Re: [Bier] WGLC - draft-ietf-bier-te-arch 1 WEEK

["BRUNGARD, DEBORAH A" <[e-mail]>]

Toerless,

A couple of high level comments:

I've seen you mention 5-years lifetime of the draft a couple of times as rationalization not to change. Publication is not based on lifetime of a draft. Authors/WG need to be open to change especially during WG last call (when collaborating with other working groups in an Area and the document has not been shared over "lifetime"), IETF Last Call (especially other Area Directorate reviews), and, of course, IESG review. As you have been an author many times, I think you are very familiar with the churn. I just want to remind for the benefit of others as I've seen many new authors frustrated when their document becomes a working group document and there is churn.

It's always difficult to interpret personal comments over email - even those meant with the best intention or to amuse. Best is to keep to technical discussion. E.g. comments such as " but given those and other (below) realities i hope it is not too rude for me to say that its perceived on my end a bit more like selective hazing" and " to the mail you sopposedly sent" may be interpreted very differently by the intended person or others on the mailing list than what you meant. As I was doing this email, I see you already responded to Lou explaining. For me, "selective hazing" is a rather strong reaction to someone commenting. We want to encourage folks to comment, not discourage. And it's not to you, it's the document. We all have different styles of writing, but on the lists, best is to keep it technical.

On the document:

As you say yourself, current abbreviations are overloaded. Which is why when new ones are proposed, the preference is to not keep overloading (in this case, "PE") if more accurate abbreviations can be identified. This document is defining replication and forwarding based on a precalculated path. I was not questioning the use of the term "engineering" for something other than TE, I was questioning the naming of this BIER mechanism as "engineering". I haven't seen replication/forwarding referred to as "engineering". If you and the working group think the best name is "engineering" - let it stand for now. Most important for me (as AD for TEAS) was that you removed "TE" as that was inaccurate. Again, just because it has been 5 years, now is the time to improve, once a document is published, it is for a lifetime. I just noted your email asking input on the naming - thanks - that's good - we can see what folks think.

Your suggested revision for the sentence comparing with RSVP-TE is much better.

I understand when you use the term controller, it is not necessarily a PCE. What I was asking (especially as an operator) was to include in the abstract and intro sentences on the difference of BIER and BIER-PE. This sentence in section 1.3 "BIER-PE replaces in-network autonomous path calculation by explicit paths calculated off-path by the BIER-PE Controller" would be very helpful in understanding the technology earlier in the document. In the abstract, suggest a sentence "BIER-PE differs from BIER in the use of explicit paths calculated off-path by a controller."

A new comment - if you intend this mechanism to be supported by BIER hardware (section 3.2) - you probably want to get support for this document to be an update of RFC8279?

Thanks,
Deborah


-----Original Message-----
From: Toerless Eckert <[e-mail]> 
Sent: Thursday, February 27, 2020 3:36 AM
To: BRUNGARD, DEBORAH A <[e-mail]>
Cc: Lou Berger <[e-mail]>; [e-mail]; [e-mail]; Jeffrey (Zhaohui) Zhang <zzhang=[e-mail]>
Subject: Re: [Bier] WGLC - draft-ietf-bier-te-arch 1 WEEK


Hi Deborah,

inline

On Wed, Feb 26, 2020 at 09:33:17PM +0000, BRUNGARD, DEBORAH A wrote:
> Hi Toerless,
> 
> Your comment:
> > > I would appreciate if you could try to partition your opinions into
> > > things you think MUST be solved before passing the document to IESG (for
> > > IETF/IESG review) and those issues that could then be solved when it is
> > > in IETF/IESG review. For example, i think a final choice of name could
> > > be something that shouldn't block the document to take this step.
> > >
> 
> Waiting for the IESG to "name" your technology will definitely result in a much longer delay than sorting out in WG Last Call.

Ack

> You noted, you had presented an earlier version of this document in TEAS, but it is at the time of WG Last Call (per the charter), the TEAS/MPLS/and probably PCE, should have been notified (I included MPLS as you have multiple proposals on use of MPLS labels). I've contacted your BIER Chairs/AD to extend at least a week the Last Call.

Thanks. I hope that feedback would still have to go all go to BIER, and
not to those other WG mailing lists, right ? Don't want to hunt feedback
across many WG lists. 

> On naming, as Lou noted, preference is to align terminology used in other working groups - especially within the routing area. The RFC-editor also recommends careful use of abbreviations - it is expected new abbreviations are added to a list:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.rfc-2Deditor.org_materials_abbrev.expansion.txt&d=DwIDAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=yX_6NAhGb01k0I5mGk47ecTvjnxrstlW9R1Vjdlxy_Y&s=MqqVe6A0srzY2l9XMurr7U__uZcGjMjqTWAw6bMDew8&e= 

See below

> As you can see, PE is already used.

a) 461 out of 2651 abbreviations in that doc are overloaded.

b) There is no indication that suffixes of a composite abbreviation have to be unique.

c) We would only want to use BIER-PE as an abbreviation, not PE alone.

   That is btw. why i changed all the occurances of "path engineering" in
   the text to explanatory "steering" or "policy" and only use BIER-PE as a name.

d) Of course i would get BIER-PE registered when being in RFC-editor
   state like i have done in the past in other RFCs.

e) How about SR first meaning Source Routing and then being
   overloaded with Segment Routing ? And if Segment Routing
   was a valid new term (as it has more flexibility than
   Source Routing), why then not allow Path Engineering as
   a new term for us ?
   
e) SR in abbrv.expansion.txt:

   SR         - sender report (SR)
   No "Source Routing", "Segment Routing", no SR-MPLS,
   No SRH from RFC6554, No consideration for disambiguating
   RFC6554 SRH from SRv6 SRH, ... NADA! (not even NADA/RFC8698)

I know your and Lou's comments wrt. naming are well meaning,
but given those and other (below) realities i hope it is not too rude for
me to say that its perceived on my end a bit more like selective hazing.

Can we please turn this around and you help us in actually selecting a good name ?

> And in the Routing Area, for our PE abbreviation, we could say it should have an asterisk????

Sure, please talk with RFC editor to get it added to the doc.

But asterix does not say anything about whether or not there
is a conflict when reusing another abbreviation in a suffix
of a longer name. Maybe when you get the asterisk, ask the RFC
editor about that. There are no prior cases of this in the
doc, so not possible to derive case law from the existing abbreviations.

>Your justification is that "PE" is short similar to "TE", but for the Routing Area, it needs to be either different or maybe add a letter (three letters). If you look thru the list, that's what others have done e.g. in SPRING, they have a new document also using "PE" differently but it's abbreviated "EPE".

[ SPRING is the WG working on sender report (SR) ?  (sorry, could not resist) ]

draft-ietf-spring-segment-routing-central-epe - "Egres Peer Engineering"

To me its primarily a good reference that other work is not contested
when combining the word engineering with other words beside "Traffic"
whereas this is contested when i am prosing to do it for the BIER work.

> As we all enjoy trying to name "something",

Not when the baby has a name for 5 years and that then gets contested.

> I checked PCE documents (as you noted in the document, BIER-PE requires SDN/PCE controller).

BIER-PE does not require a PCE according to RFC 4655, RFC 4657. That is
a highly desirable option when you want to use BIER-PE for Traffic Engineering,
but it is explicitly not scoped in this document so as to not encumber
the document or constrain the applicability of its technology.

The document has early on in section 2 the mandatory dependencies
of BIER-PE, which includes the "BIER-PE Controller" as a concept
as abstract as possible, and the document does explain what that
BIER-TE controller needs to do without expecting any PCE arch
TE definition . Such a BIER-PE controller could in one instance
be an operator using CLI.

I had another explanation in section 1.1 i added/proposed for Lou,
stating how the "BIER-PE controller" would be a new function within
a larger PCE if BIER-PE was used in a traffic engineering / PCE
framework, but Lou said i should rather remove that section 1.1,
which i did, so i think he is fine with waiting for the BIER-TE
framework draft to define how the BIER-PE controller relates to a PCE.

> As Lou says - there is no mention of "path engineering" either in PCE documents or any IETF documents. So maybe "PE" in the string is not the best.

There was also no mention in IETF or PCE documents of "Segment Routing"
before it was invented, and SR likely meant something else, so what is the point ?

>My 2-cents, how about "SREP-BIER" (Source Routed Engineered Path)?

See above on the SR confusion. Also note that the bigger common
technology here is not 'source routing', but BIER, so that should be the prefix.

Also, see below.

> Have fun naming.

See above. 

> but please stabilize on a name before hand-off to the IESG - otherwise the IESG will have all the fun.

