RE: Deborah Brungard's Discuss on draft-ietf-rtgwg-backoff-algo-07: (with DISCUSS)

<bruno.decraene@orange.com> Wed, 28 February 2018 15:45 UTC

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From: <bruno.decraene@orange.com>
To: "BRUNGARD, DEBORAH A" <db3546@att.com>
CC: "rtgwg@ietf.org" <rtgwg@ietf.org>, "rtgwg-chairs@ietf.org" <rtgwg-chairs@ietf.org>, Uma Chunduri <uma.chunduri@huawei.com>, "draft-ietf-rtgwg-backoff-algo@ietf.org" <draft-ietf-rtgwg-backoff-algo@ietf.org>, "Acee Lindem (acee)" <acee@cisco.com>, The IESG <iesg@ietf.org>, Alvaro Retana <aretana.ietf@gmail.com>
Subject: RE: Deborah Brungard's Discuss on draft-ietf-rtgwg-backoff-algo-07: (with DISCUSS)
Thread-Topic: Deborah Brungard's Discuss on draft-ietf-rtgwg-backoff-algo-07: (with DISCUSS)
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Date: Wed, 28 Feb 2018 15:44:54 +0000
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Hi Deborah,

Please see inline

 > -----Original Message-----
 > From: BRUNGARD, DEBORAH A [mailto:db3546@att.com]
 > Sent: Wednesday, February 28, 2018 12:48 PM
>
 > 
 > Hi Acee,
 > 
 > I think Alvaro is on vacation this week without email access. As I noted in my Discuss, I support
 > Alvaro's concerns on incompleteness and vagueness. I am interested in Alvaro's response on the
 > update if it addresses his concerns.

1) Regarding Alvaro's DISCUSS,
We have engaged the discussion on his points. Thanks for the info that he is on vacation this week. No problem, we'll obviously wait for this return.

2) Regarding your DISCUSS,
Can we work on resolving your point and hopefully your DISCUSS even in the absence of Alvaro?

As a reminder, your DISCUSS is the following:

"While I agree with Alvaro's concerns, my concern is the appropriateness of this document as PS.
This document should have a similar status as RFC6976 (Informational) which also provided a
mechanism that prevented transient loops saying "the mechanisms described in this
document are purely illustrative of the general approach and do not constitute a protocol

specification". Especially as this document compares itself to RFC6976, saying RFC6976 is a
"full solution".

With a change of status to Informational, this document would be better scoped as providing guidance vs. a specification."




So in summary your DISCUSS is about the status of this document: STD track vs informational.

Acee has replied on this point in the following thread, and ultimately you did not follow up. So I though the point was closed.
https://mailarchive.ietf.org/arch/msg/rtgwg/pqGrmtI7MYVqU8tSNwId-QEROYs
So could you please follow up on this thread so that we can advance on this point?
I'll also contribute below in this email in reply to your specific comments.

Regarding STD status, a distributed Link State IGP, requires, in order to produce consistent routing table across the network, to perfom the same computation (SPF), using the same info/database, at the same time.
Given that all implementations use SPF back off delay algorithms (by default), in order to fulfill this routing consistency across the network, one STD SPF back off delay algo needs to be specific. By doing so, this document helps addressing the above two latest points (same time, same LSDB).

Also, in case you missed it as the email was in a different thread, Alia has also stated that this needs to be standard track.
https://mailarchive.ietf.org/arch/msg/rtgwg/EDpT9lvKVDaBjI8g_QHznZMdTNI



3) Regarding your new additional comments below

It's not clear to me whether they are additional points in your DISCUSS or just regular comments.
Reading the discuss criteria, they really likes non-blocking comments to me.
https://www.ietf.org/iesg/statement/discuss-criteria.html

So you could please clarify the status of those comments?

More below.

 > 
 > I don't see any changes for my noted concerns on vagueness.

