with IANA BIER BAR registry.
>
> I think we have a clear and current case which is anchored already in the
> architecture RFC as section 6.9
>
> The draft https://tools.ietf.org/html/draft-zzhang-bier-algorithm-00 goes
> into more detail in this respect and I hope the draft being adopted and at
> least a single BAR value being assigned to deal with brownfield deployments
> today where not all routers support BIER.  This clearly necessitates a BIER
> BAR registry.
>
>
> IF you prefer Option B, C, and/or D, please say so with your explanation.
> More technical depth than "'we might need it" would be helpful; the
> availability of sub-TLVs already
> provides future proofing.
>
>
> +2 for Option B). Albeit we can meet future use cases with BAR subtype
> being a sub-TLV a bar type/bar subtype 16 bits field (subtype with or
> without registry and of course we can name those things differently) all
> sub-TLVs in IGPs are traditionally “optional”, i.e. adding sub-TLVs later
> _may_ cause backwards compatibility problems.  Defining the subtype today
> will allow us to specify that only type/subtype 0/0 is well defined & any
> unknown type/subtype combination must be avoided. The subtype will allow
> for BAR 0 or future BAR types to understand that subtype is in a sense a
> “mandatory sub-TLV” and the routers sending out such subtype must be
> avoided, even if the type itself is known.  Several possibilities come to
> mind immediately such as using Unicast IGP Algorithm Registry as subtype
> for certain BAR values or accommodate interesting, future work like Flex
> Algo into BIER right after IGP RFCs are available which IMO would present a
> very beneficial future direction for BIER technology cleanly governed by a
> BIER BAR registry.
>
> PS: I think we should control the urges of workgroup participants to
> explore the number of letters in the roman alphabet that we can use to
> introduce their preferred solutions if we want to get to some kind of
> consensus on this thread.
>
> PPS: Option E has been discussed in the last 16-bit thread to the point of
> logical conclusion of a "all routing protocols under the sun algorithm
> registry" and found to  be a rathole I thought ...
>
>
>
>
>
>
> On Mon, Feb 19, 2018 at 6:09 PM, Dolganow, Andrew (Nokia - SG/Singapore) <
> andrew.dolganow@nokia.com>; wrote:
>
> All,
>
>
>
> As we discussed here (as a WG) and in this topic:
>
>    - We need to have ability to define way for independent BIER
>    computation algorithms (for BIER specific computations or other use cases,
>    some of which Alia highlighted in her email below)
>    - We want to have extensibility to use other non-BIER specific
>    algorithms (as others brought up)
>
>
>
> The original draft can be argued not to provide both of those
> capabilities, and thus Option A below (marked as Current status) really
> just defers the issue. I find Option E that Ice added also
> counterproductive as it eliminates the top use case above. Thus we really
> left with options B, C, D as a compromise. From those, Option B seems to me
> the best:
>
>    - It meets the requirements above
>    - It allows a clean implementation (as opposed to Option C which is a
>    bit more kludgy). Thanks to a sub-TLV defining what BAR field carries – a
>    BIER-specific algorithm defined in BIER specific registry (a registry that
>    should be BIER specific, regardless of IGP used), or something else to meet
>    needs expressed by others, we meet the requirements from those who wanted
>    to change the Current status
>
>
>
> Option C/D are acceptable alternatives; however, Option B seems
> technically cleanest, most flexible, and meeting all requirements.
>
>
>
> Andrew
>
>
>
>
>
> *From: *Isis-wg <isis-wg-bounces@ietf.org>; on behalf of Alia Atlas <
> akatlas@gmail.com>;
> *Date: *Tuesday, February 20, 2018 at 12:05 PM
> *To: *"(Ice) IJsbrand Wijnands" <ice@cisco.com>;
> *Cc: *BIER WG <bier@ietf.org>;, "isis-wg@ietf.org list" <isis-wg@ietf.org>;
> *Subject: *Re: [Isis-wg] [Bier] BAR field length in draft-ietf-bier-isis-extensions
> and draft-ietf-bier-ospf-extensions
>
>
>
> Ice,
>
>
>
> On Mon, Feb 19, 2018 at 7:57 PM, IJsbrand Wijnands <ice@cisco.com>; wrote:
>
> Alia,
>
>
>
> I appreciate that you have finally decided to discuss this on the BIER
> mailing list.
>
>
> I know that there are individual drafts draft-ppsenak-ospf-sr-flex-algo-00
>  and  draft-hegdeppsenak-isis-sr-flex-algo-02.
> I see a bit of discussion on the is-is mailing list and at IETF 100, but,
> of course, no WG adoption.
>
> I see BIER as a fundamental technology that can be used in different
> situations.  For instance, there is not merely
> discussion of how Babel and BIER could interact - but actual code (thanks
> Sandy!); of course, that is not a WG-adopted
> draft yet either, so this is merely a thought experiment example.  How do
> the different algorithms
> work for an IGP that isn't link-state?   What about the ideas around using
> BIER with caches?  Are there issues there?
> What about algorithms that make sense for BIER or multicast - but not for
> unicast?
>
> IANA registries are not price prohibitive.  Why would we tie BIER to the
> link-state IGP registry?
>
>
>
> We are talking about what needs to be advertised in OSPF and ISIS in order
> to select the BIER underlay. We are not discussing Babel or any other
> candidate underlay technologies for BIER. Moreover, we are not limiting any
> new innovation with BIER regarding the underlay. This discussion is
> strictly related to the drafts in the title.