What would really help the authors and the WG to finalize on a name 
would be for you and Lou go beyond explaining what we should NOT choose
as a name to what we are allowed to choose as names. Otherwise
we could as well have the poor WG circle around this block multiple time.

So please with sugar and whipped creme topping, let us know
what will be permitted.  Lou said we should re-use existing terms,
i told him why using ONLY those would not well represent the
unique novelty of BIER-PE but lead to confusion with unicast
semantics (and besides: see SR and anybody else choosing new names
for equal good reasons).

BIER-PE is an easy compromise that i think makes everybody
equally but only little unhappy. If not then then please
comment on the following list which i hope would be 
sufficiently broad for the WG to select a name from:

BIER-ET  - Explicit Trees
BIER-EET - Explicit Engineered Trees
BIER-BET - Bit Engineered Trees
BIER-BST - Bit Steered Trees
BIER-TrE - Tree engineering     
BIER-ET  - Engineered Trees
BIER-ST  - Steered Trees

BIER-ASB - Adjacency Steering Bits   (adjacencies are how bits in BIER-PE are defined)
BIER-AB  - Adjacency Bits  
BIER-SB  - Steering Bits             (overloads with "Source Block" - never heard)

[ I prefer terms with Tree, because thats the unique distinction
  to paths, and highlight the multicast specific characteristic. ]

> As BIER-PE requires use of an SDN/PCE controller - here's my early AD comments - please mention this earlier in the document - abstract, intro. e.g. the SPRING document has as the title "centralized" EPE.

I answered this alredy above.

> "SR aims to enable lightweight path steering via loose source routing. Compared to its more heavy-weight predecessor RSVP-TE, SR does for example not require per-path signaling to each of these hops."
> 
> RSVP-TE provides very different capabilities than SR and BIER. With RSVP-TE glasses on, one could say SR and BIER provide very limited capabilities.  And both SR and BIER require very heavy-weight SDN controllers. So it just depends where the operator/vendor wants to put their "weight". 

> But it's not for IETF to do the judgement.
> An RFC is not for marketing one technology vs. another.

The goal of the text was not to make non-technical judgements about the overall TE
systems or to market SR, but simply to provide a technical explanation of
the aspects of SR that relate to BIER-PE and relate that to RSVP-TE given
how RSVP-TE/P2MP is also the equivalent alternative for BIER-PE:

  SR : RSVP-TE   ~=   BIER-TE : RSVP-TE/P2MP

But:
"predecessor" is an imprecise qualification. I just thought
about the timeline, not the possible misinterpretation that SR
would/could/should 1:1 superceed RSVP-TE. Also, the verbage of heavy 
vs. lightweight is not correctly constrained to the technical
point of comparison (on-transit-hop heavyness of path steering).

I propose to change that sentence accordingly:

"SR supports through the use of source-routing strict and loose hop path steering across transit hops that is lightweight on those transit hops because it does not require per-hop/per-flow signaling to and forwarding plane state on those transit hops. In comparison, RSVP-TE and RSVP-TE/P2MP do require such per-hop/per-flow transit-hop signaling and forwarding plane state "

I think this is now technically precise and limited to the necessary
comparison in this context. If you still have concerns,
pls. let me know why, ideally with proposed text that would solve
those concerns. I think it is important to explain the
relevant technical aspects that where the core reasons for doing
BIER-PE, especially in comparison to existing solutions.

[ Btw: If memory serves me well, the whole PCE architecture was introduced first
  by recognizing that you could not use RSVP-TE in situations with
  multi-headend resource contention without a central/coordinated PCE
  efficiently, and then implementations managed to build those PCE fairly
  lightweight into headend routers. Technically i would therefore disagree
  with your contentions that PCE need to be very heavy-weight and that
  RSVP wouldn't need them but only SR/BIER-PE. But definitely this
  BIER-PE document is not the place to have that argument. A later BIER-TE framework
  document nevertheless would IMHO be more useful to adopters and operators
  if it had such technical description - without judgement and marketing,
  just the facts! ]

> Hopefully my working groups (TEAS, MPLS, PCE) are given the "heads-up" soon - I'd prefer discussion during working group last call vs. IETF Last Call or my needing to enter a "Discuss" waiting for their review.

I did see Lou sending mail to TEAS and DetNet and Lea to MPLS, did you send to PCE ?. 

I do of course welcome feedback from any group, but i am not worried
about MPLS or PCE. There are no changes on the MPLS encap side, and
as explained above, mapping BIER-PE into the PCE framework is
also subject to followup work (like i think it was for SR as well).

Thanks a lot. 

