Serving Stale Data to Improve DNS Resiliency
draft-ietf-dnsop-serve-stale-10

[Ballot comment]
Thanks for this document; it's some good comprehensive discussion of the
issues related to this topic and will improve the stability of the
internet.  I have several minor coments and a few side notes that
are expected to lead to at most my own elucidiation (but no textual
changes).

Section 2

  For a comprehensive treatment of DNS terms, please see [RFC8499].

(side note: I myself would not use the word "comprehensive" when it
explicitly says that "some DNS-related terms are interpreted quite
differently by different DNS experts", but I understand why it is used
here.)

Section 3

  There are a number of reasons why an authoritative server may become
  unreachable, including Denial of Service (DoS) attacks, network
  issues, and so on.  If a recursive server is unable to contact the
  authoritative servers for a query but still has relevant data that

side note: the way this is worded might make a reader wonder if the
recursive is expected to attempt to contact all known authoritatives
before declaring failure.

  Several recursive resolver operators, including Akamai, currently use
  stale data for answers in some way.  A number of recursive resolver

I did not follow the discussions that led to this wording, but one of my
colleagues at Akamai suggested that "currently fall back to stale data
for answers under some circumstances" might be a nicer wording, though I
note that Adam has already proposed some text here as well, which is
probably fine.

Section 4

  The definition of TTL in [RFC1035] Sections 3.2.1 and 4.1.3 is
  amended to read:

  TTL  a 32-bit unsigned integer number of seconds that specifies the
      duration that the resource record MAY be cached before the source
      of the information MUST again be consulted.  Zero values are
      interpreted to mean that the RR can only be used for the
      transaction in progress, and should not be cached.  Values SHOULD
      be capped on the orders of days to weeks, with a recommended cap
      of 604,800 seconds (seven days).  If the data is unable to be
      authoritatively refreshed when the TTL expires, the record MAY be
      used as though it is unexpired.  See the Section 5 and Section 6
      sections for details.

I recommend using "[this document]" in the section references, since a
reader reading the updated content in the context of RFC 1035 might look
there instead of here.

Section 5

  The resolver then checks its cache for any unexpired records that
  satisfy the request and returns them if available.  If it finds no
  relevant unexpired data and the Recursion Desired flag is not set in
  the request, it should immediately return the response without
  consulting the cache for expired records.  Typically this response
  would be a referral to authoritative nameservers covering the zone,
  but the specifics are implementation-dependent.

side note: I'm slightly surprised that the semantics of the absence of
Recusion Desired are not more tightly nailed down, but neither is it the
role of this document to specify them.

  When no authorities are able to be reached during a resolution
  attempt, the resolver should attempt to refresh the delegation and
  restart the iterative lookup process with the remaining time on the
  query resolution timer.  This resumption should be done only once
  during one resolution effort.

Is the "during one" more like a global cap or more like "during a
given"?

Section 6

  The client response timer is another variable which deserves
  consideration.  If this value is too short, there exists the risk
  that stale answers may be used even when the authoritative server is
  actually reachable but slow; this may result in sub-optimal answers
  being returned.  Conversely, waiting too long will negatively impact
  user experience.

Not just sub-optimal but potentially even wrong or actively harmful
answers, no?

  The balance for the failure recheck timer is responsiveness in
  detecting the renewed availability of authorities versus the extra
  resource use for resolution.  If this variable is set too large,
  stale answers may continue to be returned even after the
  authoritative server is reachable; per [RFC2308], Section 7, this
  should be no more than five minutes.  If this variable is too small,
  authoritative servers may be rapidly hit with a significant amount of
  traffic when they become reachable again.

I think part of the concern is also that setting the value too small
will cause additional traffic towards the authoritative even while it is
nonresponsive/nonreachable, which could aggravate any DoS attack ongoing
against the authoritative.  Which is to say, that perhaps "became
reachable again" does not quite reflect the full set of considerations.

