Recommendations for RSVP-TE and Segment Routing (SR) Label Switched Path (LSP) Coexistence
draft-ietf-teas-sr-rsvp-coexistence-rec-04

[Ballot comment]
Most of my comments have already been made by others. I have only a couple of minor comments remaining:

§1:
-It seems kind of weird to mix "requirements" and "assumptions" in the same list.
- Item 4: The "MAY" seems like a statement of fact, not permission.

[Ballot comment]
TED/its expansion should be introduced in the Introduction, not the
Abstract, since the Abstract and the rest of the document must be
able to be read in a standalone manner.


In line with Alvaro's comment, I would suggest moving Sections 3.1
through 3.4 into a new parent section "Discarded Options" or
similarly-named.


Section 3.5

  [...] It is RECOMMENDED that the IGP-TE update
  threshold SHOULD be lower in order to flood unreserved bandwidth
  updates often.

Lower than what?


Section 7

It feels odd to say that these "do not require any new security
considerations" and then go and list some new security
considerations.  I would suggest something like "The security
considerations of each protocol are unaffected by the presence of
the other, so only the interactions of the TED consistency solution
with the individual protocols needs to be considered."

I would probably also want to expand the text a bit, noting that:

A hijacked SR traffic stream could potentially cause disruption to
RSVP-TE LSPs in two ways: directly, but consuming sufficient
bandwidth to cause traffic loss, and indirectly, by consuming
sufficient traffic to result in the TED consistency solution
proposed in this document reducing the bandwidth available to
RSVP-TE paths.  The former is possible whenever RSVP-TE and SR
traffic share links, independently of whether this specification is
in use; the latter is new behavior with this specifciation but is
seen as preferrable to the alternative, since the impact to RSVP-TE
traffic can be controlled and paths re-routed.  However, some latent
risk of disruption remains because this specification is a reactive
protcol, relying on taking measurements and only adopting to new
traffic flows after the measurement period.  The finite duration of
the measurement window leaves open a period of potential disruption
before remediation can be applied.


Appendix A

This guidance seems like it could be (very) roughly characterized as
"these are the ranges of values that are not insane to use".  Is it
possible to give more precise/active guidance, such as (taking a
wild guess) "Values between 0.9 and 1.1 allow for taking accunt of
estimated future traffic growth during the current measurement
period while reducing the risk of leaving large amounts of bandwidth
underutilized.  The measurement period should be smaller than a
minute in order for this tight of a growth window to make sense."

[Ballot comment]
(1) The Abstract says that this document provides "solution options" -- it would be very nice if a recommendation (or at least general guidance) was provided by the authors.  This point was brought up in the OpsDir review [1], to which the authors replied:

  "The intent behind the recommendations is to not take a position on which solution is preferable. All solutions are valid but some do not satisfy all the requirements. However, if a solution is acceptable (based on their deployment of SR and RSVP and knowing which requirements are not satisfied) for an operator then such a solution can be chosen. "

That seems like a reasonable answer.  It would be good if, at least, text to the effect was included in the document.

(2) Given, from the text above, that not all requirements may be as important in a specific deployment, I find the use of rfc2119 language to describe them (in the Introduction) confusing and inappropriate.  Please consider not using Normative text in that section.

(3) While wondering whether there was a recommendation coming out of this document, I looked for other documents referencing it, and found 1: draft-ietf-mpls-rsvp-shared-labels ("Signaling RSVP-TE tunnels on a shared MPLS forwarding plane").  I realize that the topic is not exactly a match, but this sentence is included in it: "The RSVP-TE tunnels that use this shared forwarding plane can co-exist with MPLS-SR LSPs [I-D.ietf-spring-segment-routing-mpls] as described in [I-D.ietf-teas-sr-rsvp-coexistence-rec]."

I took a very quick look at draft-ietf-mpls-rsvp-shared-labels and the mechanism described there didn't look like any of the options described here.  Is the mechanism described in draft-ietf-mpls-rsvp-shared-labels an option to the problem addressed in this document?  If so, is it worth including a short description?  If not, then the sentence above sounds misleading.

[I realize I may be asking questions about a different document...but I'm taking the license given that the editor for this document is also an author in the other one. ;-) ]

(4) Nits:

(4.1) This text in the Abstract seems redundant: "In some instances, operators are also migrating existing services from RSVP-TE to SR LSPs...In other cases, services running on RSVP-TE might be migrated to run over SR."

