Default Address Selection for Internet Protocol Version 6 (IPv6)
RFC 6724

Received changes through RFC Editor sync (changed abstract to 'This document describes two algorithms, one for source address selection and one for destination address selection. The algorithms specify default behavior for all Internet Protocol version 6 (IPv6) implementations. They do not override choices made by applications or upper-layer protocols, nor do they preclude the development of more advanced mechanisms for address selection. The two algorithms share a common context, including an optional mechanism for allowing administrators to provide policy that can override the default behavior. In dual-stack implementations, the destination address selection algorithm can consider both IPv4 and IPv6 addresses -- depending on the available source addresses, the algorithm might prefer IPv6 addresses over IPv4 addresses, or vice versa.

Default address selection as defined in this specification applies to all IPv6 nodes, including both hosts and routers. This document obsoletes RFC 3484. [STANDARDS-TRACK]')

[Ballot comment]

These comments are provided with the goal of improving the readability
and completeness of the information in the document.  I apologize for
the vagueness of my complaints about readability in comment 4; if
everyone else is able to read and understand the text I commented on,
feel free to ignore my suggestions.

1. I suggest adding a sentence explaining the status of IPv6
site-local unicast addresses and why they are included in the
procedures in this document.  Perhaps something like:

  "IPv6 site-local unicast addresses are deprecated [RFC 4291].
  However, some existing implementations and deployments may still
  use these addresses and, therefore, they are included in the
  procedures in this specification."

2. There is a minor conflict between the definitions of IPv6 multicast
scopes in RFC 4007 and RFC 4291.  I couldn't find an errata about the
issue.  RFC 4291 lists scope field value 0x03 as "undefined".  The
information kept by IANA seems to show RFC 4291 for multicast issues
in
www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xml,
so, for consistency, this document might want to follow RFC 4291.

3. Minor editorial suggestion in section 4:

OLD:

  It is RECOMMENDED that the candidate source addresses be the set of
  unicast addresses assigned to the interface that will be used to send
  to the destination.  (The "outgoing" interface.)

NEW:

  It is RECOMMENDED that the candidate source addresses be the set of
  unicast addresses assigned to the interface that will be used to send
  to the destination (the "outgoing" interface).

4. The one part of this otherwise excellent document I find confusing
is the candidate source address selection procedure in section 4.  It
took several readings for me to understand how the rules in that
section are applied; e.g., which rules modify, override or are
considered in parallel with other rules.  I was unable to understand
this paragraph (which seems like it should be swapped with the
paragraph immediately following it for clarity):

  If an application or upper layer specifies a source address that is
  not in the candidate set for the destination, then the network layer
  MUST treat this as an error.  The specified source address may
  influence the candidate set, by affecting the choice of outgoing
  interface.

However, I'm not sure I have any good suggestions for broad
improvement.  Here are a few small suggestions:

  For all multicast and link-local unicast destination addresses...

  For site-local unicast addresses...

  Perhaps move the paragraph that begins "It is RECOMMENDED..." to
  the end of section 4 and begin it with "Unless otherwise specified
  above, it is RECOMMENDED..."

5. In section 5, the text describing the comparison rules specifies
three outcomes for each rule, "greater than," "less than" or "equal
to," while none of the rules explicitly defines an "equal to" outcome.
For completeness, I suggest adding a sentence explicitly identifying
the default result for each rule is "equal to".

6. Section 5, Rule 3: s/The addresses/If the addresses/

[Ballot discuss]

  Please consider the security considerations question raised in the
  Gen-ART Review by Ben Campbell on 14-Jun-2012.  I think this question
  deserves a response.  The Gen-ART Review can be found here:
  http://www.ietf.org/mail-archive/web/gen-art/current/msg07513.html

[Ballot comment]

- Source address rule 5.5 has a lowercase "shall" - since it looks like
this document has had a fairly careful scrubbing of lowercase 2119
language I wondered if that's really a 2119 MUST or a "can"?

- Destination address rule 7 discussion: maybe s/6RD/6rd/ ?

[Ballot comment]
Thank you for a comprehensive Appendix B that made reviewing this
document much easier.

---

I note that the Ballot Write-up includes text from an old version of
the Abstract saying:

  All IPv6 nodes, including both hosts and routers, must implement
  default address selection as defined in this specification.

This strong requirement appears to have been relaxed in the final
revision. Please update the ballot.

IANA has reviewed draft-ietf-6man-rfc3484bis-05, which is currently in Last Call, and has the following comments:

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

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Subject: Last Call:  (Default Address Selection for Internet Protocol version 6 (IPv6)) to Proposed Standard


The IESG has received a request from the IPv6 Maintenance WG (6man) to
consider the following document:
- 'Default Address Selection for Internet Protocol version 6 (IPv6)'
  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 2012-06-15. 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


  This document describes two algorithms, one for source address
  selection and one for destination address selection.  The algorithms
  specify default behavior for all Internet Protocol version 6 (IPv6)
  implementations.  They do not override choices made by applications
  or upper-layer protocols, nor do they preclude the development of
  more advanced mechanisms for address selection.  The two algorithms
  share a common context, including an optional mechanism for allowing
  administrators to provide policy that can override the default
  behavior.  In dual stack implementations, the destination address
  selection algorithm can consider both IPv4 and IPv6 addresses -
  depending on the available source addresses, the algorithm might
  prefer IPv6 addresses over IPv4 addresses, or vice-versa.