  Regarding the TTL to set on stale records in the response,
  historically TTLs of zero seconds have been problematic for some
  implementations, and negative values can't effectively be
  communicated to existing software.  Other very short TTLs could lead
  to congestive collapse as TTL-respecting clients rapidly try to
  refresh.  The recommended value of 30 seconds not only sidesteps
  those potential problems with no practical negative consequences, it
  also rate limits further queries from any client that honors the TTL,
  such as a forwarding resolver.

I a little-bit wonder whether an RFC 8085 reference would make sense
here, but that's not exactly my area of expertise.

  There's also no record of TTLs in the wild having the most
  significant bit set in DNS-OARC's "Day in the Life" samples.  With no

Should we have a reference for DNS-OARC's samples?

  apparent reason for operators to use them intentionally, that leaves
  either errors or non-standard experiments as explanations as to why
  such TTLs might be encountered, with neither providing an obviously
  compelling reason as to why having the leading bit set should be
  treated differently from having any of the next eleven bits set and
  then capped per Section 4.

side note(?): This discussion, as roughly "we can't think of any reason
why the change would be problematic", calls to mind the ongoing
discussions of RFC (text) format changes, where arguments are being made
for more-strict backwards/historical compatibility.  That said, I have
no reason to doubt the WG consensus position here, hence "side note".

Section 7

  Be aware that Canonical Name (CNAME) and DNAME [RFC6672] records
  mingled in the expired cache with other records at the same owner
  name can cause surprising results.  This was observed with an initial
  implementation in BIND when a hostname changed from having an IPv4
  Address (A) record to a CNAME.  The version of BIND being used did
  not evict other types in the cache when a CNAME was received, which
  in normal operations is not a significant issue.  However, after both
  records expired and the authorities became unavailable, the fallback
  to stale answers returned the older A instead of the newer CNAME.

I'm not sure to what extent the lesson from this scenario is limited to
"CNAME/DNAME are special" versus "when serving stale, serve the
least-stale you have".

Section 8

  Details of Apple's implementation are not currently known.

I'm amenable to the other reviewer's comment that this section might be
interesting to keep, RFC 6982 notwithstanding, in which case this might
be more appropriately worded as "publicly disclosed" -- one assumes that
the Apple employees that wrote it know what it does!

Section 10

  The most obvious security issue is the increased likelihood of DNSSEC
  validation failures when using stale data because signatures could be
  returned outside their validity period.  Stale negative records can

We seem to be carefully not giving explicit guidance about using "stale"
DNSSEC keys in addition to stale resolution records.  If the
consequences of potentially using expired key material are more severe
than the consequences of potentially using expired DNS records (as it
seems to me), perhaps we should explicitly reiterate that serve-stale is
not an excuse to ignore key validity periods (as we are implicitly doing
here)?

  In [CloudStrife], it was demonstrated how stale DNS data, namely
  hostnames pointing to addresses that are no longer in use by the
  owner of the name, can be used to co-opt security such as to get
  domain-validated certificates fraudulently issued to an attacker.
  While this document does not create a new vulnerability in this area,
  it does potentially enlarge the window in which such an attack could
  be made.  A proposed mitigation is that certificate authorities
  should fully look up each name starting at the DNS root for every
  name lookup.  Alternatively, CAs should use a resolver that is not
  serving stale data.

[I think Adam has probably already covered this one, but keeping just in
case.]
I note that the target of this guidance (CAs) is not obviously in the
expected readership set for a document about DNS recursive resolver
operational considerations.  Can we do more to expand the visibility of
this guidance to the audience where it would be most useful?  (I don't
see an obvious candidate for, e.g., an additional Updates: relationship,
but perhaps someone has other ideas.)

[Ballot comment]
* Section 6

It might be useful to include a reference to DITL for some background on the dataset mentioned in this section

http://www.caida.org/projects/ditl/

[Ballot comment]
* I agree with Mirja, Section 8 is more informative than what is alluded to the paragraph starting with “Several recursive resolvers …” in Section 3, and IMO is worth keeping.  I struck me as odd to call out the operation practice of a particular vendor (Akamai).  We might want to check if this reference is ok – Ben?

