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Versions: (draft-wkumari-dnsop-extended-error) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 16

Network Working Group                                          W. Kumari
Internet-Draft                                                    Google
Intended status: Standards Track                                 E. Hunt
Expires: November 6, 2020                                            ISC
                                                               R. Arends
                                                                   ICANN
                                                             W. Hardaker
                                                                 USC/ISI
                                                             D. Lawrence
                                                            Oracle + Dyn
                                                            May 05, 2020


                          Extended DNS Errors
                   draft-ietf-dnsop-extended-error-16

Abstract

   This document defines an extensible method to return additional
   information about the cause of DNS errors.  Though created primarily
   to extend SERVFAIL to provide additional information about the cause
   of DNS and DNSSEC failures, the Extended DNS Errors option defined in
   this document allows all response types to contain extended error
   information.  Extended DNS Error information does not change the
   processing of RCODEs.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 6, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and background . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
   2.  Extended DNS Error EDNS0 option format  . . . . . . . . . . .   4
   3.  Extended DNS Error Processing . . . . . . . . . . . . . . . .   5
   4.  Defined Extended DNS Errors . . . . . . . . . . . . . . . . .   5
     4.1.  Extended DNS Error Code 0 - Other . . . . . . . . . . . .   6
     4.2.  Extended DNS Error Code 1 -
           Unsupported DNSKEY Algorithm  . . . . . . . . . . . . . .   6
     4.3.  Extended DNS Error Code 2 - Unsupported DS
           Digest Type . . . . . . . . . . . . . . . . . . . . . . .   6
     4.4.  Extended DNS Error Code 3 - Stale Answer  . . . . . . . .   6
     4.5.  Extended DNS Error Code 4 - Forged Answer . . . . . . . .   6
     4.6.  Extended DNS Error Code 5 - DNSSEC Indeterminate  . . . .   6
     4.7.  Extended DNS Error Code 6 - DNSSEC Bogus  . . . . . . . .   6
     4.8.  Extended DNS Error Code 7 - Signature Expired . . . . . .   6
     4.9.  Extended DNS Error Code 8 - Signature Not Yet Valid . . .   7
     4.10. Extended DNS Error Code 9 - DNSKEY Missing  . . . . . . .   7
     4.11. Extended DNS Error Code 10 - RRSIGs Missing . . . . . . .   7
     4.12. Extended DNS Error Code 11 - No Zone Key Bit Set  . . . .   7
     4.13. Extended DNS Error Code 12 - NSEC Missing . . . . . . . .   7
     4.14. Extended DNS Error Code 13 - Cached Error . . . . . . . .   7
     4.15. Extended DNS Error Code 14 - Not Ready  . . . . . . . . .   7
     4.16. Extended DNS Error Code 15 - Blocked  . . . . . . . . . .   7
     4.17. Extended DNS Error Code 16 - Censored . . . . . . . . . .   7
     4.18. Extended DNS Error Code 17 - Filtered . . . . . . . . . .   8
     4.19. Extended DNS Error Code 18 - Prohibited . . . . . . . . .   8
     4.20. Extended DNS Error Code 19 - Stale NXDOMAIN Answer  . . .   8
     4.21. Extended DNS Error Code 20 - Not Authoritative  . . . . .   8
     4.22. Extended DNS Error Code 21 - Not Supported  . . . . . . .   8
     4.23. Extended DNS Error Code 22 - No Reachable Authority . . .   8
     4.24. Extended DNS Error Code 23 - Network Error  . . . . . . .   8
     4.25. Extended DNS Error Code 24 - Invalid Data . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  A New Extended DNS Error Code EDNS Option . . . . . . . .   9
     5.2.  New Registry for Extended DNS Error Codes . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12



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   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction and background

   There are many reasons that a DNS query may fail, some of them
   transient, some permanent; some can be resolved by querying another
   server, some are likely best handled by stopping resolution.
   Unfortunately, the error signals that a DNS server can return are
   very limited, and are not very expressive.  This means that
   applications and resolvers often have to "guess" at what the issue is
   - e.g. was the answer marked REFUSED because of a lame delegation, or
   because the nameserver is still starting up and loading zones?  Is a
   SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing
   some other failure?  What error messages should be presented to the
   user or logged under these conditions?