  Default address selection as defined in this specification applies to
  all IPv6 nodes, including both hosts and routers.  This document
  obsoletes RFC 3484.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-6man-rfc3484bis/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-6man-rfc3484bis/ballot/


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

All,
    Here are my comments on the Address Selection draft.  I think it is in really good shape and only have a few comments/questions/suggestions.  Many of these are related to text directly inherited from RFC 3484, so I am willing to listen to push back on making those changes.

1. The first line of the Abstract does not read well.  I suggest changing it to "... two algorithms, one for source address selection and one for...".

2. There has been resistance to having normative text in the Abstract and the first sentence of the second paragraph certainly sounds normative.  Any objection to striking that first sentence?  Would it make sense to move that sentence to the last paragraph in the Introduction?

3. The fourth paragraph of section 2 says apps SHOULD iterate through the list of addresses returned from getaddrinfo().  It would be useful to identify what exceptions to that rule are reasonable.

4. Section 2.1 (6th paragraph) mentions ULAs and 6to4 without expansion or reference.  It would be good to spell out what those are.

5. I am curious as to what the rationale was for changing the text in section 2.2 as opposed to keeping the original text from RFC 3484.  In making that change, why is only the length of S's prefix listed as a stopping criteria for comparison?

6. In section 3.1, I find it confusing to discuss "unicast site-local" and not mention the scope of ULAs.  In fact, it may be worthwhile to mention in section 2.1 that the placement of FEC0::/10 is based on the site-local prefix having been deprecated.

7. Section 5 states "...the remaining rules are applied (in order) to ...".  I would like to see this rule strengthened with the use of MUST or SHOULD.  In addition, the last paragraph in the section may lead some implementers to consider some of the rules as optional.  Is that really what we want?

8. This comment is driven by text in Section 6, but there are other cases throughout the document.  In several places, I find "should" and "may" being used in situations where it could be normative.  Is the intent to interpret mixed- and lower-case 2119 keywords as normative?

9. Section 7 contains an indirect reference to a rule by using "Rule 5.5".  It would read better if it said something like "Rule 5 in Section 5" or something similar.

Once we resolve these, the draft can move along to IETF Last Call.

Regards,
Brian

Title          : Default Address Selection for Internet Protocol version 6 (IPv6)
Author(s)      : Dave Thaler
                  Richard Draves
                  Arifumi Matsumoto
                  Tim Chown
Filename        : draft-ietf-6man-rfc3484bis-04.txt
Pages          : 30
Date            : 2012-05-15


(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.  It Obsoletes RFC3484, an existing standards track document.
  The header indicates Standards Track.

(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 document describes two algorithms, for source address selection
  and for destination address selection.  The algorithms specify
  default behavior for all Internet Protocol version 6 (IPv6)
  implementations.  They do not override choices made by applications
  or upper-layer protocols, nor do they preclude the development of
  more advanced mechanisms for address selection.  The two algorithms
  share a common context, including an optional mechanism for allowing
  administrators to provide policy that can override the default
  behavior.  In dual stack implementations, the destination address
  selection algorithm can consider both IPv4 and IPv6 addresses -
  depending on the available source addresses, the algorithm might
  prefer IPv6 addresses over IPv4 addresses, or vice-versa.

  All IPv6 nodes, including both hosts and routers, must implement
  default address selection as defined in this specification.

Working Group Summary

  The working group has been working on this replacement to RFC3484 for several years.
  There has been a very active discussion and there is a strong consensus to move it forward.

Document Quality

  This document has been reviewed by many people and the chairs believe there is
  agreement in the w.g. to move it forward. 

Personnel

  Bob Hinden is the Document Shepherd.
  Brian Haberman is the Responsible Area Director.

(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.

  Read the document and checked for NITs.  It 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? 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.

  The document authors:

    Dave Thaler
    Richard Draves
    Arifumi Matsumoto
    Tim Chown

have said they complied with the IPR rules as defined in BCP 78 and BCP 79.


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

  I am not aware of any 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? 

  There is a strong consensus to move this forward.  The working groups
  thinks it solves an important problem and should replace RFC3484.

(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.

  idnits complained about several instances of IPv4 and IPv6 addresses
  that are not the "documentation addresses". 

  == There are 4 instances of lines with non-RFC5735-compliant IPv4 addresses
      in the document.  If these are example addresses, they should be changed.

  The above all intentionally use IPv4 link-scoped addresses, which is
  what they're showing the effect on in the examples.  There are no such
  addresses reserved for documentation purposes.

  == There are 9 instances of lines with private range IPv4 addresses in the
      document.  If these are generic example addresses, they should be changed
      to use any of the ranges defined in RFC 5735 (or successor): 192.0.2.x,
      198.51.100.x or 203.0.113.x.

  The above all intentionally use IPv4 private addresses, which is what they're
  showing the effect on in the examples.  There are no such addresses reserved
  for documentation purposes.

  == There are 5 instances of lines with non-RFC3849-compliant IPv6 addresses
      in the document.  If these are example addresses, they should be changed.

  The above intentionally uses the 6to4 prefix, but c633:6401 is an embedded IPv4
  address of 198.51.100.1 which is an RFC 5737 documentation address (TEST-NET-2).


(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 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.

  Yes, it obsoletes RFC3484 as shown in the header.


(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).

  There are no IANA actions defined in 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.

  N/A

(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