* A few reference nits:
- Section 6.  Per the mention to DNS-OARC, please provide a citation.
- Section 6 and 9.  The text references “during discussions in the IETF”.  What is that specifically – WG deliberation?

* Thanks for covering the attacker use cases of stale data in Section 10.

[Ballot comment]
* I agree with Mirja, Section 8 is more informative than what is alluded to the paragraph starting with “Several recursive resolvers …” in Section 3, and IMO is worth keeping.  I struck me as odd to call out the operation practice of a particular vendor (Akamai).  We might want to check if this reference is ok – Ben?

* A few reference nits:
- Section 6.  Per the mention to DNS-OARC, please provide a citation.
- Section 6 and 9.  The text references “during discussions in the IETF”.  What is that specifically – WG deliberation?

* Thanks for covering how the attacker use cases of stale data in Section 10.

[Ballot comment]

Thanks to everyone who put work into documenting this useful and apparently
well-deployed mechanism. I have a handful of comments on the current document.

---------------------------------------------------------------------------

§3:

>  Several recursive resolver operators, including Akamai, currently use
>  stale data for answers in some way.

This won't age well; and it's not clear why calling out Akamai amongst
the various DNS service providers is warranted. Suggest:

  At the time of this document's publication, several recursive resolver
  operators use stale data for answers in some way

(If the notion of citing Akamai is to indicate the scale of such operators,
I suggest "...operators, including large-scale operators, use stale...")

---------------------------------------------------------------------------

§4:

>  The definition of TTL in [RFC1035] Sections 3.2.1 and 4.1.3 is
>  amended to read:
>
>  TTL  a 32-bit unsigned integer number of seconds that specifies the
>    duration that the resource record MAY be cached before the source
>    of the information MUST again be consulted.  Zero values are
>    interpreted to mean that the RR can only be used for the
>    transaction in progress, and should not be cached.  Values SHOULD
>    be capped on the orders of days to weeks, with a recommended cap
>    of 604,800 seconds (seven days).  If the data is unable to be
>    authoritatively refreshed when the TTL expires, the record MAY be
>    used as though it is unexpired.  See the Section 5 and Section 6
>    sections for details.


The addition of what I must presume is intended to be RFC 2119 language to a
document that doesn't cite RFC 2119 seems questionable.  I would suggest
either explicitly adding RFC 2119 boilerplate to RFC 1035 as part of this
update, or using plain English language to convey the same concepts as are
intended.

Nit: "See the Section 5 and Section 6 sections for details" is a very awkward
way to phrase the closing sentence.

More substantively: Sections 5 and 6 of RFC 1035 are "MASTER FILES" and "NAME
SERVER IMPLEMENTATION" respectively. Is this final sentence intended to refer to
those two sections? Or is it pointing to "Example Method" and "Implementation
Considerations" of this document? If the latter, please specifically cite this
document (e.g., "See Section 5 and Section 6 of [RFCXXXX] for details.")

---------------------------------------------------------------------------

§4:

>  therefor leave any previous state intact.  See Section 6 for a

Nit: "therefore"

---------------------------------------------------------------------------

§5:

>  When a request is received by a recursive resolver, it should start
>  the client response timer.

The passive tense in this sentence makes "it" linguistically ambiguous.
Suggest: "When the recursive resolver receives a request, it should start..."

---------------------------------------------------------------------------

§10:

>  A proposed mitigation is that certificate authorities
>  should fully look up each name starting at the DNS root for every
>  name lookup.  Alternatively, CAs should use a resolver that is not
>  serving stale data.

This seems like a perfectly good solution, although I wonder how many CAs are
likely to read this document. If I were the type to engage in wagering, I'd
put all of my money on "zero." I'm not sure specific action is called for
prior to publication of this document as an RFC, but it seems that additional
publicity of this issue and the way that serve-stale interacts with it --
e.g., to CAB Forum and its members -- is warranted.