   A good example of issues that would benefit from additional error
   information are errors caused by DNSSEC validation issues.  When a
   stub resolver queries a name which is DNSSEC bogus [RFC8499] (using a
   validating resolver), the stub resolver receives only a SERVFAIL in
   response.  Unfortunately, the SERVFAIL Response Code (RCODE) is used
   to signal many sorts of DNS errors, and so the stub resolver's only
   option is to ask the next configured DNS resolver.  The result of
   trying the next resolver is one of two outcomes: either the next
   resolver also validates, and a SERVFAIL is returned again, or the
   next resolver is not a validating resolver, and the user is returned
   a potentially harmful result.  With an Extended DNS Error (EDE)
   option enclosed in the response message, the resolver is able to
   return a more descriptive reason as to why any failures happened, or
   add additional context to a message containing a NOERROR RCODE.

   This document specifies a mechanism to extend DNS errors to provide
   additional information about the cause of an error.  These extended
   DNS error codes are described in this document can be used by any
   system that sends DNS queries and receives a response containing an
   EDE option.  Different codes are useful in different circumstances,
   and thus different systems (stub resolvers, recursive resolvers, and
   authoritative resolvers) might receive and use them.

1.1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP



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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Extended DNS Error EDNS0 option format

   This draft uses an EDNS0 ([RFC6891]) option to include Extended DNS
   Error (EDE) information in DNS messages.  The option is structured as
   follows:

                                                1   1   1   1   1   1
        0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   0: |                            OPTION-CODE                        |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   2: |                           OPTION-LENGTH                       |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   4: | INFO-CODE                                                     |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   6: / EXTRA-TEXT ...                                                /
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

   Field definition details:

   o  OPTION-CODE, 2-octets/16-bits (defined in [RFC6891]]), for EDE is
      TBD.  [RFC Editor: change TBD to the proper code once assigned by
      IANA.]
   o  OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]]) contains
      the length of the payload (everything after OPTION-LENGTH) in
      octets and should be 2 plus the length of the EXTRA-TEXT field
      (which may be a zero-length string).
   o  INFO-CODE, 16-bits, which is the principal contribution of this
      document.  This 16-bit value, encoded in network (MSB) byte order,
      provides the additional context for the RESPONSE-CODE of the DNS
      message.  The INFO-CODE serves as an index into the "Extended DNS
      Errors" registry defined and created in Section 5.2.
   o  EXTRA-TEXT, a variable length, UTF-8 encoded [RFC5198], text field
      that may hold additional textual information.  This information is
      intended for human consumption (not automated parsing).  EDE text
      may be null terminated but MUST NOT be assumed to be; the length
      MUST be derived from the OPTION-LENGTH field.  The EXTRA-TEXT
      field may be zero octets in length, indicating that there is no
      EXTRA-TEXT included.  Care should be taken not to include private
      information in the EXTRA-TEXT field that an observer would not
      otherwise have access to, such as account numbers.

   The Extended DNS Error (EDE) option can be included in any response
   (SERVFAIL, NXDOMAIN, REFUSED, and even NOERROR, etc) to a query that
   includes OPT Pseudo-RR [RFC6891].  This document includes a set of



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   initial codepoints, but is extensible via the IANA registry defined
   and created in Section 5.2.

3.  Extended DNS Error Processing

   When the response grows beyond the requestor's UDP payload size
   [RFC6891], servers SHOULD truncate messages by dropping EDE options
   before dropping other data from packets.  Implementations SHOULD set
   the truncation bit when dropping EDE options.  Because long EXTRA-
   TEXT fields may trigger truncation (which is undesirable given the
   supplemental nature of EDE) implementers and operators creating EDE
   options SHOULD avoid lengthy EXTRA-TEXT contents.

   When a resolver or forwarder receives an EDE option, whether or not
   (and how) to pass along EDE information on to their original client
   is implementation dependent.  Implementations MAY choose to not
   forward information, or they MAY choose to create a new EDE option(s)
   that conveys the information encoded in the received EDE.  When doing
   so, the source of the error SHOULD be attributed in the EXTRA-TEXT
   field, since an EDNS0 option received by the original client will
   appear to have come from the resolver or forwarder sending it.

   This document does not allow or prohibit any particular extended
   error codes and information to be matched with any particular RCODEs.
   Some combinations of extended error codes and RCODEs may seem
   nonsensical (such as resolver-specific extended error codes in
   responses from authoritative servers), so systems interpreting the
   extended error codes MUST NOT assume that a combination will make
   sense.  Receivers MUST be able to accept EDE codes and EXTRA-TEXT in
   all messages, including those with a NOERROR RCODE, but need not act
   on them.  Applications MUST continue to follow requirements from
   applicable specifications on how to process RCODEs no matter what EDE
   values are also received.  Senders MAY include more than one EDE
   option and receivers MUST be able to accept (but not necessarily
   process or act on) multiple EDE options in a DNS message.

