SCTP-PF: A Quick Failover Algorithm for the Stream Control Transmission Protocol
draft-ietf-tsvwg-sctp-failover-16

[Ballot comment]
In addition to the 2119 issues that Ben has raised...

In Section 3.2 bullet 1:

        The RECOMMENDED value of PFMR is
        0, but other values MAY be used.

"SHOULD do X, but MAY do Y" makes no sense.  In this case, you can (should) just remove "but other values MAY be used".  You might instead say *why* 0 is recommended at a 2119 level (implying that it has interoperability implications).

In bullet 9, I found this to be oddly worded:

        A SCTP sender MAY clear the error counter
        and move a destination address back to active state if it has
        other information, than the acknowledgment, that uniquely
        determines which destination, among multiple destination
        addresses, the chunk reached.

Perhaps this?:

NEW
        A SCTP sender MAY clear the error counter
        and move a destination address back to active state if it has
        information other than the acknowledgment that uniquely
        determines which destination, among multiple destination
        addresses, the chunk reached.
END

[Ballot comment]


Thanks for a clearly written specification.

- Should this formally UPDATE 4960? I don't care but some
might:-) If you want new SCTP implementations to include
this then adding the UPDATES may make sense.

- 3.2, step 9: Just wondering: is this still true even if
the implementation knows that the ack was received from a
destination address that is currently in the PF state?
(Say if all destination addresses are on different
interfaces, and I can see on which interface I rx'd the
ack, and that maps 1:1 with a destination address in the PF
state.)

[Ballot comment]
- 3.2: Since PMR is allowed to be greater than zero, there is the potential to have a non-zero error count but not yet have entered the potentially failed state. Did I miss guidance on when the error count might be reset under those conditions? (I found guidance for when in the potentially failed state.)

-3.2, 4:
The paragraph says the sender MUST follow the following rules, but both of those rules just say SHOULD. I'm not sure what that means.

- 3.2, 7: "sender SHOULD clear the error counter"
Why not MUST?

- 4, 3rd paragraph: "handling SHOULD NOT
  be coupled"
Why not MUST?

- 6: The recommended value for PFMR is redundant with an earlier section.

Editorial:

- There are a number of places where paragraphs are put into long numbered lists for no apparent reason. Could those not just be normal paragraphs?  As it is, I keep getting section numbers and paragraph numbers confused.

- 3.2, 3.ii:"...the sender thus by [RFC4960], section 6.4.1, should attempt..."

The wording is confusion. I think you mean something to the effect of "According to [RFC4960] section 6.4.1, when the sender retransmits data that has timed out, it should attempt..."

- 3.2, 4, last paragraph:
The current wording can be interpreted ambiguously. I think you mean the following:
OLD
  The sender MUST NOT change the state and the error counter of
  any destination address regardless of whether it has been chosen
  for transmission or not.
NEW
  The sender MUST NOT change the state and the error counter of
  any destination address simply because it has been chosen for
  transmission.
END

- 6:
RECOMMENDATIONS should not be capitalized.

-7: The section says it's informational. Does that include child sections? I found at least one 2119 MAY at te end of 7.2.

[Ballot comment]
As discussed by Jürgen Schönwäder (part of this OPS DIR review) and the authors.

Jürgen: Since the I-D introduces the new state Potentially Failed, does this
  imply that an update of the SCTP-MIB [RFC3873] (sctpAssocState) is
  needed as well? Are there additional MIB objects to report, e.g.,
  spt_pathpfthld and spt_pathcpthld? I see some additional SCTP
  related docs in TSVWG and perhaps after they have been completed an
  update of the SCTP-MIB would make sense to consider.

Yoshifumi Nishida: I think it makes senses to update MIB. We'll check with implementors and other experts.
Thanks for pointing it out.

Ideally, you should add a sentence or two expressing that RFC3873 should be updated to support this functionality with a few objects that ...

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

IANA has reviewed draft-ietf-tsvwg-sctp-failover-14.txt, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any IANA 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, IANA does not 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: gorry@erg.abdn.ac.uk, tsvwg-chairs@ietf.org, tsvwg@ietf.org, spencerdawkins.ietf@gmail.com, draft-ietf-tsvwg-sctp-failover@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (SCTP-PF: Quick Failover Algorithm in SCTP) to Proposed Standard


The IESG has received a request from the Transport Area Working Group WG
(tsvwg) to consider the following document:
- 'SCTP-PF: Quick Failover Algorithm in SCTP'
  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 2015-12-23. 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


  SCTP supports multi-homing.  However, when the failover operation
  specified in RFC4960 is followed, there can be significant delay and
  performance degradation in the data transfer path failover.  To
  overcome this problem this document specifies a quick failover
  algorithm (SCTP-PF) based on the introduction of a Potentially Failed
  (PF) state in SCTP Path Management.

  The document also specifies a dormant state operation of SCTP.  This
  dormant state operation is required to be followed by an SCTP-PF
  implementation, but it may equally well be applied by a standard
  RFC4960 SCTP implementation.