[Ballot comment]
Two comments:

1) It seems to me that this sentence in section 7 should/could actually be phrased as a normative requirement in this document:
"it is not necessary that every client request needs to
  trigger a new lookup flow in the presence of stale data, but rather
  that a good-faith effort has been recently made to refresh the stale
  data before it is delivered to any client."
Maybe worth considering...

2) I find the Implementation Status section (8) actually quite interesting for this document and maybe it should be considered to keep it in the document for final publication.

[Ballot comment]
Thank you for the work put into this document. The short document is easy to read. Feel free to ignore the sentences below.

I loved the sentence "stale bread is better than no bread.", who said that I-D are boring? :-)

Should the assertion about DNS stale data by products (end of section 3) be documented by external documents? Somehow addressed in section 8 (to be removed...)

Finally, I am unsure whether it is worth documenting the WG discussion about EDNS.

Regards,

-éric

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

The IANA Functions Operator has reviewed draft-ietf-dnsop-serve-stale-07, 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 2019-09-25):

From: The IESG
To: IETF-Announce
CC: dnsop-chairs@ietf.org, draft-ietf-dnsop-serve-stale@ietf.org, dnsop@ietf.org, suzworldwide@gmail.com, Suzanne Woolf , barryleiba@gmail.com
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Serving Stale Data to Improve DNS Resiliency) to Proposed Standard


The IESG has received a request from the Domain Name System Operations WG
(dnsop) to consider the following document: - 'Serving Stale Data to Improve
DNS Resiliency'
  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 2019-09-25. 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 draft defines a method (serve-stale) for recursive resolvers to
  use stale DNS data to avoid outages when authoritative nameservers
  cannot be reached to refresh expired data.  One of the motivations
  for serve-stale is to make the DNS more resilient to DoS attacks, and
  thereby make them less attractive as an attack vector.  This document
  updates the definitions of TTL from RFC 1034 and RFC 1035 so that
  data can be kept in the cache beyond the TTL expiry, and also updates
  RFC 2181 by interpreting values with the high order bit set as being
  positive, rather than 0, and also suggests a cap of 7 days.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-dnsop-serve-stale/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-dnsop-serve-stale/ballot/

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

  https://datatracker.ietf.org/ipr/3589/
  https://datatracker.ietf.org/ipr/3014/
  https://datatracker.ietf.org/ipr/3590/
  https://datatracker.ietf.org/ipr/3059/
  https://datatracker.ietf.org/ipr/3573/
  https://datatracker.ietf.org/ipr/2967/
  https://datatracker.ietf.org/ipr/2968/

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?

Proposed standard. It updates the definition of TTL in RFC 1034, 1035, and 2181.

(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 draft defines a method (serve-stale) for recursive resolvers to
  use stale DNS data to avoid outages when authoritative nameservers
  cannot be reached to refresh expired data.  It updates the definition
  of TTL from RFCs 1034, 1035, and 2181 to make it clear that
  data can be kept in the cache beyond the TTL expiry and used for
  responses when a refreshed answer is not readily available. (From the Abstract.)

Working Group Summary

  This draft dates to March 2017 and was adopted by DNSOP in October 2017. It's been extensively reviewed in the WG. The primary point of controversy was that it discusses an optional protocol change (the choice by a recursive resolver to re-use data beyond the authoritative server TTL when no refresh is available) that some WG participants felt to be unwise under some conditions. The discussion of timer values in Sec. 5, and of implementation decisions and caveats in Sec. 6 and Sec. 7, seem to address these concerns. Since this protocol modification is widely implemented and deployed, having a standards track description seemed to promote careful practice and interoperability.

Document Quality

  The protocol update discussed in this draft is an attempt to document behavior that is implemented in multiple open source DNS codebases and deployed by a number of large operators, including DNS services and CDNs that rely on the specified DNS behavior. Common practice regarding the handling of TTLs by recursive resolvers has changed considerably over the behavior originally specified, and documenting the current practice as an update to the protocol seems likely to promote interoperability and transparency under both normal and adverse conditions.