(4.2) From §3.2:
  Note that it is not enough for the controller to just maintain the
  unified view of the available capacity, it must also perform the path
  computation for the RSVP-TE LSPs, as the reservations for the SR LSPs
  are not reflected in the TED.  This does not fit with assumption 2
  mentioned earlier.

Assumption 2 says that "Engines that compute RSVP-TE paths may have no knowledge of the existence of the SR paths in the same domain.", but in the scenario described here (where the controller "must also perform the path computation for the RSVP-TE LSPs"), then the assumption is not true as the controller would in fact have knowledge of the coexistence.  This is just a nit: I don't think the last sentence is accurate...

(4.3) This text is normatively redundant: "It is RECOMMENDED that the IGP-TE update threshold SHOULD be lower..."  RECOMMENDED and SHOULD mean the same thing.


[1] https://mailarchive.ietf.org/arch/msg/ietf/KwkK9VbeISPl9zgVmzdwLOB2FM0

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

The IANA Services Operator has reviewed draft-ietf-teas-sr-rsvp-coexistence-rec-02, 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 2018-04-20):

From: The IESG
To: IETF-Announce
CC: db3546@att.com, teas-chairs@ietf.org, teas@ietf.org, draft-ietf-teas-sr-rsvp-coexistence-rec@ietf.org, Lou Berger , lberger@labn.net
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Recommendations for RSVP-TE and Segment Routing LSP co-existence) to Informational RFC


The IESG has received a request from the Traffic Engineering Architecture and
Signaling WG (teas) to consider the following document: - 'Recommendations
for RSVP-TE and Segment Routing LSP co-existence'
  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 2018-04-20. 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


  Operators are looking to introduce services over Segment Routing (SR)
  LSPs in networks running Resource Reservation Protocol (RSVP-TE)
  LSPs.  In some instances, operators are also migrating existing
  services from RSVP-TE to SR LSPs.  For example, there might be
  certain services that are well suited for SR and need to co-exist
  with RSVP-TE in the same network.  In other cases, services running
  on RSVP-TE might be migrated to run over SR.  Such introduction or
  migration of traffic to SR might require co-existence with RSVP-TE in
  the same network for an extended period of time depending on the
  operator's intent.  The following document provides solution options
  for keeping the traffic engineering database (TED) consistent across
  the network, accounting for the different bandwidth utilization
  between SR and RSVP-TE.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-teas-sr-rsvp-coexistence-rec/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-teas-sr-rsvp-coexistence-rec/ballot/

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

  https://datatracker.ietf.org/ipr/2827/

> 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)?
Informational

> Why is this the proper type of RFC?

The document explores different approaches for handling SR and
RSVP-TE coexistence, and then concludes with a preferred approach.
I think it stops short of a required approach, which would make
BCP more appropriate.

> 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.

  The document provides solution options for keeping the traffic
  engineering database (TED) consistent across the network,
  accounting for the different bandwidth utilization between SR
  and RSVP-TE.

>
> 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?
>

Don't think there is anything particularly noteworthy.


> 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?
>

This is an informational document that has fairly niche
interests.  I think it has been adequately discussed in the WG
although I would certainly have preferred greater review and
participation.

> Personnel
>
>  Who is the Document Shepherd?
Lou Berger

> 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 shepherd reviewed the document multiple times as it progressed
through the WG as well as conducted a final shepherd review.  This
review yielded some minor comments that have been sent to the authors.

> (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? If so, describe the review that
> took place.

No

>
> (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.

None.

>
> (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.

>
> (8) Has an IPR disclosure been filed that references this document?
> If so, summarize any WG discussion and conclusion regarding the IPR
> disclosures.
>
indirectly, see
https://datatracker.ietf.org/ipr/search/?submit=draft&id=draft-ietf-teas-sr-rsvp-coexistence-rec

The working group was made aware of the IPR prior to WG adoption
and was reminded of the IPR (via a pre WG LC Poll) before LC.  No
other comments were made by WG participants.

> (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? 
>
strong concurrence of a few interested parties.

> (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.

no 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?

Yes, a reference to draft-ietf-spring-segment-routing is
normative.  This draft is being managed by the SPRING WG.  Frankly
this reference could be made informative as the whole document is
informative, but I also don't see an issue with the publication of
this draft being blocked by the reference either.

>
> (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.
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.

No, N/A.

>
>
> (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).

As an informational document without protocol changes, there is no
IANA impact.

>
> (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