Cheers
    Toerless

> Thanks!
> Deborah
> (AD hat on)
> 
> -----Original Message-----
> From: BIER <[e-mail]> On Behalf Of Toerless Eckert
> Sent: Tuesday, February 25, 2020 7:02 PM
> To: Lou Berger <[e-mail]>
> Cc: [e-mail]; [e-mail]; Jeffrey (Zhaohui) Zhang <zzhang=[e-mail]>
> Subject: Re: [Bier] WGLC - draft-ietf-bier-te-arch 1 WEEK
> 
> Lou, *:
> 
> Here is the next and hopefully final github version for your review.
> If you can give a thumbsup i will upload to datatracker,
> and the WG chairs would also be able to finalize WG last-call.
> 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__raw.githubusercontent.com_toerless_bier-2Dte-2Darch_7e996deb1dcd18596d4864c750f6e7541d737e6f_draft-2Dietf-2Dbier-2Dte-2Darch.txt&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=hbVUmt6ob-Ilgt00kiOlwAOcA68kldlxvO0Lqq-gKxo&e= 
> 
> And here the diff to -05, last version before taking input from your review into account.
> Given how 1.1 was removed, this seems like the most logical comparison point.
> 
> https://urldefense.proofpoint.com/v2/url?u=http-3A__tools.ietf.org_tools_rfcdiff_rfcdiff.pyht-3Furl1-3Dhttps-3A__tools.ietf.org_id_draft-2Dietf-2Dbier-2Dte-2Darch-2D05.txt-26url2-3Dhttps-3A__raw.githubusercontent.com_toerless_bier-2Dte-2Darch_7e996deb1dcd18596d4864c750f6e7541d737e6f_draft-2Dietf-2Dbier-2Dte-2Darch.txt&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=jTvrGagqHgPKneTUpOvNkeYcl7cxDSV32gLk--vyzdQ&e= 
> 
> Changes to -05 are now easily seen as limited textual:
> - Name change BIER-TE to BIER-PE
> - Explanations using steering/policy
> - [RFC-editor remove note] about name change.
> - BIER-TE controller host -> BIER-TE Controller (unrelated to Lou)
> 
> Detailled answers, explanations below.
> 
> Cheers
>     Toerless
> 
> On Tue, Feb 25, 2020 at 01:19:26PM -0500, Lou Berger wrote:
> > Hi Toerless,
> > 
> >     This revision will mostly remove my objection related to the use of TE
> > by the document.  I suspect in section 7.2 you have two instances where
> > "traffic" needs to be replaced with "path".
> 
> Fixed
> 
> > More substantively, I think you
> > should delete section 1.1 and leave its subject  matter  to
> > eckert-teas-bier-te-framework to be covered/worked out.  If you want to keep
> > it, I think there's a longer discussion need on its contents.
> 
> Removed section 1.1 from the text.
> 
> I have added to the beginning of 1. an [RFC-editor: pls. remove ] section
> explaining the naming change so late in the process to further IETF/IESG
> reviewers (if i had just put it into the changelog i fear it will 
> be overlooked by reviewers).
> 
> For what is worth, i did like the idea of having explanations 
> about relationship of BIER-PE to BIER-TE, especially because the
> framework is IMHO not yet in a state to serve as a good even draft
> reference (it was only pointed to in section 1.1, so also removed
> as reference).
> 
> How about this: If IESG review wants to have that type of explanation back,
> i'll knock on your door to revive and help me fix up that text.
> 
> > FWIW I still think the introduction of the a new term "Path Engineering",
> > rather than reusing one of the existing IETF terms for the same capability
> > ("routing policy", "policy based routing", "path steering") seems  likely to
> > lead to more confusion then if you stuck with an established term.  I'll
> > leave this to others to argue.
> 
> Ok, second time around you're suggesting this, i now owe you an explanation
> why i think these terms are technically misleading:
> (its a bit long, that why i avoided the explanation in before).
> 
> All the established terms you propose come from unicast and
> never had a re-definition/re-interpretation for IP multicast.
> 
> Using any of these terms in the name would easily lead to
> people (especially when not reading the doc) think the
> BIER solution here works like in both IP multicast and
> BIER in before BIER-PE: By impacting the underlying unicast
> (forward) routing (BIER) or RPF (reverse path) routing (IP Multicast). 
> 
> Examples: You can use static muRIB routes to steer traffic for
> IP Multicast or BIER. You can also use separate IGP (Flex-)topologies
> to do the same dynamically. Thats all great stuff to describe in a
> BIER-TE framework document (in conjunction with BIER), but that
> is also the stuff i do not want BIER-PE to be confused with
> because there are technical limitations to those unicast routing policy/
> steering approaches when its applied to trees:
> 
> Try to use any of the pre-existing mechanisms for unicast routing policy
> or path steering with BIER or IP multicast to build steiner trees.
> Not generally possible. With BIER-PE, no problem. Same thing with
> disjoint trees (even MRT flex-algo's wouldn't achieve the same).
> 
> IMHO, the term "Path Engineering" is free of this mis-name-recognition
> because it is a new. The name also hints at the fact that this could be
> in support of, or a component of traffic engineering. 
> And wrt to minimizing the change to the long held name,
> the hamming distance is just one character/word. So it's the
> 'safest/most-conservative/logical' name change this late in the
> process.
> 
> As i said, i would be happier with a more unique new descriptive
> name like "Tree Steering Bitstrings" (BIER-TSB), but i do not feel
> like making such a big naming change without more explicit support
> by more members of the WG this late in the process. 
> 
> > I think this covers all the detailed discussion points below. If not, can
> > you extract the ones you'd like to keep discussing?
> 
> Still sad about the missed opportunity of fixing this naming 
> problem earlier wrt. to the mail you sopposedly sent, and
> happy to beat myself up if that ended up being my fault, but
> i guess i shouldn't continue to dig into that issue if it would
> turn out to be someone else's fault.
> 
> Otherwise i am fine.
> 
> If you want to give the doc now a thumbs up in response to the last
> call, that would be great ;-)
> 
> EOF
> 
> > Thanks again for the responsiveness to my comments!
> > 
> > Lou
> > 
> > On 2/24/2020 8:57 PM, Toerless Eckert wrote:
> > > Hi Lou, round 2.
> > > 
> > > Here is the github pre-version of -07 of the draft:
> > > 
> > > https://urldefense.proofpoint.com/v2/url?u=https-3A__raw.githubusercontent.com_toerless_bier-2Dte-2Darch_62378f618299307349a934fc6ad78e1af9e16771_draft-2Dietf-2Dbier-2Dte-2Darch.txt&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=ijbHbeNowm8uYigeF3tPQBOSrFL5chyoxfjBXyDOxPg&e= 
> > > 
> > > Diff:
> > > 
> > > https://urldefense.proofpoint.com/v2/url?u=http-3A__tools.ietf.org_tools_rfcdiff_rfcdiff.pyht-3Furl1-3Dhttps-3A__tools.ietf.org_id_draft-2Dietf-2Dbier-2Dte-2Darch-2D06.txt-26url2-3Dhttps-3A__raw.githubusercontent.com_toerless_bier-2Dte-2Darch_62378f618299307349a934fc6ad78e1af9e16771_draft-2Dietf-2Dbier-2Dte-2Darch.txt&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=VMWxCE2IzT007rczFZWwh1CEB3xG48xOj5RifpjIt5s&e= 
> > > 
> > > I would appreciate if you could try to partition your opinions into
> > > things you think MUST be solved before passing the document to IESG (for
> > > IETF/IESG review) and those issues that could then be solved when it is
> > > in IETF/IESG review. For example, i think a final choice of name could
> > > be something that shouldn't block the document to take this step.
> > > 
> > > If this goes along into IETF107, it would be great if you could find the
> > > time to be at the BIER-WG meeting.
> > > 
> > > Summary of changes:
> > > 
> > > 1. Changed abbreviation BIER-TE to BIER-PE, otherwise we can not unconfuse
> > > readers of the difference between BIER-PE and BIER-TE.
> > > 
> > > Relationship: BIER-TE = (BIER with steering: BIER-PE or othre) plus resource
> > > allocation mechanisms, and this document only describes BIER-PE.
> > > 
> > > 2. Removed all use of the term "path engineering" from the (explanatory) text,
> > > replaced with path / tree steering or policy in the text (like RFC8402).
> > > 
> > > 3. In result, "Path Engineering" is now solely a name  for the mechanism.
> > > In the same way as SR introduced "Segment Routing" as a name, but explains
> > > what it does with the terms "steering" and "policy".
> > > 
> > > 4. I think a unique new term not already used in before is helpful because
> > > what BIER-PE does is quite unique and new. And reusing an existing term
> > > always brings out more people wanting to argue about the accuracy of how
> > > their pre-existing term is applied.
> > > 
> > > I hope we can have a deterministic, short latency decision mechanism for
> > > the term. After we've decided on the term, its easy to update the doc
> > > again with that new term (%s/PE/XXX/g).
> > > 
> > > I'll throw "Tree Steering Bitstrings" (BIER-TSB) into the ring.
> > > 
> > > [The main issue with name change now is that we've gotten some followup
> > > work such as YANG model that also refers to BIER-TE meaning BIER-PE, so
> > > that would also need to change name. See below for my reply to that naming