Personnel

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

Suzanne Woolf (shepherd)
Barry Leiba (AD; the WG's AD, Warren Kumari, is an author.)

(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.

There are some minor issues (typos, minor copyedits) but this document is ready for IESG review. (-07)

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No. The WG core of participants are exactly the people to review this, based on protocol knowledge, implementation experience, and operational experience.

(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.

From time to time, DNSOP considers documents that describe DNS behavior that might be controversial, or whose costs and benefits are not universally agreed on. In those situations, sometimes the WG has to decide whether they feel that the documented behavior is harmful, and if so whether documenting it encourages or limits the harm. Some discussion along those lines occurred around this document. The chairs believe the concerns were addressed and there is consensus to advance the document.

(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.

All authors have confirmed.

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

There are several IPR disclosures. In all three cases of specific disclosures, the companies responsible have affirmed they're granting licenses for any use of their technology in the implementation of this draft.


(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? 

This document seems to be supported by multiple implementers and operators as reflecting current or planned practice, with the benefits and caveats described.

(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.


There are a number of update_references warnings from idnits. Some are hard to parse (they flag external references e.g. [DikeBreaks]). Many are due to the extensive discussion of changes in meaning of terms now considered RFC2119-normative as used in a much older RFC (1034). The warning about an improper URL is spurious (it's a live URL, not an example, and it's in an "Implementation Experience" section that will be removed prior to publication.)

(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.

This document updates RFCs 1034, 1035, and 2181. The shepherd believes the intended effect is clear.


(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 8126).

There are no actions for IANA in this document, and it has no impact on the meaning of any existing IANA registry or allocated codepoint. It updates the use of a field in DNS RRs as defined in the original specification but requires no change to that definition.


(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

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?

Proposed standard. It updates the definition of TTL in RFC 1034, 1035, and 2181.

(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 draft defines a method (serve-stale) for recursive resolvers to
  use stale DNS data to avoid outages when authoritative nameservers
  cannot be reached to refresh expired data.  It updates the definition
  of TTL from RFCs 1034, 1035, and 2181 to make it clear that
  data can be kept in the cache beyond the TTL expiry and used for
  responses when a refreshed answer is not readily available. (From the Abstract.)

Working Group Summary

  This draft dates to March 2017 and was adopted by DNSOP in October 2017. It's been extensively reviewed in the WG. The primary point of controversy was that it discusses an optional protocol change (the choice by a recursive resolver to re-use data beyond the authoritative server TTL when no refresh is available) that some WG participants felt to be unwise under some conditions. The discussion of timer values in Sec. 5, and of implementation decisions and caveats in Sec. 6 and Sec. 7, seem to address these concerns. Since this protocol modification is widely implemented and deployed, having a standards track description seemed to promote careful practice and interoperability.

Document Quality

  The protocol update discussed in this draft is an attempt to document behavior that is implemented in multiple open source DNS codebases and deployed by a number of large operators, including DNS services and CDNs that rely on the specified DNS behavior. Common practice regarding the handling of TTLs by recursive resolvers has changed considerably over the behavior originally specified, and documenting the current practice as an update to the protocol seems likely to promote interoperability and transparency under both normal and adverse conditions.

Personnel

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

Suzanne Woolf (shepherd)
Barry Leiba (AD; the WG's AD, Warren Kumari, is an author.)

(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.

There are some minor issues (typos, minor copyedits) but this document is ready for IESG review. (-07)

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No. The WG core of participants are exactly the people to review this, based on protocol knowledge, implementation experience, and operational experience.

(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.

From time to time, DNSOP considers documents that describe DNS behavior that might be controversial, or whose costs and benefits are not universally agreed on. In those situations, sometimes the WG has to decide whether they feel that the documented behavior is harmful, and if so whether documenting it encourages or limits the harm. Some discussion along those lines occurred around this document. The chairs believe the concerns were addressed and there is consensus to advance the document.