Acee replied to your email and you did not reply.
As previously noted, I'll also reply on your points in this email, below.


 > The confusing sentence remains in
 > the introduction "Optionally, implementations may also offer alternative algorithms." 

- I'm personally not sure to see what is confusing in this sentence.
- As Acee replied, this is just a statement about the reality of existing implementations and deployments.
- That being said, that sentence does not really add anything to the specification. Hence if this is a blocking point to you, I've just removed it. Problem solved.

  >And later in
 > section 5 saying it "describes the abstract finite state machine".

I'm not sure to see the issue but changed to

OLD: This section describes the abstract finite state machine (FSM)
NEW: This section specifies the finite state machine (FSM)

Also changed (*3):
OLD: FSM abstract timer
NEW: FSM timer


 > So to me, it still is not clear if this document is a PS for the algorithm or for the parameters

The document is a PS for the algorithm.
We have initiated a discussion with Alvaro regarding the additional specification of default parameters for the specific cases where they are useful.

 > e.g. any
 > SPF delay algorithm that supports the IETF parameters can be used so long as it derives the same
 > results of the "abstract" state machine.

I'm not sure how this question is specific to this document.
Personally, I'd tend to generally reply "yes". i.e., considering the node as a black box, if it's behavior conforms to the behavior defined in the IETF document, I'd say that the node is compliant with the IETF document.
e.g., if the IETF document defines a timer of 3 seconds, it looks ok for me if an implementation waits for 3 consecutive 1 second timers. 
But any general answer from the IETF works for me. It seemed to me that the IETF does not give position regarding conformance.

 > Especially considering the deployment concerns for a new algorithm.

I think that you are missing that the current situation is worse: if you have a multi-vendor networks, you already have inconsistent algorithms forever hence you (may) have inconsistent timers values forever.
If/When you transition to this new algorithm, you also have inconsistent algorithms during the transition (*), but after the transition, the problem is solved. 
(*) whether the situation is worse during the transition or not, is very dependent on the pre-existing algo.

Also, this inconsistency is essentially the same than the transition of parameters values. And this already happen today, including in a mono-vendor network. e.g.,   https://www.cisco.com/c/en/us/support/docs/ip/ip-routing/211432-Change-of-Default-OSPF-and-IS-IS-SPF-and.html
Please note that deployment section from the above document says essentially the same:

"When you deploy routers with newer Cisco IOS software that have the new default values, it is recommended to ensure that all routers have the same default values for the timers. This reduces the risk for possible routing loops. 

If you have routers that run the old default values and you upgrade the routers to the newer Cisco IOS software, it is likely that you have a migration time where some routers run an older Cisco IOS software with the old default values and some routers that run newer IOS software with the new default values. This is not recommended."


Bottom line: blocking this document does not avoid a possible transition issue, but avoids solving the existing forever issue in multi-vendor network.


 > As other ADs agree with me, this type of document is typically informational. Maybe with
 > Alvaro's clarifications, it will not be so abstract.
 
We are indeed working on Alvaro's comment.

 > The naming of the algorithm is also vague.
 
I guess that the discussion on the name is not a DISCUSS/blocking-issue. Is this?

 
 > There are only two uses of "backoff", in the title and in the abstract. The document uses "SPF
 > delay algorithm".

The document defines a "backoff" procedure for the IGP SPF, by introducing a delay and a delay which is increasing as the IGP keeps computing SPFs.
This document defines the algorithm/procedure computing this delay.

 > Looking at the ospf-yang document, it doesn't reference this document or use the feature name
 > "backoff algorithm". It refers to an "SPF delay algorithm" and lists the parameters. Either "backoff"
 > or "SPF delay" naming should be used consistently if it is the titled algorithm which is PS.

Good comments. But those are for the YANG documents. Not this one.

