Updates to the Fast Reroute Procedures for Co-routed Associated Bidirectional Label Switched Paths (LSPs)
draft-ietf-teas-assoc-corouted-bidir-frr-07

[Ballot comment]

Thanks for the work everyone did on this document.

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Please expand "LSP" in the abstract.

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§3.3:

>  In this example, the mid-point node D may mistakenly associate LSP1
>  with the reverse LSP4 instead of the reverse LSP3 due to the matching
>  (Extended) ASSOCIATION Objects.

This doesn't seem right to me. LSP1 and LSP3 appear to be forward direction,
while LSP2 and LSP4 appear to be reverse direction. It's also not clear how LSP1
would be associated with LSP3 in this scenario, which is what this sentence
seems to be saying might happen.

Did this mean to say "...instead of the reverse LSP2..."?

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§4.2:

>  In order to associate the LSPs unambiguously at a mid-point node (see
>  Figure 3), the endpoint node MUST signal Extended ASSOCIATION Object
>  and add unique Extended Association ID for each associated forward
>  and reverse LSP pair forming the bidirectional LSP.  An endpoint node
>  MAY set the Extended Association ID to the value shown in Appendix A.

This phrasing is very confusing, as it implies that Appendix A is going to
contain a value that can be used as an ID (which would be at odds with
"unique"). Appendix A contains a format, not a value. I think what you mean is:

"...MAY set the Extended Association ID to a value formatted according to the
structure shown in Appendix A."

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Appendix A:

>  Extended Association ID in the Extended ASSOCIATION Object [RFC6780]
>  can be set to the value shown in the following example to uniquely

Same comment as above regarding the distinction between "value" and "format".

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Appendix A:

>    0                  1                  2                  3
>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |                    IPv4 LSP Source Address                    |
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |          Reserved            |            LSP-ID            |
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

What are implementors expected to set the "Reserved" bytes to?

[Ballot comment]
How does the unidirectional link failure logic and the revertive logic
interact?  That is, in the unidirectional failure case a node should be
detecting that there is a failure case and rerouting reverse traffic onto
the protection path to match the forward path.  But a node in the process
of reverting back on to the primary path (before its counterpart in the
other direction) would seem to observe the same packet/path behavior as in
the case of a unidirectional link failure.  Do we need to rely on the
flooding of link status information to differentiate between these cases?

Are the state-keeping and resource consumption burdens large for the
midpoint nodes that now must correlate whether they see traffic on
original/protection paths for associated flows?  (E.g., Section 4.1.3's
"when it receives the un-modified RSVP path messages and traffic".)
It seems like it should just be a linear scaling factor at worst, with no
real path to an attack, but perhaps there are security considerations
relating to router capacity.

Section 2

  In packet transport networks, there are requirements where the
  reverse LSP of a bidirectional LSP needs to follow the same path as
  its forward LSP [RFC6373].  [...]

Does this need a qualifier (e.g., "some packet transport networks" or
"there are sometimes requirements")?


Section 3.2

  tunnel S (on path B-F-G-D) to reach downstream MP node D whereas the
  upstream PLR node C reroute the protected reverse LSP2 traffic over
  the bypass tunnel N (on path C-I-H-A) to reach the upstream MP node
  A.  [...]

nit: "reroutes"

Section 4.1.1

  As shown in Figure 2, when using a node protection bypass tunnel with
  protected co-routed LSPs, asymmetry of paths can occur in the forward
  and reverse directions after a link failure [RFC8271].  In order to
  restore co-routing, the downstream MP node D (acting as an upstream
  PLR) SHOULD trigger the procedure to restore co-routing and reroute
  the protected reverse LSP2 RSVP Path messages and traffic over the
  bypass tunnel S (on path D-G-F-B) to the upstream MP node B upon

Why is this only a SHOULD?

Section 4.2

                                                        An endpoint node
  MAY set the Extended Association ID to the value shown in Appendix A.

The contents of Appendix A do not include a distinguished single value, but
rather a data structure, so I think that a phrase other than "to the
value" should be used.

  o  For double-sided provisioned bidirectional LSPs [RFC7551], both
      endpoints need to ensure that the bidirectional LSP has a unique
      Extended ASSOCIATION Object for each forward and reverse LSP pair
      by selecting appropriate unique Extended Association IDs signaled
      by them.

How does this signalling/selection process get the two endpoints to agree
on the same value?

Appendix A

(Again, "to the value" is not appropriate to describe the general format.
Perhaps, "to a value using the format".)

Please also explicitly describe the semantics of the "Reserved" field(s)
(i.e., set to zero on transmission and ignored on receipt).

[Ballot comment]
I agree with Ben's comment about the unconventional document structure. I'm not an expert, but I think I understood the Introduction well enough to get through it before needing to look at the terminology for precise meanings, and it does seem odd compared to the vast majority of RFCs I've reviewed, so somewhat disorienting for readers.

[Ballot comment]
Thanks for the work on this!