(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.

All authors have confirmed.

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

There are several IPR disclosures. In all three cases of specific disclosures, the companies responsible have affirmed they're granting licenses for any use of their technology in the implementation of this draft.


(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? 

This document seems to be supported by multiple implementers and operators as reflecting current or planned practice, with the benefits and caveats described.

(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.


There are a number of update_references warnings from idnits. Some are hard to parse (they flag external references e.g. [DikeBreaks]). Many are due to the extensive discussion of changes in meaning of terms now considered RFC2119-normative as used in a much older RFC (1034). The warning about an improper URL is spurious (it's a live URL, not an example, and it's in an "Implementation Experience" section that will be removed prior to publication.)

(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.

This document updates RFCs 1034, 1035, and 2181. The shepherd believes the intended effect is clear.


(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 8126).

There are no actions for IANA in this document, and it has no impact on the meaning of any existing IANA registry or allocated codepoint. It updates the use of a field in DNS RRs as defined in the original specification but requires no change to that definition.


(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

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?

Proposed standard. It updates the definition of TTL in RFC 1034, 1035, and 2181.

(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 draft defines a method (serve-stale) for recursive resolvers to
  use stale DNS data to avoid outages when authoritative nameservers
  cannot be reached to refresh expired data.  It updates the definition
  of TTL from [RFC1034], [RFC1035], and [RFC2181] to make it clear that
  data can be kept in the cache beyond the TTL expiry and used for
  responses when a refreshed answer is not readily available. (From the Abstract.)

Working Group Summary

  This draft dates to March 2017 and was adopted by DNSOP in October 2017. It's been extensively reviewed in the WG. The primary point of controversy was that it discusses an optional protocol change (the choice by a recursive resolver to re-use data beyond the authoritative server TTL when no refresh is available) that some WG participants felt to be unwise under some conditions. The discussion of timer values in Sec. 5, and of implementation decisions and caveats in Sec. 6 and Sec. 7, seem to address these concerns. Since this protocol modification is widely implemented and deployed, having a standards track description seemed to promote careful practice and interoperability.

Document Quality

  The protocol update discussed in this draft is an attempt to document behavior that is implemented in multiple open source DNS codebases and deployed by a number of large operators, including DNS services and CDNs that rely on the specified DNS behavior. Common practice regarding the handling of TTLs by recursive resolvers has changed considerably over the behavior originally specified, and documenting the current practice as an update to the protocol seems likely to promote interoperability and transparency under both normal and adverse conditions.

Personnel

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

Suzanne Woolf (shepherd)
Barry Leiba (AD; the WG's AD, Warren Kumari, is an author.)

(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.

There are some minor issues (typos, minor copyedits) but this document is ready for IESG review. (-07)

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No. The WG core of participants are exactly the people to review this, based on protocol knowledge, implementation experience, and operational experience.

(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.

From time to time, DNSOP considers documents that describe DNS behavior that might be controversial, or whose costs and benefits are not universally agreed on. In those situations, sometimes the WG has to decide whether they feel that the documented behavior is harmful, and if so whether documenting it encourages or limits the harm. Some discussion along those lines occurred around this document. The chairs believe the concerns were addressed and there is consensus to advance the document.

(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.

(*** waiting for confirmation)

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

There are several IPR disclosures. In all three cases of specific disclosures, the companies responsible have affirmed they're granting licenses for any use of their technology in the implementation of this draft.


(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? 

This document seems to be supported by multiple implementers and operators as reflecting current or planned practice, with the benefits and caveats described.

(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.


There are a number of update_references warnings from idnits. Some are hard to parse (they flag external references e.g. [DikeBreaks]). Many are due to the extensive discussion of changes in meaning of terms now considered RFC2119-normative as used in a much older RFC (1034). The warning about an improper URL is spurious (it's a live URL, not an example, and it's in an "Implementation Experience" section that will be removed prior to publication.)