> > > change you said you suggested .]
> > > 
> > > 5. I also refined the section 1.1 that was introduced in -06 to mention
> > > e.g.: PCE.
> > > 
> > > Specific answers to the mail thread below.
> > > 
> > > Cheers
> > >      Toerless
> > > 
> > > On Fri, Feb 21, 2020 at 03:01:51PM -0500, Lou Berger wrote:
> > > > > [ Would have been nice if you could have commented a bit earlier.
> > > > >     But i can understand how a few years is not enough time ;-P
> > > > >     (actually no kidding, i really can.) ]
> > > > I raised this as an issue last march - at both the Chair and AD level..  I
> > > > thought I made the same point to you privately after one the presentations
> > > > at IETF101, but if you don't remember it, I accept that I didn't.
> > > Did you include the authors ? I could not find any email about this.
> > > Also no forwarded emails from AD/chairs i could find. If you still have
> > > a copy, pls. PM. This is annoying...
> > > 
> > > I do not remember naming issue discussed after IETF101, but i am
> > > sure i was preoccupied with technical issues and might not have
> > > given it too much thought back then. Of course there was a lot of
> > > time since IETF101 to bring up the naming point again...
> > > 
> > > > Well that document seems like a fine place to describe how BIER-RP (routing
> > > > policy) can be used to deliver BIER-TE.
> > > > 
> > > [...]
> > > > Do we really need a new term to describe here?  I find zero (0) instances of
> > > > Path Engineering in any RFC.  Routing policy (and policy-based routing) on
> > > > the other hand are fairly well established terms in the industry.  I think
> > > > this just sows seeds for future confusion on this topic.
> > > > 
> > > > Why is "routing policy" not good enough for what is being defining here?  I
> > > > again point out, this is the term being used in SPRING for basically the
> > > > equivalent function/purpose. (Yes the forwarding mechanism is different, but
> > > > the objective is not.)
> > > SPRING did establish new unique name/terminologies, like "Segment".
> > > As said above, i think its best we do the samegiven how unique this is.
> > > 
> > > Looking at rfc8402, "steering" and "policy" are used in verbal
> > > explanations, without providing specific terminology for them,
> > > so i did follow that example too.
> > > 
> > > > > but kept name BIER-TE (see below).
> > > > > 
> > > > > - Added section 1.1 explaining how BIER-TE relates to traffic
> > > > >     engineering, naming use-cases where its for example beneficial standalone and
> > > > >     and what it could be combined with for more comprehensive TE solutions,
> > > > >     but also stating that those integrations are outside the scope of this
> > > > >     document.
> > > > So this section seems to miss what has been going on in traffic engineering
> > > > / TEAS for the last 5+ years (i.e., controller-based TE approaches)
> > > I don't think that is a correct assessment. BIER-PE itself requires a
> > > controller to calculate paths / trees. With or without other traffic
> > > engineering components. That component is called the BIER-PE controller and
> > > has been in the draft forever.
> > > 
> > > The new section 1.1 added in response to your review relates that
> > > BIER-TE controller to an overall TE controller, using the PCE example
> > > and refrerence to it.
> > > 
> > > There is really nothing more that a BIER-WG document could or should
> > > do. What this document intended to support is whats necessary and
> > > sufficient to get the forwarding plane implemented/standardized.
> > > Everything else is for independent followup work in TEAS IMHO,
> > > such as reviving the framwork draft.
> > > 
> > > >    and then goes on describe path steering  in a very brief way.  I read this as
> > > > saying that BIER *could* do TE in the future and *can* support routing
> > > > policy and path steering today.
> > > Even stronger: BIER-PE is always meant to ONLY do that (steering),
> > > any additional TE functions wold come from independent other components.
> > > And simple examples for that are given in section 1.1.
> > > 
> > > > > - changed "traffic engineering" term in the whole doc to "path engineering",
> > > > >     where appropriate.
> > > > While this is appreciated, I'm not sure it's helpful.  As stated above, I
> > > > think the introduction of the new PE term is confusing as the continued use
> > > > of BIER-TE.
> > > See above. We can certainly not use "BIER-TE" to mean two different
> > > things, so i hope that concern is resolved.
> > > 
> > > > > The mayority of customers i talked to only used RSVP-TE for path
> > > > > engineering, and not for anything more. Several didn't even know it
> > > > > can do bandwidth reservation. Nobody knew it could do latency
> > > > > guarantees, because nobody knows an implementation that supports that.
> > > > > [All reasons btw. why replacing RSVP-TE with SR happened in the industry.]
> > > > While I'm going to avoid getting into product differentiators and marketing,
> > > > you're not mentioning that even those products and customers who didn't
> > > > support/use per LSP queuing, did available resource bookkeeping and even
> > > > admission control.
> > > I think the point is mood now (given how we'll change the name BIER-TE
> > > to a better term). But maybe to better explain: We started calling this
> > > TE so customers would easier understand that this is intended to give
> > > them what they actually use RSVP-TE for (Traffic Steering), and not
> > > necessarily all that RSVP-TE could do beyond that. A central controller
> > > is assumed to exist in BIER-PE too.
> > > 
> > > Given how SR also shows how you can be successful in deployment
> > > without betting on 'TE' name recognition, i have no quarrels in
> > > changing the name. As said above, its motly a question of finding
> > > the best term and changing the followup works names too.
> > > 
> > > > > In any case, the name BIER-TE was selected to reduce confusion
> > > > > with customers, not to maximize naming correctness in IETF.
> > > > umm, the IETF is a standards body not an industry marketing forum, so I'm
> > > > unclear how this point helps your argument.
> > > It's not am argument or justification, just an explanation. Not only to you,
> > > but also the WG.
> > > 
> > > >   It seems that you're saying
> > > > that if we call it BIER-TE we can market it in place of existing IETF TE
> > > > solutions - even though it doesn't yet have the TE capability covered in
> > > > draft-eckert-teas-bier-te-framework.
> > > ....
> > > 
> > > > Assuming I'm reading it right, this just confirms to me that the current
> > > > work needs to be renamed and that draft-eckert-teas-bier-te-framework will
> > > > define BIER-TE.
> > > Yes. BIER-TE could btw. rely on BIER-PE or BIER + other path steering
> > > (e.g.: flex-algos), so BIER-PE is only one option for the path-steering
> > > options for BIER-TE.
> > > 
> > > > My point wasn't that BIER=SR, but rather both deliver support for path
> > > > steering and policy based routing.
> > > Yepp, i hope we're in violent agreement.
> > > 
> > > Cheers
> > >      Toerless
> > > 
> > > > Thanks for being responsive!
> > > > 
> > > > Lou
> > > > 
> > > > > All the SR options do really require that you set up multicast trees with
> > > > > e.g.: replication-SIDs that together form the equivalent of a
> > > > > multicast tree, like you would have built with RSVP-TE. Except that
> > > > > the signaling how to build the tree is left for someone else, like
> > > > > PCECC. (AFAIK, i may not be on top of all details). In BIER-TE,
> > > > > there is no such per-tree state on transit nodes.
> > > > > 
> > > > > Instead of a 256 bit bitstring in BIER-TE think of a header with up to 256 SIDs
> > > > > (e.g.: 128 bit per SID in SRv6). That would be the SR equivalent of BIER-TE.
> > > > > Just a bit less ( ;-) ) less efficient on the wire than BIER-TE and extremely
> > > > > harder to parse.
> > > > > 
> > > > > Cheers
> > > > >       Toerless
> > > > > 
> > > > > 
> > > > > On Wed, Feb 19, 2020 at 06:38:38PM -0500, Lou Berger wrote:
> > > > > > Hi,
> > > > > > 
> > > > > >       I have no issue or objection to the mechanisms being defined in this
> > > > > > document as much as they go, but I was quite disappointed that despite the
> > > > > > name of the document and use of 'bier-te'  to see that the document doesn't
> > > > > > define any traffic engineering support, at least as far as the term has been
> > > > > > used in IETF RFCs.  In particular it totally lacks any discussion of
> > > > > > resources usage and/or allocation.  What it currently describes certainly
> > > > > > provides good and useful path/traffic steering that can be used to support
> > > > > > policy-based routing.  Basically it does the same as what is defined by
> > > > > > draft-ietf-spring-segment-routing-policy.
> > > > > > 
> > > > > > I personally (not speaking for the related WGs that I chair) would prefer to