>
>
>
> I do not hear you making a technical argument.
>
>
>
> This is an architectural argument!
>
>
>
> An architectural argument can't also limit itself to the drafts in the
> title.
>
>
>
> If it sounded like the IANA registry was suggested as separate for BIER
> OSPF  and BIER ISIS, then your attempt to reframe the conversation might be
> reasonable.  Let me clarify - I see no current reason for an OSPF BAR
> registry and an ISIS BAR registry; it would just be a BAR registry.  Perhaps
>
> that clarification is a good reason to get the IANA registry included in
> the next update?
>
>
>
> The routing layer is separate from the BIER layer.  The BAR is for the
> BIER layer.
>
>
>
> Regards,
>
> Alia
>
>
>
>
>
> Hope this clarifies,
>
>
>
> Thx,
>
>
>
> Ice.
>
>
>
>
> Regards,
> Alia
>
>
> On Mon, Feb 19, 2018 at 7:03 PM, IJsbrand Wijnands <ice@cisco.com>; wrote:
> Hi Alia,
>
> There is one more option that I think is not fully covered from the choice
> of options related to getting a registry.
>
> The topic of the discussion is what information we need to pass in the IGP
> in order for BIER to select the correct underlay. What identifies the
> underlay is really what ever information is needed to select the Table
> (MT-ID) and Algorithm. An example of Algorithm work that is going on is
> Flex-Algo. My preferred option is to align with what ever the IGPs are
> using to identify the Algorithm.
>
> Option E: Change BAR into “IGP Algorithm” registry as documented in
> https://www.iana.org/assignments/igp-parameters/igp-parameters.xhtml#igp-
> algorithm-types
>
> Thx,
>
> Ice.
>
> On 19 Feb 2018, at 13:51, Alia Atlas <akatlas@gmail.com>; wrote:
>
> As the Sponsoring AD for draft-ietf-bier-isis-extensions-07 and
> draft-ietf-bier-ospf-extensions-12, I have been following the discussion
> on the mailing list with interest.
>
> I have not seen clear consensus for any change.
>
> Let me be clear on what I see the options are from the discussion.  Then
> I'll elaborate
> a bit on how you can express your perspective most usefully.
>
> 1) Current Status:  Bier Algorithm (BAR) field is 8 bits.  Currently, only
> value 0 is specified.  The drafts do not have an IANA registry - with the
> expectation that one will be created when the first additional use is
> clear.  It is possible that there will be objections from the IESG to
> progressing without an IANA registry.  Given the lack of clarity for future
> use-cases and after discussion, I decided not to force one after my AD
> review - but I will not push back against having a BIER IANA registry if
> raised by others.
>
> 2) Option B:  Add a BAR sub-type of 8 bits.  This would modify the current
> TLVs.
>    Define an IANA registry for the BAR type.  The meaning of the BAR
> sub-type derives
>    from the BAR type.   We can debate over the registration policy for the
> BAR type.
>
> 3) Option C: Change the BAR field to be 16 bits and define an IANA
> registry.  Part of the range can be FCFS with Expert Review, part can be
> Specification Required, and part can be IETF Consensus.
>
> 4) Option D: At some point in the future, if there is an actual understood
> and documented need, a BAR sub-type could be added a sub-TLV.  The length
> of the BAR sub-type could be determined when the sub-TLV is defined.
>
> Given
>
>   a) option D exists
>   b) there is currently only one defined value for BAR
>   c) I do not see strong consensus for change to one particular other
> option
>
> I see no current reason for a change and I certainly see absolutely no
> reason for
> a delay in progressing the documents.
>
> I do want to be clear about what the WG wants to do on this issue.
> Therefore, here is
> my following request.
>
> Please send your feedback to the mailing list as follows:
>
> IF you prefer or can accept the current status, please say so.  No more
> justification
> or reasoning is required. I just don't want the bulk of folks who are
> content to be
> overlooked by those suggesting change.
>
> IF you prefer or can accept the current status, but think there should be
> an IANA registry
> as is usual for managing code-points, please say so.  No more
> justification is needed.
>
> IF you prefer Option B, C, and/or D, please say so with your explanation.
> More technical depth than "'we might need it" would be helpful; the
> availability of sub-TLVs already
> provides future proofing.
>
> IF you have a clear technical objection to why the Current Status is not
> acceptable,
> please express that - with clear details.
>
> IF you feel that additional code-points should be allocated in a BAR IANA
> Registry or
> have thoughts on the appropriate policy, please say so with your
> explanation for what
> those should be.
>
> Unless I see clear and strong consensus for something other than the
> Current Status,
> that will remain.
>
> IF there is clear and strong consensus for Option B, C, or D, or adding an
> IANA registry with particular values, then it will be possible to have a
> change up through this Weds night - with a 1 week WGLC on that particular
> technical change.
>
> My priority is to have the base BIER specifications published as Proposed
> Standards so that more BIER implementations and deployment can be done.  I
> would like the WG to wrap up the core work (as expressed in the proposed
> recharter) so that you all can look
> at how to use it.
>
> Given this topic was raised last Weds and given that there are no
> technical objections raised to the documents as are, there isn't much time
> - so please just respond to this email ASAP.  My deadline for a decision is
> 6pm EST on Weds.
>
> Regards,
> Alia
>
> _______________________________________________
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