(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.

This document updates RFC1034, 1035, and 2181. The shepherd believes the intended effect is clear.


(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 8126).

There are no actions for IANA in this document, and it has no impact on the meaning of any existing IANA registry or allocated codepoint.


(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

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?

Proposed standard. It updates the definition of TTL in RFC 1034 and 1035. (*** This needs to be fixed for -07.)

(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:

(*** authors please review)

Technical Summary

  This draft defines a method (serve-stale) for recursive resolvers to
  use stale DNS data to avoid outages when authoritative nameservers
  cannot be reached to refresh expired data.  It updates the definition
  of TTL from [RFC1034], [RFC1035], and [RFC2181] to make it clear that
  data can be kept in the cache beyond the TTL expiry and used for
  responses when a refreshed answer is not readily available. (From the Abstract.)

Working Group Summary

  This draft dates to March 2017 and was adopted by DNSOP in October 2017. It's been extensively reviewed in the WG. The primary point of controversy was that it discusses an optional protocol change (the choice by a recursive resolver to re-use data beyond the authoritative server TTL when no refresh is available) that some WG participants felt to be unwise under some conditions. The discussion of timer values in Sec. 5, and of implementation decisions and caveats in Sec. 6 and Sec. 7, seem to address these concerns. Since this protocol modification is widely implemented and deployed, having a standards track description seemed to promote careful practice and interoperability.

Document Quality

  The protocol update discussed in this draft is an attempt to document behavior that is implemented in multiple open source DNS codebases and deployed by a number of large operators, including DNS services and CDNs that rely on the specified DNS behavior. Common practice regarding the handling of TTLs by recursive resolvers has changed considerably over the behavior originally specified, and documenting the current practice as an update to the protocol seems likely to promote interoperability and transparency under both normal and adverse conditions.

Personnel

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

Suzanne Woolf (shepherd)
Ignas Bagdonas (AD; the WG's AD, Warren Kumari, is an author.)

(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.

There are some minor issues (typos, a reference that needs to be updated) but this document is ready for IESG review. (-06)

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No. The WG core of participants are exactly the people to review this, based on protocol knowledge, implementation experience, and operational experience.

(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.

From time to time, DNSOP considers documents that describe DNS behavior that might be controversial, or whose costs and benefits are not universally agreed on. In those situations, sometimes the WG has to decide whether they feel that the documented behavior is harmful, and if so whether documenting it encourages or limits the harm. Some discussion along those lines occurred around this document. The chairs believe the concerns were addressed and there is consensus to advance the document.

(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.

(*** waiting for confirmation)

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

There are several IPR disclosures. In all three cases of specific disclosures, the companies responsible have affirmed they're granting licenses for any use of their technology in the implementation of this draft.


(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? 

This document seems to be supported by multiple implementers and operators as reflecting current or planned practice, with the benefits and caveats described.

(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.

(*** authors please run idnits in "very verbose" mode and review-- there are a couple of places where bracketed reference format is used where I believe the unbracketed form is considered correct, but I think most of the update_references warnings are from using RFC 2119 terms in-line, in their non-normative sense.)

There are a number of update_references warnings from idnits. A couple are substantive (RFC 7199 was obsoleted by RFC 8499), a couple are harder to parse (they flag external references e.g. [DikeBreaks]). Many are due to the extensive discussion of changes in meaning of terms now considered RFC2119-normative as used in a much older RFC (1034). The warning about an improper URL is spurious (it's a live URL, not an example, and it's in an "Implementation Experience" section that will be removed prior to publication.)

(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.

This document updates RFC1034 and RFC 1035. The shepherd believes the intended effect is clear.

(*** Authors may wish to edit so that all updated RFCs are explicitly discussed in the Introduction.)


(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 8126).

There are no actions for IANA in this document, and it has no impact on the meaning of any existing IANA registry or allocated codepoint.


(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