> > > > > > see this document be revised  to include resource allocation that would
> > > > > > allow BIER-TE to support TE usage such as DetNet.  Barring such an addition,
> > > > > > I'm against publication of this document as is and I think the document
> > > > > > should be recast and renamed to be aligned with the SR example, i..e., BIER
> > > > > > routing policy (or path steering).
> > > > > > 
> > > > > > Lou
> > > > > > 
> > > > > > On 2/18/20 3:45 PM, Greg Shepherd wrote:
> > > > > > > Thanks Toerless and Jeffrey
> > > > > > > 
> > > > > > > https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-2Dbier-2Dte-2Darch_&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=jH9x7gacv335Qdcq_btgUNtO3-TQxwLspmfVzbCC9Oo&e= 
> > > > > > > 
> > > > > > > One more week of WGLC. Please read the latest rev and respond to this
> > > > > > > thread w/wo support.
> > > > > > > 
> > > > > > > Chairs
> > > > > > > (Shep)
> > > > > > > 
> > > > > > > 
> > > > > > > On Tue, Feb 18, 2020 at 12:07 PM Jeffrey (Zhaohui) Zhang
> > > > > > > <zzhang=[e-mail]
> > > > > > > <mailto:[e-mail]>> wrote:
> > > > > > > 
> > > > > > >       Hi Toerless,
> > > > > > > 
> > > > > > >       Thanks!
> > > > > > >       I support moving this to the next stage.
> > > > > > > 
> > > > > > >       Jeffrey
> > > > > > > 
> > > > > > >       On Fri, Nov 01, 2019 at 07:42:38PM +0100, Toerless Eckert wrote:
> > > > > > >       > Thanks Jeff
> > > > > > >       >
> > > > > > >       > I have now pushed out -05 with the answers and hopefully
> > > > > > >       resolution to
> > > > > > >       > your points in email below.  Biggest addition was a section about
> > > > > > >       > reuse of BPs (without DNR) which came out of the confusion i
> > > > > > >       think the
> > > > > > >       > reuse in the ECMP example raised. I was afraid so far to explan
> > > > > > >       that
> > > > > > >       > as it may not be easy to absorb and ultimately is stuff only
> > > > > > >       > controller developers need to understand, but hopefully useful.
> > > > > > >       > And then of course the summary of BP optimizatins you asked for
> > > > > > >       >
> > > > > > >       > Diff from last version i sent you:
> > > > > > >       >
> > > > > > >       >
> > > > > > >       https://urldefense.com/v3/__http://tools.ietf.org/*rfcdiff?url1=https:
> > > > > > >       > **Araw.githubusercontent.com
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__Araw.githubusercontent.com&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=xVAjp721g_El61X8yMyRw3ggZhIQ-SG9Zb-UFpVtOHw&e= >*toerless*bier-te-arch*master*draft-ietf-b
> > > > > > >       > ier-te-arch-05.1.txt&url2=http:**Atools.ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__Atools.ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=ggPrkSBziBxcUV48NKmskrw6fOzU94m3Dk5u67UMcRg&e= >*id*draft-ietf-bier-te
> > > > > > >       >
> > > > > > >       -arch-05.txt__;Ly8vLy8vLy8vLy8!!NEt6yMaO-gk!VuQCVHnqJy_aYI-FNt9A1a5EzH
> > > > > > >       > OCr0fZkLPbgg3CPNu0PyrWsrFx41_jWX2At8V-$
> > > > > > >       >
> > > > > > >       > full -04 -> 05 diff:
> > > > > > >       >
> > > > > > >       >
> > > > > > >       https://urldefense.com/v3/__http://tools.ietf.org/*rfcdiff?url1=http:*
> > > > > > >       > *Atools.ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__Atools.ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=ggPrkSBziBxcUV48NKmskrw6fOzU94m3Dk5u67UMcRg&e= >*id*draft-ietf-bier-te-arch-04.txt&url2=http:**Atools.
> > > > > > >       > ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=URRMpXM94kB4xSw27o7fG_DV2IOD4kJVE3esjPI_b9g&e= >*id*draft-ietf-bier-te-arch-05.txt__;Ly8vLy8vLy8v!!NEt6yMaO-gk
> > > > > > >       > !VuQCVHnqJy_aYI-FNt9A1a5EzHOCr0fZkLPbgg3CPNu0PyrWsrFx41_jWancpziv$
> > > > > > >       >
> > > > > > >       > Comments inline below.
> > > > > > >       >
> > > > > > >       > Cheers
> > > > > > >       >     toerless
> > > > > > >       >
> > > > > > >       > On Mon, Oct 28, 2019 at 07:52:59PM +0000, Jeffrey (Zhaohui)
> > > > > > >       Zhang wrote:
> > > > > > >       > > I Thought u-turn is the most simple comparison leaf vs.
> > > > > > >       non-leaf BFR.
> > > > > > >       > >
> > > > > > >       > > Zzh> The text in the email is seriously misaligned. Looking at
> > > > > > >       the picture in the diff link, while you gave a U-turn example,
> > > > > > >       though even if BFER2 is not connected to BFR2  but only connected
> > > > > > >       to BFER1 (hence no U-turn), then BFER1 is still not a leaf BFER I
> > > > > > >       suppose. That's why I said the first sentence of the above
> > > > > > >       paragraph is enough to define Leaf BFER while the example itself
> > > > > > >       is actually not needed.
> > > > > > >       >
> > > > > > >       > Argh... ok, had to fix two words, BFIR->BFER and left-hand ->
> > > > > > >       right-hand:
> > > > > > >       >
> > > > > > >       > Consider how redundant disjoint traffic can reach BFER1/BFER2 in
> > > > > > >       above
> > > > > > >       > picture: When BFER1/BFER2 are Non-Leaf BFER as shown on the
> > > > > > >       right hand
> > > > > > >       > side, one traffic copy would be forwarded to BFER1 from BFR1,
> > > > > > >       but the
> > > > > > >       > other one could only reach BFER1 via BFER2, which makes BFER2 a
> > > > > > >       > non-Leaf BFER. Likewise BFER1 is a non-Leaf BFER when forwarding
> > > > > > >       > traffic to BFER2
> > > > > > >       >
> > > > > > >       > > Zzh> Additionally, in left part of the picture you added, if
> > > > > > >       some failure leads to BFR2 to be only reachable via BFER1, then
> > > > > > >       BFER1 is no longer a leaf BFER.
> > > > > > >       >
> > > > > > >       > Added sentence:
> > > > > > >       >
> > > > > > >       > <t>Note that the BFER in the left hand picture are only
> > > > > > >       guaranteed to
> > > > > > >       > be leaf-BFR by fitting routing configuration that prohibits transit
> > > > > > >       > traffic to pass through a PE, which is commonly applied in these
> > > > > > >       > topologies.</t>
> > > > > > >       >
> > > > > > >       > > I assume you don't reassign BPs when links go up and down.
> > > > > > >       >
> > > > > > >       > I didn't want to discuss that option in this document. Its
> > > > > > >       obviously
> > > > > > >       > perfectly feasible, but be yet a big amount of text (especially the
> > > > > > >       > considerations how to do this make-before-break. Future doc.
> > > > > > >       >
> > > > > > >       > > > but subsequent polarization example confuses me. It seems
> > > > > > >       that BP 0:6 is assigned to the routed adjacency BFR10 (which is
> > > > > > >       actually talked about in Section 4.8).
> > > > > > >       > >
> > > > > > >       > > Section 4.7 does not mention "routed" at all, so there are no
> > > > > > >       routed adjacencies at all used in 4.7. So i am not sure what you
> > > > > > >       are confused about.
> > > > > > >       > >
> > > > > > >       > > Zzh> "The BIFT of each BFR are only populated with BPs that
> > > > > > >       are adjacent to the BFR in the BIER-TE topology".
> > > > > > >       >
> > > > > > >       > Correct text from the introduction. Ok.
> > > > > > >       >
> > > > > > >       > > Zzh> Since the same 0:6 is in BIFTS of BFR1/BFR2/BFR3 (and I
> > > > > > >       suppose in BFR4~BFR9 as well even though not drawn), I assumed
> > > > > > >       it's for the "MP2P" routed adjacency to R10; though I then ruled
> > > > > > >       that out - but I don't know what 0:6 represent now on BFR1, BFR2,
> > > > > > >       and BFR3.
> > > > > > >       >
> > > > > > >       > Ah. Ok. I thought i could strip down the example to show only the
> > > > > > >       > adjacencies relevant to the following discusion, but seemingly this
> > > > > > >       > can introduce the confusion you have.
> > > > > > >       >
> > > > > > >       > So i completed the example with the BP assignment acoss all
> > > > > > >       nodes, but
> > > > > > >       > added text pointing to a new section further down to discuss the
> > > > > > >       > re-use of BP for which thi picture is also an example.
> > > > > > >       >
> > > > > > >       > (check out the diff, new reuse text to long to copy inline).
> > > > > > >       >
> > > > > > >       > > The whole purpose of the ECMP BPs is of course to save bits,
> > > > > > >       otherwise we'd give each link a separate BP, which would be 6 BP
> > > > > > >       to reach to BFR4...BFR7 from BFR1.
> > > > > > >       > >
> > > > > > >       > > Zzh> The trouble I am having is that the same 0:6 is assigned
> > > > > > >       to different things and it's present on all BFR1/BFR2/BFR3. It is
> > > > > > >       perhaps an intentional smart design but I have not wrapped my mind
> > > > > > >       around it. It's apparently different from the link bundle case, so
> > > > > > >       better separate it out and elaborate it (including the DNR flag
