Impact of Shortest Path First (SPF) Trigger and Delay Strategies on IGP Micro-loops
draft-ietf-rtgwg-spf-uloop-pb-statement-10

[Ballot comment]
Thank you for this clear and thoughtful document!  I only have nit-level
editorial suggestions, which you should feel free to accept or ignore as
you desire.

Section 1

  For non standardized timers, implementations are free to implement
  them in any way.  For some standardized timers, we can also see that
  rather than using static configurable values for such timer,
  implementations may offer dynamically adjusted timers to help
  controlling the churn.

nit: "help control"

  This document will present why it sounds important for service
  providers to have consistent implementations of Link State protocols
  across vendors.  [...]

nit: "why it sounds important" has a connotation that it's not actually
important, which I don't think is the position of anyone here.  So maybe
"why it is important" or "will present reasons for service providers to".

  [RFC8405] defines a solution that satisfies this problem statement
  and this document captures the reasoning of the provided solution.

nit: maybe this is just my personal background, but I am used to seeing
"satisfy" used with requirements but "address" with problems.  It was also
unclear to me that 8405 is a complete solution; if I remember correctly it
is only claiming to reduce the number of micro-loops and not to completely
eliminate them.  In that case, maybe "partially addresses" is better.

Section 2

  o  the delay of failure notification: the more E is advised of the
      failure later than S, the more a micro-loop may have a chance to
      appear.

nit: I'd suggest "the greater the time gap between E and S being advised of
the failure"

  o  the SPF computation time: mostly a matter of CPU power and
      optimizations like incremental SPF.  If S computes its SPF faster
      than E, there is a chance for a micro-loop to appear.  CPUs are
      today fast enough to consider SPF computation time as negligible
      (on the order of milliseconds in a large network).

side note: this makes me realize my own ignorance -- about how long would a
micro-loop typically be active for?  Also milliseconds?

  o  the SPF computation order: an SPF trigger can be common to
      multiple IGP areas or levels (e.g., IS-IS Level1/Level2) or for

nit: My first time reading this I misread it to mean scaling or distance,
as in "first-order"/"second-order"/etc.  Perhaps it's clearer to use
"ordering".

  plays a significant role.  As the number of IGP events increase, the
  delta between SPF delay values used by routers becomes significant
  and the major part (especially when one router increases its timer

nit: I offer "dominating factor" as a potential alternative for "major
part".

  However, for micro-loops, what's matter is not the total time, but

nit: "what matters"

Section 3

  may only run IP reachability computation instead) if the advertised

nit: "an IP reachability computation"

Section 4.2

Isn't the base of the exponent also a parameter that needs to be specified
(or is 2 the universally chosen base)?

Section 7

I suppose that things like "micro-loops can cause out-of-order delivery"
are universally-enough known that we don't need to be tempted to abuse this
document as a general dumping ground for security-relevant statements about
micro-loops.

[Ballot comment]
Thanks for using the updated RFC 8174 boilerplate instead of that from 2119. However, IDNits claims that there are no normative keywords at all, so is the boilerplate needed in the first place?

[Ballot comment]
  [RFC8405] defines a solution that satisfies this problem statement
  and this document captures the reasoning of the provided solution.

It's shame that this work wasn't published before rfc8405, or at least with it.  It is also sad that, while this document claims that it "captures the reasoning of the provided solution", rfc8405 mentions it just in passing...

I believe the analysis is valuable, and know that the WG has put significant effort on it, so I am not questioning its publication in the IETF Stream.

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Functions Operator has reviewed draft-ietf-rtgwg-spf-uloop-pb-statement-08, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any registry actions.

While it's often helpful for a document's IANA Considerations section to remain in place upon publication even if there are no actions, if the authors strongly prefer to remove it, we do not object.

If this assessment is not accurate, please respond as soon as possible.