I just have one strictly editorial comment:

I found it odd that the introduction doesn't occur until section 2.  I think section 1 would make more sense if I had had the context from the introduction when reading it.

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

The IANA Functions Operator has reviewed draft-ietf-teas-assoc-corouted-bidir-frr-06, 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 2018-09-20):

From: The IESG
To: IETF-Announce
CC: Vishnu Beeram , db3546@att.com, teas-chairs@ietf.org, draft-ietf-teas-assoc-corouted-bidir-frr@ietf.org, teas@ietf.org, vishnupavan@gmail.com
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Updates to the Fast Reroute Procedures for Co-routed Associated Bidirectional Label Switched Paths (LSPs)) to Proposed Standard


The IESG has received a request from the Traffic Engineering Architecture and
Signaling WG (teas) to consider the following document: - 'Updates to the
Fast Reroute Procedures for Co-routed Associated
  Bidirectional Label Switched Paths (LSPs)'
  as Proposed Standard

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 2018-09-20. 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


  Resource Reservation Protocol (RSVP) association signaling can be
  used to bind two unidirectional LSPs into an associated bidirectional
  LSP.  When an associated bidirectional LSP is co-routed, the reverse
  LSP follows the same path as its forward LSP.  This document updates
  the Fast Reroute (FRR) procedures defined in RFC 4090 to support both
  single-sided and double-sided provisioned associated bidirectional
  LSPs.  This document also updates the procedure for associating two
  reverse LSPs defined in RFC 7551 to support co-routed bidirectional
  LSPs.  The FRR procedures can ensure that for the co-routed LSPs,
  traffic flows on co-routed paths in the forward and reverse
  directions after a failure event.





The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-teas-assoc-corouted-bidir-frr/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-teas-assoc-corouted-bidir-frr/ballot/

The following IPR Declarations may be related to this I-D:

  https://datatracker.ietf.org/ipr/2781/

> 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)? 

Standards Track.

> Why is this the proper type of RFC? 


Standards Track is apt because the document updates RSVP-TE procedures.


> Is this type of RFC indicated in the title page header?

Yes.

> (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

>  Relevant content can frequently be found in the abstract
>  and/or introduction of the document. If not, this may be
>  an indication that there are deficiencies in the abstract
>  or introduction.

  Resource Reservation Protocol (RSVP) association signaling can be
  used to bind two unidirectional LSPs into an associated bidirectional
  LSP.  When an associated bidirectional LSP is co-routed, the reverse
  LSP follows the same path as its forward LSP.  This document updates
  the Fast Reroute (FRR) procedures defined in RFC 4090 to support both
  single-sided and double-sided provisioned associated bidirectional
  LSPs.  This document also updates the procedure for associating two
  reverse LSPs defined in RFC 7551 to support co-routed bidirectional
  LSPs.  The FRR procedures can ensure that for the co-routed LSPs,
  traffic flows on co-routed paths in the forward and reverse
  directions after a failure event.

> Working Group Summary
>
>  Was there anything in WG process that is worth noting? For
>  example, was there controversy about particular points or
>  were there decisions where the consensus was particularly
>  rough?

The progress of the document through the WG has been smooth.


> Document Quality

>  Are there existing implementations of the protocol? Have a
>  significant number of vendors indicated their plan to
>  implement the specification? Are there any reviewers that
>  merit special mention as having done a thorough review,
>  e.g., one that resulted in important changes or a
>  conclusion that the document had no substantive issues? If
>  there was a MIB Doctor, Media Type or other expert review,
>  what was its course (briefly)? In the case of a Media Type
>  review, on what date was the request posted?

The base (G)MPLS RSVP protocol has been implemented. The procedures
discussed in this document are compatible with earlier implementations.
While there have been no public statements on implementation, the
authors are from multiple vendors, and implementation is expected.

> Personnel
>
>  Who is the Document Shepherd?

Vishnu Pavan Beeram

> Who is the Responsible Area Director?

Deborah Brungard

> (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 Shepherd has reviewed the document as it has progressed
through the WG. The Shepherd believes this document is ready for publication.

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

No.

> (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?

No.

> If so, describe the review that took place.

N/A.


> (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.

No specific concerns.

> (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.

Yes, see thread -
https://mailarchive.ietf.org/arch/msg/teas/qeSHglFQ88a2GPBrgTq47n45knc


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

Yes, an IPR disclosure has been filed that references this document 
(see https://datatracker.ietf.org/ipr/2781/).There was no WG discussion
regarding the IPR disclosures.


> (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? 

Solid among those who are interested. "strong concurrence of a few
individuals, with others being silent" is a reasonable
characterization.

> (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 discontent seen.

> (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 document passes ID nits.

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

N/A.

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

Yes.

> (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?

No.

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

No.

> (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.

This document updates RFCs 4090 and 7551. Those are listed on the title
page header, listed in the abstract and discussed in the introduction.

> (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).

The IANA section was fully reviewed by the document shepherd. There are
no protocol extensions introduced by this document.


> (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.

None.

> (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.

N/A.