> > > > > > >       that might be needed here - If the packet arrives on BFR1 with
> > > > > > >       0:6, would the BP reset when it is sent to BFR2/3)?
> > > > > > >       >
> > > > > > >       > Yes, there was the bug of reusing BP 0:6 across sequential BFR
> > > > > > >       along
> > > > > > >       > the path, but now the example correctly reuses separate BP at
> > > > > > >       > different stages of the paths (BP 0:6 on BFR1, BP 0:7 on
> > > > > > >       BFR2/BFR3) and so on.
> > > > > > >       >
> > > > > > >       > Thanks!
> > > > > > >       >
> > > > > > >       > > > 4.8.  Routed adjacencies
> > > > > > >       > > >
> > > > > > >       > > > If I understand it correctly, there is a BP assigned to
> > > > > > >       L1/L2/L3
> > > > > > >       > > > respectively (p2p link), and then there are BPs assigned to
> > > > > > >       MP2P tunnels (routed adjacency from every BFR) to the L1/L2/L3
> > > > > > >       interface addresses and loopback addresses on BFR2/3.
> > > > > > >       > >
> > > > > > >       > > Ok that wasn't quite the read i expected. Let me clarify the
> > > > > > >       text/picture:
> > > > > > >       > >
> > > > > > >       > >                    ...............
> > > > > > >       > >          ...BFR1--...           ...--L1-- BFR2...
> > > > > > >       > >                   ... .Routers. ....--L2--/
> > > > > > >       > >          ...BFR4--...           ...------ BFR3...
> > > > > > >       > >                    ................         |
> > > > > > >       > >                                           LO
> > > > > > >       > >                     Network Area 1
> > > > > > >       > >
> > > > > > >       > > Assume the requirement in the above picture is to explicitly
> > > > > > >       steer traffic flows that have arrived at BFR1 or BFR4 via a
> > > > > > >       shortest path in the routing underlay "network area 1" to one of
> > > > > > >       the following three next segments: (1) BFR2 via link L1, (2) BFR2
> > > > > > >       via link L2, (3) via BFR3.
> > > > > > >       > >
> > > > > > >       > > To achieve this, both BFR1 and BFR4 are set up with a
> > > > > > >       forward_routed adjacency BitPosition towards an address of BFR2 on
> > > > > > >       link L1, another forward_routed BitPosition towards an address of
> > > > > > >       BFR2 on link L2 and a third forward_routed Bitposition towards a
> > > > > > >       node address LO of BFR3.
> > > > > > >       > >
> > > > > > >       > > Does this clear ip the confusion ?
> > > > > > >       > >
> > > > > > >       > > Zzh> The picture is badly misaligned. I'll wait till 4.7
> > > > > > >       questions are cleared.
> > > > > > >       >
> > > > > > >       > Ok.
> > > > > > >       >
> > > > > > >       > > > If BFR2/3 are also BFERs, then they additionally will have
> > > > > > >       BFER BPs.
> > > > > > >       > > > On BFR1/4, the BIFT entries for the MP2P BPs for the
> > > > > > >       L1/L2/L3/loopback interface addresses of BFR2/3 will use
> > > > > > >       forward_routed(interface/loopback address). For a packet to be
> > > > > > >       decapsulated on a BFER, there is a need for both the BFER BP and
> > > > > > >       another BP (p2p/lan/hub-spoke/routed-adjacency) in the packet (the
> > > > > > >       former is for decapsulation and the latter is for getting it there).
> > > > > > >       > >
> > > > > > >       > > This is not discussed in this section, but you are right - unless
> > > > > > >       > > BFR2 or BFR3 is a leaf BFR. In that case, it would just
> > > > > > >       leverage the one shared "leaf-BFR" BP, so they do not need a
> > > > > > >       per-BFER BP for local_decap().
> > > > > > >       > >
> > > > > > >       > > Zzh> Right - shared leaf-BFR BP but still need that BP (the
> > > > > > >       key is that we need a BP to get packet to a BFER and then a BP for
> > > > > > >       decapsulation).
> > > > > > >       >
> > > > > > >       > You got it.
> > > > > > >       >
> > > > > > >       > > > If that???s the case, it???s worth point the above out.
> > > > > > >       > >
> > > > > > >       > > Hmm... The logic of BFER BPs is totally independent of the
> > > > > > >       logic of forward_routed adjacency, so i would worry that repeating
> > > > > > >       the explanation of BFER BPs would conflate the forward_routed
> > > > > > >       explanation.
> > > > > > >       > >
> > > > > > >       > > Zzh> It's just that this is a place where all kinds of BPs are
> > > > > > >       used so it's good to have a summary (could be a subsection 4.9).
> > > > > > >       >
> > > > > > >       > Yes, added such a summary. Pls. check.
> > > > > > >       >
> > > > > > >       > > > Actually, the reason that I thought this is MP2P is that 0:6
> > > > > > >       is present on R1, R2, and R3 (and more I assume) in Figure 12, but
> > > > > > >       now I think it can???t be MP2P (so it is not correct to have 0:6
> > > > > > >       present on those routers ??? only the p2p tunnel head/tail should
> > > > > > >       have the BP present in the BIFT). The reason is that if it were
> > > > > > >       MP2P, any router getting a copy will send it to the endpoint of
> > > > > > >       the routed adjacency, causing lots of duplicates.
> > > > > > >       > > >
> > > > > > >       > > > Am I getting this correct?
> > > > > > >       > >
> > > > > > >       > > I think you are still explaining from the misunderstsanding
> > > > > > >       that the ECMP explanations where about routed adjacencies.
> > > > > > >       > >
> > > > > > >       > > I have now expanded the somewhat terse text in the BIFT table
> > > > > > >       pictures, to make it clear that the ECMP is across multipe
> > > > > > >       forward_connected adjacencies in the examples. For example, first
> > > > > > >       BIFT picture:
> > > > > > >       > >
> > > > > > >       > >   BIFT entry in BFR1:
> > > > > > >       > >
> > > > > > >        ------------------------------------------------------------------
> > > > > > >       > >   | Index |  Adjacencies                  |
> > > > > > >       > >
> > > > > > >        ==================================================================
> > > > > > >       > >   | 0:6   |  ECMP({forward_connected(L1, BFR2),                 |
> > > > > > >       > >   |       |        forward_connected(L2, BFR2),                 |
> > > > > > >       > >   |       |        forward_connected(L3, BFR2)}, seed)
> > > > > > >            |
> > > > > > >       > >
> > > > > > >        ------------------------------------------------------------------
> > > > > > >       > >
> > > > > > >       > > Of course, an ECMP adjacency can be across any type of
> > > > > > >       adjacencies, but all the text/explanations used forward_connected,
> > > > > > >       and now the pictures show that explicitly.
> > > > > > >       > >
> > > > > > >       > > Zzh> I can understand the multi-link case, but the multi-hop
> > > > > > >       ECMP case (from BFR1 towards BFR10) is confusing me. It would help
> > > > > > >       to give an example how it can be used, WITHOUT worrying about
> > > > > > >       polarization.
> > > > > > >       >
> > > > > > >       > Please check -05 text that has the full set of BIFT listed now:
> > > > > > >       >
> > > > > > >       > There is  really nothing nothing unique in multi-hop ECMP for
> > > > > > >       BIER-TE
> > > > > > >       > that we do not also have in any other ECMP, except the
> > > > > > >       conclusion that
> > > > > > >       > we want to support fast HW hash mechanisms AND allow the
> > > > > > >       controller to
> > > > > > >       > set up non-polarized multi-hop ECMP AND be able to precalculate
> > > > > > >       paths.
> > > > > > >       > Hence the specification of ECMP adjacencies to have a controller
> > > > > > >       > configurable seed.
> > > > > > >       >
> > > > > > >       > Btw: The picture is maybe unnecessarily large because i've used
> > > > > > >       it for
> > > > > > >       > 20 years to explain the same polarization issue for unicast vs
> > > > > > >       > multicast, and for multicast only BFR10...BFR4 are relevant
> > > > > > >       (ECMP of
> > > > > > >       > the PIM/mLDP joins), whereas for unicast/BIER only
> > > > > > >       > BFR1...BFR7 are relevant. But being symmetric, the picture makes it
> > > > > > >       > clear its the same problem.
> > > > > > >       >
> > > > > > >       > > >    To inhibit looping in the face of such physical
> > > > > > >       misconfiguration,
> > > > > > >       > > >    only forward_connected adjacencies are permitted to have
> > > > > > >       DNR set, and
> > > > > > >       > > >    the link layer destination address of the adjacency
> > > > > > >       (e.g.  MAC
> > > > > > >       > > >    address) protects against closing the loop.  Link layers
> > > > > > >       without port
> > > > > > >       > > >    unique link layer addresses should not be used with the
> > > > > > >       DNR flag set.
> > > > > > >       > > >