Thanks
--Bruno

 > 
 > Thanks,
 > Deborah
 > 
 > 
 > -----Original Message-----
 > From: iesg [mailto:iesg-bounces@ietf.org] On Behalf Of Acee Lindem (acee)
 > Sent: Tuesday, February 27, 2018 2:36 PM
 > To: BRUNGARD, DEBORAH A <db3546@att.com>om>; The IESG <iesg@ietf.org>rg>; Alvaro Retana
 > <aretana.ietf@gmail.com>
 > Cc: rtgwg@ietf.org; rtgwg-chairs@ietf.org; Uma Chunduri <uma.chunduri@huawei.com>om>; draft-
 > ietf-rtgwg-backoff-algo@ietf.org
 > Subject: Re: Deborah Brungard's Discuss on draft-ietf-rtgwg-backoff-algo-07: (with DISCUSS)
 > 
 > Hi Deborah, Alvaro,
 > 
 > 
 > 
 > Bruno has posted -08 version addressing Alvaro's default timer value request. Can you clear your
 > DISCUSSES?
 > 
 > 
 > 
 > https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-
 > 2Drtgwg-2Dbackoff-2Dalgo_&d=DwIGaQ&c=LFYZ-
 > o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=EanJBdMh8ViXUpOAcuGDU3_m4R
 > EU12AjmiAeQh4TZ5o&s=nNjJEE9Ft49chxnM3q347Q6JACjZaUR3XaoDmZkyXJA&e=
 > 
 > 
 > 
 > Thanks,
 > 
 > Acee
 > 
 > 
 > 
 > On 2/24/18, 8:52 PM, "Acee Lindem (acee)" <acee@cisco.com> wrote:
 > 
 > 
 > 
 >     Hi Deborah,
 > 
 > 
 > 
 >     On 2/24/18, 4:07 PM, "BRUNGARD, DEBORAH A" <db3546@att.com> wrote:
 > 
 > 
 > 
 >         Hi Acee,
 > 
 > 
 > 
 >         Sorry for not responding earlier, I had an unexpected disruption to my schedule these last
 > days.
 > 
 > 
 > 
 >         I was concerned as the document itself says "Optionally, implementations may also offer
 > alternative algorithms." So it is not clear if it is the algorithm or the parameters which are intended
 > PS.
 > 
 > 
 > 
 >     This is the reality that IGP implementations that have been using their proprietary SPF backoff
 > algorithms for decades are not going to move to the standard mechanisms as their default
 > overnight.
 > 
 > 
 > 
 >         And especially concerning is section 7 on partial deployment. It states the algorithm is only
 > effective if it is deployed on all routers, and partial deployment will increase the frequency and
 > duration of micro-loops. It does go on to say operators have progressively replaced an
 > implementation of a given algorithm by a different one.
 > 
 > 
 > 
 >         If this is to be PS, then you need to provide guidance on how an operator is to do the upgrade
 > to this new algorithm on a network. I understand there are prototype implementations, but I'm
 > concerned on field grade deployments in existing networks.
 > 
 > 
 > 
 >     The IETF can't just mandate that vendors implement the new standard SPF backoff algorithm,
 > make it the default SPF Backoff, or that operators deploy it. I believe we have provided ample
 > guidance by indicating that the full benefit is only obtained when the same algorithm is deployed
 > over the IGP domain (or at least an area). The standardization of the SPF Backoff algorithm is the
 > start of the journey, not the destination.
 > 
 > 
 > 
 > 
 > 
 >         Thanks,
 > 
 >         Deborah
 > 
 > 
 > 
 >         -----Original Message-----
 > 
 >         From: Acee Lindem (acee) [mailto:acee@cisco.com]
 > 
 >         Sent: Wednesday, February 21, 2018 7:53 PM
 > 
 >         To: BRUNGARD, DEBORAH A <db3546@att.com>om>; The IESG <iesg@ietf.org>
 > 
 >         Cc: draft-ietf-rtgwg-backoff-algo@ietf.org; Uma Chunduri <uma.chunduri@huawei.com>om>;
 > rtgwg-chairs@ietf.org; rtgwg@ietf.org
 > 
 >         Subject: Re: Deborah Brungard's Discuss on draft-ietf-rtgwg-backoff-algo-07: (with
 > DISCUSS)
 > 
 > 
 > 
 >         Hi Deborah,
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >         Given that the goal of RFC 6976 was much more ambitious and the mechanisms are much