Thank you,

Sabrina Tanamal
Senior IANA Services Specialist

The following Last Call announcement was sent out (ends 2018-12-18):

From: The IESG
To: IETF-Announce
CC: draft-ietf-rtgwg-spf-uloop-pb-statement@ietf.org, chrisbowers.ietf@gmail.com, rtgwg-chairs@ietf.org, Chris Bowers , martin.vigoureux@nokia.com, rtgwg@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Link State protocols SPF trigger and delay algorithm impact on IGP micro-loops) to Informational RFC


The IESG has received a request from the Routing Area Working Group WG
(rtgwg) to consider the following document: - 'Link State protocols SPF
trigger and delay algorithm impact on IGP
  micro-loops'
  as Informational RFC

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2018-12-18. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the beginning of
the Subject line to allow automated sorting.

Abstract


  A micro-loop is a packet forwarding loop that may occur transiently
  among two or more routers in a hop-by-hop packet forwarding paradigm.

  In this document, we are trying to analyze the impact of using
  different Link State IGP (Interior Gateway Protocol) implementations
  in a single network, with respect to micro-loops.  The analysis is
  focused on the SPF (Shortest Path First) delay algorithm.





The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-rtgwg-spf-uloop-pb-statement/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-rtgwg-spf-uloop-pb-statement/ballot/


No IPR declarations have been submitted directly on this I-D.

As required by RFC 4858, this is the current template for the Document
Shepherd Write-Up.

Changes are expected over time. This version is dated 24 February 2012.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

Informational is requested as indicated in the title page header.

(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

Micro-loops are transient forwarding loops that can occur among
routers using hop-by-hop forwarding. This document analyzes
the impact of using different Link State IGP implementations
in a single network with respect to micro-loops. 
The analysis focuses on the SPF triggers and SPF delay algorithms.

Working Group Summary

The final version of the document has strong consensus in the WG. Input
from the WG was incorporated in the document.

Document Quality

The document is of high quality.

Two Routing Area Directorate reviews were done.  The first was
done by Mike Shand around the time of working group adoption.
This review pointed out some issues related to terminology and phrasing,
as well as a generalization about the size of networks.  These
issues were addressed by the authors.

The main issue raised by the second review (done by Tomonori Takeda)
was the fact the document was classified as Standards Track.  This
was addressed by changing it to Informational.


Personnel

  Document Shepherd: Chris Bowers
  Responsible Area Director: Martin Vigoureux

(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

The document that passed WGLC still needed some editorial
work, so the Document Shepherd provided the following feedback.
https://mailarchive.ietf.org/arch/msg/rtgwg/NLThRm6Jz1JDC_VKXTrNsozPl1M

This resulted in the publication of version 7, which addressed
the editorial issues.

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

The Document Shepherd has no concerns in this respect.

(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

No additional review beyond that already done by the Routing Area
Directorate is needed.

(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the WG has discussed those issues and
has indicated that it still wishes to advance the document, detail those
concerns here.

The Document Shepherd has no concerns in this respect.

(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

Each author has indicated that they are not aware of any relevant IPR.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

No IPR disclosure has been filed that references this document.

(9) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with others
being silent, or does the WG as a whole understand and agree with it? 

The final version of the document has strong consensus from the WG.

(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in separate
email messages to the Responsible Area Director. (It should be in a
separate email because this questionnaire is publicly available.)

No.

(11) Identify any ID nits the Document Shepherd has found in this
document. (See https://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

The following two warnings should be addresed in a future revision.

  == The document doesn't use any RFC 2119 keywords, yet seems to have RFC
    2119 boilerplate text.

  == Outdated reference: draft-ietf-rtgwg-uloop-delay has been published as
    RFC 8333

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

No additional formal reviews are required based on the document content.

(13) Have all references within this document been identified as
either normative or informative?

All references have been identified as normative or informative.
There are currently 4 normative references.  Since this is
an informational document, it might make sense to classify some
or all of those references as in informative.

(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

There are no normative references in an unclear state.

(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

There are no downward normative references.

(16) Will publication of this document change the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

The publication of this document will not change the status of any
existing RFCs.

(17) Describe the Document Shepherd's review of the IANA considerations
section, especially with regard to its consistency with the body of the
document. Confirm that all protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

There are no IANA considerations.

(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

There are no new IANA registries.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.

No sections of the document are written in a formal language.