4.  Defined Extended DNS Errors

   This document defines some initial EDE codes.  The mechanism is
   intended to be extensible, and additional code-points can be
   registered in the "Extended DNS Errors" registry Section 5.2.  The
   INFO-CODE from the EDE EDNS option is used to serve as an index into
   the "Extended DNS Error" IANA registry, the initial values for which
   are defined in the following sub-sections.







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4.1.  Extended DNS Error Code 0 - Other

   The error in question falls into a category that does not match known
   extended error codes.  Implementations SHOULD include an EXTRA-TEXT
   value to augment this error code with additional information.

4.2.  Extended DNS Error Code 1 - Unsupported DNSKEY Algorithm

   The resolver attempted to perform DNSSEC validation, but a DNSKEY
   RRSET contained only unsupported DNSSEC algorithms.

4.3.  Extended DNS Error Code 2 - Unsupported DS Digest Type

   The resolver attempted to perform DNSSEC validation, but a DS RRSET
   contained only unsupported Digest Types.

4.4.  Extended DNS Error Code 3 - Stale Answer

   The resolver was unable to resolve the answer within its time limits
   and decided to answer with previously cached data instead of
   answering with an error.  This is typically caused by problems
   communicating with an authoritative server, possibly as result of a
   denial of service (DoS) attack against another network.  (See also
   Code 19.)

4.5.  Extended DNS Error Code 4 - Forged Answer

   For policy reasons (legal obligation, or malware filtering, for
   instance), an answer was forged.  Note that this should be used when
   an answer is still provided, not when failure codes are returned
   instead.  See Blocked(15), Censored (16), and Filtered (17) for use
   when returning other response codes.

4.6.  Extended DNS Error Code 5 - DNSSEC Indeterminate

   The resolver attempted to perform DNSSEC validation, but validation
   ended in the Indeterminate state [RFC4035].

4.7.  Extended DNS Error Code 6 - DNSSEC Bogus

   The resolver attempted to perform DNSSEC validation, but validation
   ended in the Bogus state.

4.8.  Extended DNS Error Code 7 - Signature Expired

   The resolver attempted to perform DNSSEC validation, but no
   signatures are presently valid and some (often all) are expired.




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4.9.  Extended DNS Error Code 8 - Signature Not Yet Valid

   The resolver attempted to perform DNSSEC validation, but but no
   signatures are presently valid and at least some are not yet valid.

4.10.  Extended DNS Error Code 9 - DNSKEY Missing

   A DS record existed at a parent, but no supported matching DNSKEY
   record could be found for the child.

4.11.  Extended DNS Error Code 10 - RRSIGs Missing

   The resolver attempted to perform DNSSEC validation, but no RRSIGs
   could be found for at least one RRset where RRSIGs were expected.

4.12.  Extended DNS Error Code 11 - No Zone Key Bit Set

   The resolver attempted to perform DNSSEC validation, but no Zone Key
   Bit was set in a DNSKEY.

4.13.  Extended DNS Error Code 12 - NSEC Missing

   The resolver attempted to perform DNSSEC validation, but the
   requested data was missing and a covering NSEC or NSEC3 was not
   provided.

4.14.  Extended DNS Error Code 13 - Cached Error

   The resolver is returning the SERVFAIL RCODE from its cache.

4.15.  Extended DNS Error Code 14 - Not Ready

   The server is unable to answer the query as it was not fully
   functional when the query was received.

4.16.  Extended DNS Error Code 15 - Blocked

   The server is unable to respond to the request because the domain is
   blacklisted due to an internal security policy imposed by the
   operator of the server resolving or forwarding the query.

4.17.  Extended DNS Error Code 16 - Censored

   The server is unable to respond to the request because the domain is
   blacklisted due to an external requirement imposed by an entity other
   than the operator of the server resolving or forwarding the query.
   Note that how the imposed policy is applied is irrelevant (in-band
   DNS filtering, court order, etc).



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4.18.  Extended DNS Error Code 17 - Filtered

   The server is unable to respond to the request because the domain is
   blacklisted as requested by the client.  Functionally, this amounts
   to "you requested that we filter domains like this one."

4.19.  Extended DNS Error Code 18 - Prohibited

   An authoritative server or recursive resolver that receives a query
   from an "unauthorized" client can annotate its REFUSED message with
   this code.  Examples of "unauthorized" clients are recursive queries
   from IP addresses outside the network, blacklisted IP addresses,
   local policy, etc.

4.20.  Extended DNS Error Code 19 - Stale NXDOMAIN Answer

   The resolver was unable to resolve an answer within its configured
   time limits and decided to answer with a previously cached NXDOMAIN
   answer instead of answering with an error.  This may be caused, for
   example, by problems communicating with an authoritative server,
   possibly as result of a denial of service (DoS) attack against
   another network.  (See also Code 3.)