 > more complex, I don't think this draft should be put in the same category.
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >         What we have done is precisely specify a standard algorithm for IGP SPF back-off. When
 > deployed, this standard algorithm will greatly improve (but not eliminate) micro-loops in IGP routing
 > domains currently utilizing disparate SPF back-off algorithms. The problem statement draft best
 > articulates the impact of differing SPF back-off algorithms:
 > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ietf.org_id_draft-2Dietf-2Drtgwg-2Dspf-
 > 2Duloop-2Dpb-2Dstatement-2D06.txt&d=DwIGaQ&c=LFYZ-
 > o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=lB8O9Nd8E9rpRoJj0YX-
 > mV3Tpp8iWGOSIp_fkDPkMuA&s=Vtva23qDNV_XHrGXH4C87wmfZuLcxGEDJAXqVihSSPw&
 > e= . Finally, there have been several prototype implementations validating the algorithm
 > specification's completeness and clarity.
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >         Thanks,
 > 
 > 
 > 
 >         Acee
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             Deborah Brungard has entered the following ballot position for
 > 
 > 
 > 
 >             draft-ietf-rtgwg-backoff-algo-07: Discuss
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             When responding, please keep the subject line intact and reply to all
 > 
 > 
 > 
 >             email addresses included in the To and CC lines. (Feel free to cut this
 > 
 > 
 > 
 >             introductory paragraph, however.)
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             Please refer to https://urldefense.proofpoint.com/v2/url?u=https-
 > 3A__www.ietf.org_iesg_statement_discuss-2Dcriteria.html&d=DwIGaQ&c=LFYZ-
 > o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=lB8O9Nd8E9rpRoJj0YX-
 > mV3Tpp8iWGOSIp_fkDPkMuA&s=LvqOOWwzZ-3P6mF9xQUGj2HWklodlOlWO94fprhgwc8&e=
 > 
 > 
 > 
 >             for more information about IESG DISCUSS and COMMENT positions.
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             The document, along with other ballot positions, can be found here:
 > 
 > 
 > 
 >             https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-
 > 2Drtgwg-2Dbackoff-2Dalgo_&d=DwIGaQ&c=LFYZ-
 > o9_HUMeMTSQicvjIg&r=6UhGpW9lwi9dM7jYlxXD8w&m=lB8O9Nd8E9rpRoJj0YX-
 > mV3Tpp8iWGOSIp_fkDPkMuA&s=YnZA5VGqF0T8BAOlFKka0ckWFUhUDHd0sILBbPRRaeU&
 > e=
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             ----------------------------------------------------------------------
 > 
 > 
 > 
 >             DISCUSS:
 > 
 > 
 > 
 >             ----------------------------------------------------------------------
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             While I agree with Alvaro's concerns, my concern is the appropriateness of this document
 > as PS.
 > 
 > 
 > 
 >             This document should have a similar status as RFC6976 (Informational) which also
 > provided a
 > 
 > 
 > 
 >             mechanism that prevented transient loops saying "the mechanisms described in this
 > 
 > 
 > 
 >             document are purely illustrative of the general approach and do not constitute a protocol
 > 
 > 
 > 
 >             specification". Especially as this document compares itself to RFC6976, saying RFC6976 is
 > a
 > 
 > 
 > 
 >             "full solution".
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 >             With a change of status to Informational, this document would be better
 > 
 > 
 > 
 >             scoped as providing guidance vs. a specification.
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > 
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 > 


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