TRILL: Resilient Distribution Trees
draft-ietf-trill-resilient-trees-09

As is customary, I have done my AD review of draft-ietf-trill-resilient-trees-08.
First, I would like to thank the authors Mingui, Tissa, Janardhanan, Ayan, and Anoop
for their work on this document. 

Unfortunately, I have several serious concerns about this document.

First, and most importantly, there is not a clear and mandatory algorithm for computing the backup distribution trees that is given. Sec 3.2.1.1 provides a recommendation that is still not fully specified.
I do see the idea that the root of a backup distribution tree need not be the same as the root of the primary distribution tree - but I see no indication of what decides which the root is.  Perhaps it is the root of the primary distribution tree?    What is computing the backup distribution trees?  My assumption is that each RBridge does.  Can  a backup distribution tree be associated with only one primary distribution tree?

Second, I don't believe that the suggested algorithm of raising the link costs for links used in a primary distribution tree will work to find maximally disparate paths.  Consider the simpler case with Suurballe's algorithm  (https://en.wikipedia.org/wiki/Suurballe's_algorithm) that is just looking for 2 disparate paths.  In that example, the shortest path is A-B-D-F which gives no disjoint path between A and F - but different pairs of paths are possible.

Obviously MRT (RFC7811) solves this issue - and it is possible to have different roots for the RED and BLUE trees by simply creating a proxy node that attaches to the potential roots.  There may be a bit of work to be done - but it is similar to other proxy nodes used in RFC7811 and RFC7812.

You may have different solutions - and that is fine - but failing to fully specify an algorithm and having what is specified not work is not ok.

Third, pulling back and clearly explaining the different pieces of this technology is badly needed.  For instance:
    (a) The root for a multicast distribution tree computes a backup distribution tree and identifies the root to use.
    (b) A PLR determines the backup distribution tree (how?)
    (c) Each RBridge computes its part of the backup distribution tree - by pinning specific links into the backup distribution tree as advertised as affinity links (??)
    (d) Is traffic looked for on the backup distribution tree?  How does a merge point/receiver make that decision?

Some of these details are in the draft - but it is quite hard to pull out clearly.

Are there any implementations of this draft?

PROTO for draft-ietf-trill-resilient-trees

(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?

Proposed Standard as indicated on the title page. This draft updates
the base TRILL standard.

(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:

In TRILL multicast data forwarding is based on IS-IS link state
routing.  Distribution trees are computed based on the link state
information through Shortest Path First calculation. When a link on
the distribution tree fails, with the TRILL base standard a
campus-wide reconvergence takes place that can be time consuming and
may cause disruption to the ongoing multicast service. This document
specifies how to build backup distribution trees to protect links on
a primary distribution tree.

  Working Group Summary:

Nothing particularly notable. There was consensus for advancing the
draft.

  Document Quality:

The document has received thorough review and is of high quality.

  Personnel:
Document Shepherd:  Donald Eastlake
Responsible Area Director:  Alia Atlas

(3) Briefly describe the review of this document that was performed
    by the Document Shepherd.

See Shepherd review at
https://www.ietf.org/mail-archive/web/trill/current/msg07759.html
The comments there have been resolved in the current -08 draft.

(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.

Routing QA review done 9/8/16 by Loa Andersson. Loa has confirms that
all his comments have been resolved.

(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 special 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?

Disclosure messages posted by all authors. See emails:

Mingui Zhang:
  https://www.ietf.org/mail-archive/web/trill/current/msg07494.html
Pathangui Janardhanan
  https://www.ietf.org/mail-archive/web/trill/current/msg07492.html
Ayan Banerjee:
  https://www.ietf.org/mail-archive/web/trill/current/msg07491.html
Anoop Ghanwani:
  https://www.ietf.org/mail-archive/web/trill/current/msg07489.html
Tissa Senevirathne:
  https://www.ietf.org/mail-archive/web/trill/current/msg07490.html

(8) Has an IPR disclosure been filed that references this document?
    If so, summarize any WG discussion and conclusion regarding the
    IPR disclosures.
No.

(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?

There has been sufficient support for the this draft at meetings and
on the mailing list from a variety of participants.

(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 http://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.

No such formal review required.

(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?

There is a normative reference to draft-ietf-trill-p2mp-bfd which has
been judged to have WG consensus and is expected to advance soon.

(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 normative downward 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?

This document updates RFC 6325 as specified in Section 5.3.1.

(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 Considerations were reviewed as part of the Shepherd review
of the document. All newly allocated values are indicated by "tbd"
followed by a digit and all appear to be properly allocated in the
IANA Considerations section.

(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.

No new registries are created.

(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 such automated reviews required.