Common Interval Support in Bidirectional Forwarding Detection
draft-ietf-bfd-intervals-05

Received changes through RFC Editor sync (changed abstract to 'Bidirectional Forwarding Detection (BFD) requires that messages be transmitted at regular intervals and provides a way to negotiate the interval used by BFD peers. Some BFD implementations may be restricted to only support several interval values. When such BFD implementations speak to each other, there is a possibility of two sides not being able to find a common value for the interval to run BFD sessions.

This document updates RFC 5880 by defining a small set of interval values for BFD that we call "Common Intervals" and recommends implementations to support the defined intervals. This solves the problem of finding an interval value that both BFD speakers can support while allowing a simplified implementation as seen for hardware-based BFD. It does not restrict an implementation from supporting more intervals in addition to the Common Intervals.')

[Ballot comment]
We came to the conclusion that Informational (without 2119 language) and updating 5880 were an appropriate state for this document. Thanks for the DISCUSSion.

[Ballot comment]
I support Pete's DISCUSS. However, I won't be able to attend the IESG telechat, so I'll trust Pete.

I had an interesting discussion at lunch time with Jeff Haas (during the NETMOD interim). The WG is afraid that, if that future RFC is standards track, the customers will require vendors to implement those Common Interval values is. And, for example, 3.3msec might not always be possible.

I'm not convinced that playing this "informational" trick because of that reason is reasonable.
However, this solution might be simple:
OLD:

  a BFD
    implementation SHOULD support all values in the set of Common
    Interval values which are equal to or larger than the fastest, i.e.
    lowest, interval the particular BFD implementation supports.

NEW:
  a BFD
    implementation should support all values in the set of Common
    Interval values which are equal to or larger than the fastest, i.e.
    lowest, interval the particular BFD implementation supports.

Anyway, this SHOULD was not targeting bits on the wire.

[Ballot comment]
I agree with Pete that it would be better for this to be Standards Track, both from a process-wonk perspective, and from the perspective of actually getting implementers to support these intervals.

Also, since I expect many implementers will be skimming this to find out the values (rather than read the explanatory text), it would be helpful to move the numbers up front, put them in a table / bulletted list, or both.

[Ballot discuss]
I do not expect to hold this DISCUSSion for very long, but I do want to have it. The shepherd writeup says:

  This draft is being targeted for Informational status.  While the
  draft recommends a number of timer values, they are suggested for
  interoperability while not mandating that any particular value be
  supported.

  There was discussion on the mailing list that while the draft was
  listed as Informational that some customers were likely to take the
  RFC as a base set of standard values - thus a de facto standard.
  Consensus of the list seemed to judge that this was okay and provided
  values that implementors may want to look at targeting as part of
  their implementations.

First of all, the values defined/specified (cf. Alia: not "proposed") in this document are described as "SHOULD support all values in the set". That seems perfectly reasonable, but that's a protocol requirement. ("SHOULD" does not mean "OPTIONAL".) Further, the WG itself is clear that this is likely to turn into a de facto standard anyway. IETF standards are voluntary anyway. If the BFD community has consensus that this is something that SHOULD be supported by 5880 implementations and that implementers are going to do it anyway, why not call it a Proposed Standard, mark it as updating 5880, and move along?

[Ballot comment]
Language in the draft should change from proposed to definitive. 

For example, in Sec 3,

"The proposed set of Common Interval values is: 3.3msec, 10msec,
  20msec, 50msec, 100msec and 1sec.

  In addition support for 10sec interval together with multiplier
  values up to 255 is recommended to support graceful restart.
"

could become:

"This document defines the set of Common Interval values to
be exactly: ...."

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-bfd-intervals-03, which is currently in Last Call, and has the following comments:

We understand that, upon approval of this document, there are no IANA Actions that need completion.

While it is helpful for the IANA Considerations section of the document to remain in place upon publication, if the authors prefer to remove it, IANA doesn't object.

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

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Common Interval Support in BFD) to Informational RFC


The IESG has received a request from the Bidirectional Forwarding
Detection WG (bfd) to consider the following document:
- 'Common Interval Support in BFD'
  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 2014-09-01. 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


  BFD requires that messages are transmitted at regular intervals and
  provides a way to negotiate the interval used by BFD peers.  Some BFD
  implementations may be restricted to only support several interval
  values.  When such BFD implementations speak to each other, there is
  a possibility of two sides not being able to find a common interval
  value to run BFD sessions.

  This document defines a small set of interval values for BFD that we
  call "Common intervals", and recommends implementations to support
  the defined intervals.  This solves the problem of finding an
  interval value that both BFD speakers can support while allowing a
  simplified implementation as seen for hardware-based BFD.  It does
  not restrict an implementation from supporting more intervals in
  addition to the Common intervals.


The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-bfd-intervals/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-bfd-intervals/ballot/


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

AD Review
=====

Hello,

If you considered that Jeff helped find the line between "exact" and
"pedantic" then you may rest assured that I have crossed it (in one
direction or the other).

This is my usual AD review of your document to advance the publication
request. It is a short document (Hooray!) and is perfectly clear.
Nevertheless, I have picked a few holes for style and clarity. Please
feel free to dispute these points with me if you like. Until then, or
until I see a revised version of the document, I have placed the I-D
in "Revised I-D Needed" state.