  Additionally, the document introduces an alternative switchback
  operation mode called Primary Path Switchover that will be beneficial
  in certain situations.  This mode of operation applies to both a
  standard RFC4960 SCTP implementation as well as to a SCTP-PF
  implementation.

  The procedures defined in the document require only minimal
  modifications to the RFC4960 specification.  The procedures are
  sender-side only and do not impact the SCTP receiver.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover/ballot/


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

The following Last Call announcement was sent out:

From: The IESG
To: "IETF-Announce"
CC: gorry@erg.abdn.ac.uk, tsvwg-chairs@ietf.org, tsvwg@ietf.org, spencerdawkins.ietf@gmail.com, draft-ietf-tsvwg-sctp-failover@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (SCTP-PF: Quick Failover Algorithm in SCTP) to Proposed Standard


The IESG has received a request from the Transport Area Working Group WG
(tsvwg) to consider the following document:
- 'SCTP-PF: Quick Failover Algorithm in SCTP'
  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 2015-12-23. 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


  SCTP supports multi-homing.  However, when the failover operation
  specified in RFC4960 is followed, there can be significant delay and
  performance degradation in the data transfer path failover.  To
  overcome this problem this document specifies a quick failover
  algorithm (SCTP-PF) based on the introduction of a Potentially Failed
  (PF) state in SCTP Path Management.

  The document also specifies a dormant state operation of SCTP.  This
  dormant state operation is required to be followed by an SCTP-PF
  implementation, but it may equally well be applied by a standard
  RFC4960 SCTP implementation.

  Additionally, the document introduces an alternative switchback
  operation mode called Primary Path Switchover that will be beneficial
  in certain situations.  This mode of operation applies to both a
  standard RFC4960 SCTP implementation as well as to a SCTP-PF
  implementation.

  The procedures defined in the document require only minimal
  modifications to the RFC4960 specification.  The procedures are
  sender-side only and do not impact the SCTP receiver.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover/ballot/


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

draft-ietf-tsvwg-sctp-failover

As required by RFC4858, 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?

PS

(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:

This describes a standards-track procedure for SCTP to support of failover when working with a multi-homed SCTP end-point:

  SCTP supports multi-homing.  However, when the failover operation
  specified in RFC4960 is followed, there can be significant delay and
  performance degradation in the data transfer path failover.  To
  overcome this problem this document specifies a quick failover
  algorithm (SCTP-PF) based on the introduction of a Potentially Failed
  (PF) state in SCTP Path Management.

  The document also specifies a dormant state operation of SCTP.  This
  dormant state operation is required to be followed by an SCTP-PF
  implementation, but it may equally well be applied by a standard
  RFC4960 SCTP implementation.

  Additionally, the document introduces an alternative switchback
  operation mode called Primary Path Switchover that will be beneficial
  in certain situations.  This mode of operation applies to both a
  standard RFC4960 SCTP implementation as well as to a SCTP-PF
  implementation.

  The procedures defined in the document require only minimal
  modifications to the RFC4960 specification.  The procedures are
  sender-side only and do not impact the SCTP receiver.


Working Group Summary:


Document Quality:
The document is thought ready to publish.

Personnel:

Who is the Document Shepherd?
G Fairhurst (TSVWG Co-Chair)

Who is the Responsible Area Director?
Spencer Dawkins (TSV AD)


(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.

I have reviewed this document a number of times, and the requested improvements in quality and readability have been incorporated. I am happy the final document is ready to publish.

The feature specified by this document is implemented by multiple SCTP SW implementations and furthermore that various variants of the solution have been deployed in Telco signaling environments for several years with good results.

PF has been coded into FreeBSD, and plans to update to this spec.
Ericsson SW (supported in various forms for 5 years)
This feature is supported in Ericsson in-house SCTP SW implementation, and available for use in other stacks.

It is partially implemented in Linux SCTP SW (July 2014) with the intent to implement.

(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.

No.

(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?

OK - Yoshifumi Nishida
OK - Preethi Natarajan
OK - Armando Caro
OK - P. Amer
OK - K. Nielsen

(OK means the authors have confirmed that they comply withe provisions).

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

None known.

(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 document received support from TSVWG.

This document has received appropriate review by the TSV WG: The document was adopted by WG 26/6/2012. It has been reviewed by principal SCTP maintainers. A WGLC concluded 19th November, 2014 and was followed by significant work to improve the quality of the document and specification of the protocol. At the end of this updates  the authors worked with people raising comments to confirm the set of changes and a final 2 week WGLC in Sept 2015 confirmed acceptance of the final document by the TSVWG.

(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.

None

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

None

(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?

OK

(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

It was considered whether this updates the SCTP base specification RFC, but after consideration by the WG it was concluded this is an optional extension that should not update this spec. This seems in line with the update policy for SCTP 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).

This document requires no actions from 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.

None