> > > > > > >       > > > It???s not clear how link layer address helps?
> > > > > > >       > >
> > > > > > >       > > I have expanded this to
> > > > > > >       > > "link layer port unique unicast destination address"
> > > > > > >       > >
> > > > > > >       > > Aka: MPLS or ethernet have unique link layer destination
> > > > > > >       destination addresses (label or destination MAC). If you think
> > > > > > >       about incorrectly plugged HDLC links (such as old T1/T3/....
> > > > > > >       links), they only have 2 generic addresses, if i remember 1 or 3
> > > > > > >       in the HDLC frame. So when you misplug one of those p2p cables
> > > > > > >       wrong, the packets would be incrrectly received by the wrong
> > > > > > >       receiver node and then DNR could cause persistent loops only
> > > > > > >       solved by TTL.
> > > > > > >       > >
> > > > > > >       > > Zzh> "Consider in the ring picture that link L4 from BFR3 is
> > > > > > >       plugged into the L1 interface of BFRa" - still not sure how
> > > > > > >       label/mac helps here. I suppose the ring topology is
> > > > > > >       discovered/verified by the control plane and when the miscalling
> > > > > > >       happens then the ring will not include the BFR1/BFR2 part and BFR3
> > > > > > >       will not have the DNR set? If ring discovery/varication is not
> > > > > > >       done then perhaps we should point out that RPF based on link layer
> > > > > > >       address is needed - the key is RPF (which needs unique link layer
> > > > > > >       address)?
> > > > > > >       >
> > > > > > >       > Forget RPF. BIER(-TE) has no RPF (issues). Its just like
> > > > > > >       unicast. RPF
> > > > > > >       > is just a problem for receiver originated joins like in
> > > > > > >       PIM/mLDP, but
> > > > > > >       > not unicast/bier(-te)/RSVP-TE.
> > > > > > >       >
> > > > > > >       > Forward_connected is just like a unicast subnet adjacency to a
> > > > > > >       direct
> > > > > > >       > neighbor: Interface and L2 addresss of the destination.
> > > > > > >       >
> > > > > > >       > The controller (could be a human) "assumes" a particular physicial
> > > > > > >       > topology, from telemetry/knowledge/whatever. It then calculates the
> > > > > > >       > desired BIER-TE topology and pushes it down. This topology is
> > > > > > >       meant to
> > > > > > >       > be loop free of course wrt to the configured adjacencies.
> > > > > > >       > In this BIER-TE topology, BFR3 will have a BP with the
> > > > > > >       > forward_connected(L4, MAC-of-BFR2) adjacency.
> > > > > > >       >
> > > > > > >       > If the cable connecting to L4 is miswired, then BFR3 would still
> > > > > > >       send
> > > > > > >       > the packets to the MAC address of BFR2, but given how the cable
> > > > > > >       > connects to some other node, these packets will be discarded by
> > > > > > >       that
> > > > > > >       > node. because they're just L2 unicast packets.
> > > > > > >       >
> > > > > > >       > I think this is equally true when we have normal BIER/MPLS enacp.
> > > > > > >       > Those packets too are addressed to the unicast MAC address of the
> > > > > > >       > neighbor.
> > > > > > >       >
> > > > > > >       > Now, if/when he controller recognizes that the physical topology
> > > > > > >       has
> > > > > > >       > changed, thats a completely different story and not addressed here.
> > > > > > >       > Given how we assumed this was a cabling mistake, the controller
> > > > > > >       would
> > > > > > >       > probably only complain about the miswiring to operations but be
> > > > > > >       happy
> > > > > > >       > that the forwarding plane just makes packets fail instead of
> > > > > > >       loop. If
> > > > > > >       > this was a planned change process, then it will be similarily
> > > > > > >       > convoluted as it would today be with rewiring cables in an
> > > > > > >       > SR-MPLS/SRv6 topology and updating SIDs.
> > > > > > >       >
> > > > > > >       > > > Because the forwarding is different from BIER forwarding
> > > > > > >       (because of [1] above), we might as well introduce an optimization
> > > > > > >       here ??? for each BIFT, calculate the F-BM of the BIFT itself (the
> > > > > > >       logical ???or??? of all the BPs presented in this BIFT) and then
> > > > > > >       use (packet->bitstring & BIFT.F-BM) as the input to
> > > > > > >       GetFirst/NextBitPosition(). That should skip many bits.
> > > > > > >       > >
> > > > > > >       > > Right. But i explicitly removed those optimizations (i had
> > > > > > >       them in older draft versions) because the whole idea of this
> > > > > > >       picture is solely the comparison with figure 4 of RFC8279.
> > > > > > >       > >
> > > > > > >       > > Zzh> I think it's worth point that optimization out; you can
> > > > > > >       mark it optional if you want to emphasize the similarity to BIER
> > > > > > >       forwarding, but since BIER forwarding does do the maskoff step, it
> > > > > > >       is very efficient while BIER-TE forwarding does not it the maskoff
> > > > > > >       step so this optimization is important.
> > > > > > >       >
> > > > > > >       > Ok. I simplified the text comparison BIER/BIER-TE wrt. to the FBM
> > > > > > >       > rules [1] and [2] and added following paragraph:
> > > > > > >       >
> > > > > > >       > <t>In BIER, the order of BPs impacts the result of forwarding
> > > > > > >       because of [1].
> > > > > > >       > In BIER-TE, forwarding is not impacted by the order of BPs. It is
> > > > > > >       > therefore possible to further optimize forwarding than in BIER. For
> > > > > > >       > example parallelizing forwarding across multiple FPE cores or
> > > > > > >       > distributed linecards does only need to examine an arbitrary
> > > > > > >       subset of
> > > > > > >       > BP and not evaluate the dependency between BPs.</t>
> > > > > > >       >
> > > > > > >       > > >    The following pseudocode is comprehensive:
> > > > > > >       > > >
> > > > > > >       > > > The above sentence reads a bit strange (or lacks some segue).
> > > > > > >       > >
> > > > > > >       > > I hope not, but maybe best left to a native english speaker
> > > > > > >       (RFC-editor).
> > > > > > >       > >
> > > > > > >       > > The first (RFC8279) pseudocode was simplified. The second one
> > > > > > >       is comprehensive. If not comprehensive, whats a good opposite of
> > > > > > >       simplified ?
> > > > > > >       > >
> > > > > > >       > > Zzh> Perhaps "The above simplified pseudocode is elaborated
> > > > > > >       further as following"?
> > > > > > >       > > Zzh> Jeffrey
> > > > > > >       >
> > > > > > >       > Done.
> > > > > > >       >
> > > > > > >       > Thanks a lot.
> > > > > > >       >
> > > > > > >       >
> > > > > > >       > >
> > > > > > >       > > > ________________________________________
> > > > > > >       > > > From: BIER [[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail]
> > > > > > >       <mailto:[e-mail]>>]
> > > > > > >       > > > on behalf of Toerless Eckert [[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail] <mailto:[e-mail]..de>>]
> > > > > > >       > > > Sent: Tuesday, July 09, 2019 23:38
> > > > > > >       > > > To: Mike McBride
> > > > > > >       > > > Cc: Greg Shepherd; BIER WG; Pascal Thubert (pthubert)
> > > > > > >       > > > Subject: Re: [Bier] WGLC - draft-ietf-bier-te-arch
> > > > > > >       > > >
> > > > > > >       > > > Thanks, Mike
> > > > > > >       > > >
> > > > > > >       > > > The authors also reviewed the document and concluded that it
> > > > > > >       was
> > > > > > >       > > > really hard to get into the document context because of too
> > > > > > >       many
> > > > > > >       > > > forward dependencies. We tried to fix this by adding two
> > > > > > >       hopefully
> > > > > > >       > > > good & basic examples into the Introduction section and
> > > > > > >       using them
> > > > > > >       > > > to also add a better definition of the term "BIER-TE
> > > > > > >       Topology" in the Introduction.
> > > > > > >       > > > Hopefully this makes readin the rest of te document smoother.
> > > > > > >       > > >
> > > > > > >       > > > Also improved text of Abstract and refined text compariing
> > > > > > >       BIER-TE with SR.
> > > > > > >       > > >
> > > > > > >       > > >
> > > > > > >       https://urldefense.com/v3/__http://tools.ietf.org/*rfcdiff?url1=https:
> > > > > > >       > > > **Atools.ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__Atools.ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=ggPrkSBziBxcUV48NKmskrw6fOzU94m3Dk5u67UMcRg&e= >*id*draft-ietf-bier-te-arch-02.txt&url2=https:**A
> > > > > > >       > > > tool
> > > > > > >       > > > s.ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__s.ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=Ox8APr0AU8iMaNjaWNcGYQDfkrhJBNtsAZWRvfmO_ZI&e= >*id*draft-ietf-bier-te-arch-03.txt__;Ly8vLy8vLy8v!8WoA6R