Thanks for your work,
Adrian

===

It seems to me that the main benefit in this work is to improve the
chances of interoperability between hardware implementations that need
to select a hard-wired subset of interval values at build time.  There
are two points arising from this:

- You should recommend that implementations that can do so, should
  support a superset of the values identified here, and suggest that
  implementations try to support a considerably more flexible set of
  values to facilitate operator control of the responsiveness and
  scalability of BFD.

- You should observe that not all implementations of BFD are intended
  to interoperate. This may be particularly true for certain hardware
  implementations (e.g., BFD for MPLS-TP and BFD for Ethernet LAG).
  This *might* have an impact on whether every implementation has to
  support every value in the set. Whether or not is does have an impact
  could usefully be commented in the document.

---

The Abstract might benefit from one line saying what an "interval value"
is. Something like,

  "BFD requires that messages are transmitted at well-known intervals
    and provides a way to negotiate the interval used by BFD peers."

---

I only see one use of RFC 2119 language. Section 3 has

  In technical terms the requirement is as follows: a BFD
  implementation SHOULD support all values in the set of Common
  interval values which are equal to or larger than the fastest, i.e.
  lowest, interval the particular BFD implementation supports.

Maybe you don't actually need uppercase "SHOULD" and then you could
drop the "Requirements Language" paragraph.

---

Section 1

  number of BFD sessions in increasing.

s/in/is/

---

Section 3

  This document is not adding new requirements with respect to how
  exact a timer value must be implemented.

I think you don't mean "the precision with which a timer value must be
implemented", but if you do, please change to say that. Otherwise, I
suggest

  This document is not adding new requirements with respect to how
  a timer value must be implemented.

---

Section 3

  How is the "Common interval set" used exactly?  In the example above,
  vendor "A" has a fastest interval of 10msec and thus would be
  required to support all intervals in the common set that are equal or
  larger than 10msec, i.e. it would support 10msec, 20msec, 50msec,
  100msec, 1sec.  Vendor "B" has a fastest interval of 20msec and thus
  would need to support 20msec, 50msec, 100msec and 1sec.  As long as
  this requirement is met for the common set of values, then both
  vendor "A" and "B" are free to support additional values outside of
  the common set.

I disagree! In the example you have used, implementation "A" will try to
set up the session with 10msec and implementation "B" will support that
interval because it is in the set.

I think that, to give the example meaning you need to have "A" initially
suggest a value that is not in the set, for example 15msec. Then "B"
will respond with 20msec and that value will be chosen because it is in
the set.

---

Section 5

This is rally to check with you. Can influencing the interval value used
by a BFD session be used as part of an attack? For example, can forcing
the transmission time to be slower make it harder to detect naughtiness?
And can forcing the interval to be faster help cause DoS? If so, does
limiting the set of available values make attacks easier?

: Document Writeup for Working Group Documents
:
: 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?

This draft is being targeted for Informational status.  While the draft
recommends a number of timer values, they are suggested for
interoperability while not mandating that any particular value be
supported.

There was discussion on the mailing list that while the draft was listed
as Informational that some customers were likely to take the RFC as a
base set of standard values - thus a de facto standard.  Consensus of
the list seemed to judge that this was okay and provided values that
implementors may want to look at targeting as part of their
implementations.

: (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:

[From the abstract]

  Some BFD implementations may be restricted to only support several
  interval values.  When such BFD implementations speak to each other,
  there is a possibility of two sides not being able to find a common
  interval value to run BFD sessions.

  This document defines a small set of interval values for BFD that we
  call "Common intervals", and recommends implementations to support
  the defined intervals.  This solves the problem of finding an
  interval value that both BFD speakers can support while allowing a
  simplified implementation as seen for hardware-based BFD.  It does
  not restrict an implementation from supporting more intervals in
  addition to the Common intervals.

: 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?

Discussion in the working group among known implementors of BFD was
relatively quiet but supportive of this document.  The only discussion
that generated any significant amount of "noise" was the discussion of
whether these well known common intervals should have an IANA registry
to permit the maintenance of this document without requiring a RFC
revision.  The consensus of that discussion was that an IANA registry
was not desired.

: 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?

Multiple implementations support the full range of documented values in
either hardware or software, depending on the implementation.  The only
value that doesn't have very wide support is the 3.3ms value, but
support for this value seems to be becoming more common.

: Personnel:
:
: Who is the Document Shepherd? Who is the Responsible Area Director?

Document Shepherd: Jeffrey Haas
Responsible Area Director: Adrian Farrel

: (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.

A thorough review of this document was done by the shepherd and the
document is judged to be of good quality and ready for publication.
Prior versions of this document were previously polled against known
implementations ot find out if the intervals present in this document
were supported.

: (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.

There are no such 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?

This document simply notes common intervals that may be used with BFD
(RFC 5880) sessions.  No new IPR would be relevant.

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

Not applicable.

: (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?

Generally good support among known implementors of the protocol.  As is
typically the case for the BFD working group, a small core group is
responsible for the majority of the review and also the text.

: (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.

The draft checks clean.

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

Not applicable.

: (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 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 such changes.

: (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 described above, no new requests are made to IANA.

: (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.

Not applicable.

-- Jeff