> > > > > > >       > > > jC81
> > > > > > >       > > >
> > > > > > >       c!XvH4AAxfrDjFoK_sercwZMsc0O5N42eENOs4l_qdsXF0KwZD82cJLDFFNV_eTUEh
> > > > > > >       > > > $
> > > > > > >       > > >
> > > > > > >       <https://urldefense.com/v3/__http:/tools.ietf.org/*rfcdiff?url1=https:
> > > > > > >       > > > **Atools.ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__Atools.ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=ggPrkSBziBxcUV48NKmskrw6fOzU94m3Dk5u67UMcRg&e= >*id*draft-ietf-bier-te-arch-02.txt&url2=https:**A
> > > > > > >       > > > tool
> > > > > > >       > > > s.ietf.org
> > > > > > >       <https://urldefense.proofpoint.com/v2/url?u=http-3A__s.ietf.org&d=DwIFAw&c=LFYZ-o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=MW3S0mvhNN9uq5VmjXdNXGwsisVP5wzzO8r04h4aP0o&s=Ox8APr0AU8iMaNjaWNcGYQDfkrhJBNtsAZWRvfmO_ZI&e= >*id*draft-ietf-bier-te-arch-03.txt__;Ly8vLy8vLy8v!8WoA6R
> > > > > > >       > > > jC81
> > > > > > >       > > >
> > > > > > >       c!UBTGvWWpMHyeiSanxs6vIb_EnBVgyg6boAAW4nrqju8UCLOgiuXc8Y_6sNd1njcX
> > > > > > >       > > > $>
> > > > > > >       > > >
> > > > > > >       > > > Cheers
> > > > > > >       > > >     Toerless
> > > > > > >       > > >
> > > > > > >       > > > On Wed, Jun 26, 2019 at 10:39:36AM -0700, Mike McBride wrote:
> > > > > > >       > > > > How about three? I support.
> > > > > > >       > > > > mike
> > > > > > >       > > > >
> > > > > > >       > > > > On Tue, Jun 25, 2019 at 10:42 AM Greg Shepherd
> > > > > > >       <[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail]
> > > > > > >       <mailto:[e-mail]>>> wrote:
> > > > > > >       > > > > >
> > > > > > >       > > > > > We cannot take two 'yes' votes and WG consensus.
> > > > > > >       > > > > > Please, read and respond. If you don't support, then
> > > > > > >       please vote as much publicly right here.
> > > > > > >       > > > > >
> > > > > > >       > > > > > Thanks,
> > > > > > >       > > > > > Greg
> > > > > > >       > > > > >
> > > > > > >       > > > > > On Mon, Jun 3, 2019 at 10:05 PM Pascal Thubert
> > > > > > >       (pthubert) <[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail]
> > > > > > >       <mailto:[e-mail]>>> wrote:
> > > > > > >       > > > > >>
> > > > > > >       > > > > >> Support:
> > > > > > >       > > > > >>
> > > > > > >       > > > > >> I see great value in deterministic networks as well as
> > > > > > >       IOT (with RPL).
> > > > > > >       > > > > >>
> > > > > > >       > > > > >> All the best,
> > > > > > >       > > > > >>
> > > > > > >       > > > > >> Pascal
> > > > > > >       > > > > >>
> > > > > > >       > > > > >> > -----Original Message-----
> > > > > > >       > > > > >> > From: BIER
> > > > > > >       > > > > >> > <[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail]
> > > > > > >       <mailto:[e-mail]>>> On
> > > > > > >       > > > > >> > Behalf Of Toerless Eckert
> > > > > > >       > > > > >> > Sent: mardi 4 juin 2019 02:03
> > > > > > >       > > > > >> > To: Greg Shepherd
> > > > > > >       > > > > >> > <[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail]
> > > > > > >       <mailto:[e-mail]>>>
> > > > > > >       > > > > >> > Cc: BIER WG <[e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail] <mailto:[e-mail]>>>
> > > > > > >       > > > > >> > Subject: Re: [Bier] WGLC - draft-ietf-bier-te-arch
> > > > > > >       > > > > >> >
> > > > > > >       > > > > >> > +1
> > > > > > >       > > > > >> > Obviously support as co-author.
> > > > > > >       > > > > >> >
> > > > > > >       > > > > >> > On Wed, May 29, 2019 at 12:41:26PM -0700, Greg
> > > > > > >       Shepherd wrote:
> > > > > > >       > > > > >> > > Please read and respond to this thread w/ or w/o
> > > > > > >       support.
> > > > > > >       > > > > >> > >
> > > > > > >       > > > > >> > >
> > > > > > >       https://urldefense.com/v3/__https://datatracker..ietf.org
> > > > > > >       > > > > >> > > /doc
> > > > > > >       > > > > >> > >
> > > > > > >       /draft-ietf-bier-te-arch/__;!8WoA6RjC81c!XvH4AAxfrDjFoK_s
> > > > > > >       > > > > >> > > ercw ZMsc0O5N42eENOs4l_qdsXF0KwZD82cJLDFFNV9eClBj$
> > > > > > >       > > > > >> > >
> > > > > > >       <https://urldefense.com/v3/__https:/datatracker.ietf.org/
> > > > > > >       > > > > >> > > doc/
> > > > > > >       > > > > >> > >
> > > > > > >       draft-ietf-bier-te-arch/__;!8WoA6RjC81c!UBTGvWWpMHyeiSanx
> > > > > > >       > > > > >> > > s6vI b_EnBVgyg6boAAW4nrqju8UCLOgiuXc8Y_6sD40kmtH$>
> > > > > > >       > > > > >> > >
> > > > > > >       > > > > >> > > Vote ends 5 June 2019.
> > > > > > >       > > > > >> > >
> > > > > > >       > > > > >> > > Thanks,
> > > > > > >       > > > > >> > > Shep
> > > > > > >       > > > > >> > > (chairs)
> > > > > > >       > > > > >> >
> > > > > > >       > > > > >> > > _______________________________________________
> > > > > > >       > > > > >> > > BIER mailing list
> > > > > > >       > > > > >> > > [e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail] <mailto:[e-mail]>>
> > > > > > >       > > > > >> > >
> > > > > > >       https://urldefense.com/v3/__https://www.ietf.org/mailman/
> > > > > > >       > > > > >> > > list
> > > > > > >       > > > > >> > >
> > > > > > >       info/bier__;!8WoA6RjC81c!XvH4AAxfrDjFoK_sercwZMsc0O5N42eE
> > > > > > >       > > > > >> > > NOs4 l_qdsXF0KwZD82cJLDFFNT2WVXWX$
> > > > > > >       > > > > >> > >
> > > > > > >       <https://urldefense.com/v3/__https:/www.ietf.org/mailman/
> > > > > > >       > > > > >> > > list
> > > > > > >       > > > > >> > >
> > > > > > >       info/bier__;!8WoA6RjC81c!UBTGvWWpMHyeiSanxs6vIb_EnBVgyg6b
> > > > > > >       > > > > >> > > oAAW 4nrqju8UCLOgiuXc8Y_6sKn2KoAT$>
> > > > > > >       > > > > >> >
> > > > > > >       > > > > >> > _______________________________________________
> > > > > > >       > > > > >> > BIER mailing list
> > > > > > >       > > > > >> > [e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail] <mailto:[e-mail]>>
> > > > > > >       > > > > >> >
> > > > > > >       https://urldefense.com/v3/__https://www.ietf.org/mailman/li
> > > > > > >       > > > > >> > stin
> > > > > > >       > > > > >> >
> > > > > > >       fo/bier__;!8WoA6RjC81c!XvH4AAxfrDjFoK_sercwZMsc0O5N42eENOs4
> > > > > > >       > > > > >> > l_qd
> > > > > > >       > > > > >> > sXF0KwZD82cJLDFFNT2WVXWX$
> > > > > > >       > > > > >> >
> > > > > > >       <https://urldefense.com/v3/__https:/www.ietf.org/mailman/li
> > > > > > >       > > > > >> > stin
> > > > > > >       > > > > >> >
> > > > > > >       fo/bier__;!8WoA6RjC81c!UBTGvWWpMHyeiSanxs6vIb_EnBVgyg6boAAW
> > > > > > >       > > > > >> > 4nrq
> > > > > > >       > > > > >> > ju8UCLOgiuXc8Y_6sKn2KoAT$>
> > > > > > >       > > > > >
> > > > > > >       > > > > > _______________________________________________
> > > > > > >       > > > > > BIER mailing list
> > > > > > >       > > > > > [e-mail]
> > > > > > >       <mailto:[e-mail]><mailto:[e-mail] <mailto:[e-mail]>>
> > > > > > >       > > > > >
> > > > > > >       https://urldefense.com/v3/__https://www.ietf.org/mailman/listi
> > > > > > >       > > > > > nfo/
> > > > > > >       > > > > >
> > > > > > >       bier__;!8WoA6RjC81c!XvH4AAxfrDjFoK_sercwZMsc0O5N42eENOs4l_qdsX
> > > > > > >       > > > > > F0Kw
> > > > > > >       > > > > > ZD82cJLDFFNT2WVXWX$
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> > > > > > >       <https://urldefense.com/v3/__https:/www.ietf.org/mailman/listi
> > > > > > >       > > > > > nfo/
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> > > > > > >       bier__;!8WoA6RjC81c!UBTGvWWpMHyeiSanxs6vIb_EnBVgyg6boAAW4nrqju
> > > > > > >       > > > > > 8UCL
> > > > > > >       > > > > > OgiuXc8Y_6sKn2KoAT$>
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> > > > > > >       https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/
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> > > > > > >       > > > cJLD
> > > > > > >       > > > FFNT2WVXWX$
> > > > > > >       > > >
> > > > > > >       <https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/
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> > > > > > >       > > > Xc8Y
> > > > > > >       > > > _6sKn2KoAT$>
> > > > > > >       > >
> > > > > > >       > > --
> > > > > > >       > > ---
> > > > > > >       > > [e-mail] <mailto:[e-mail]>
> > > > > > >       >
> > > > > > >       > --
> > > > > > >       > ---
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> > > > > > >       https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/bier
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> > > > > > >       > 1_jWV3YUA6D$
> > > > > > > 
> > > > > > >       --
> > > > > > >       ---
> > > > > > >       [e-mail] <mailto:[e-mail]>
> > > > > > > 
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> > > > > > > 
> > > > > > _______________________________________________
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