4.21.  Extended DNS Error Code 20 - Not Authoritative

   An authoritative server that receives a query with the RD bit clear,
   or when it is not configured for recursion for a domain for which it
   is not authoritative SHOULD include this EDE code in the REFUSED
   response.  A resolver that receives a query with the RD bit clear
   SHOULD include this EDE code in the REFUSED response.

4.22.  Extended DNS Error Code 21 - Not Supported

   The requested operation or query is not supported.

4.23.  Extended DNS Error Code 22 - No Reachable Authority

   The resolver could not reach any of the authoritative name servers
   (or they potentially refused to reply).

4.24.  Extended DNS Error Code 23 - Network Error

   An unrecoverable error occurred while communicating with another
   server.







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4.25.  Extended DNS Error Code 24 - Invalid Data

   The authoritative server cannot answer with data for a zone it is
   otherwise configured to support.  Examples of this include its most
   recent zone being too old, or having expired.

5.  IANA Considerations

5.1.  A New Extended DNS Error Code EDNS Option

   This document defines a new EDNS(0) option, entitled "Extended DNS
   Error", assigned a value of TBD from the "DNS EDNS0 Option Codes
   (OPT)" registry [to be removed upon publication:
   [http://www.iana.org/assignments/dns-parameters/dns-
   parameters.xhtml#dns-parameters-11]

   Value  Name                 Status    Reference
   -----  ----------------     ------    ------------------
    TBD   Extended DNS Error    Standard       [ This document ]

5.2.  New Registry for Extended DNS Error Codes

   IANA is requested to create and maintain a new registry table called
   "Extended DNS Error Codes" on the "Domain Name System (DNS)
   Parameters" web page as follows:

   Registry Name: Extended DNS Error Codes

   Registration Procedures:

   o  0 - 49151: First come, first served.
   o  49152 - 65535: Private use.

   Reference: [this document]

   The Extended DNS Error Codes registry is a table with three columns:
   INFO-CODE, Purpose, and Reference.  The initial contents is as below
   with [this document] added to each reference given.

   INFO-CODE:  0
   Purpose:  Other Error
   Reference:  Section 4.1

   INFO-CODE:  1
   Purpose:  Unsupported DNSKEY Algorithm
   Reference:  Section 4.2

   INFO-CODE:  2



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   Purpose:  Unsupported DS Digest Type
   Reference:  Section 4.3

   INFO-CODE:  3
   Purpose:  Stale Answer
   Reference:  Section 4.4, [RFC8767]

   INFO-CODE:  4
   Purpose:  Forged Answer
   Reference:  Section 4.5

   INFO-CODE:  5
   Purpose:  DNSSEC Indeterminate
   Reference:  Section 4.6

   INFO-CODE:  6
   Purpose:  DNSSEC Bogus
   Reference:  Section 4.7

   INFO-CODE:  7
   Purpose:  Signature Expired
   Reference:  Section 4.8

   INFO-CODE:  8
   Purpose:  Signature Not Yet Valid
   Reference:  Section 4.9

   INFO-CODE:  9
   Purpose:  DNSKEY Missing
   Reference:  Section 4.10

   INFO-CODE:  10
   Purpose:  RRSIGs Missing
   Reference:  Section 4.11

   INFO-CODE:  11
   Purpose:  No Zone Key Bit Set
   Reference:  Section 4.12

   INFO-CODE:  12
   Purpose:  NSEC Missing
   Reference:  Section 4.13

   INFO-CODE:  13
   Purpose:  Cached Error
   Reference:  Section 4.14

   INFO-CODE:  14



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   Purpose:  Not Ready.
   Reference:  Section 4.15

   INFO-CODE:  15
   Purpose:  Blocked
   Reference:  Section 4.16

   INFO-CODE:  16
   Purpose:  Censored
   Reference:  Section 4.17

   INFO-CODE:  17
   Purpose:  Filtered
   Reference:  Section 4.18

   INFO-CODE:  18
   Purpose:  Prohibited
   Reference:  Section 4.19

   INFO-CODE:  19
   Purpose:  Stale NXDomain Answer
   Reference:  Section 4.20

   INFO-CODE:  20
   Purpose:  Not Authoritative
   Reference:  Section 4.21

   INFO-CODE:  21
   Purpose:  Not Supported
   Reference:  Section 4.22

   INFO-CODE:  22
   Purpose:  No Reachable Authority
   Reference:  Section 4.23

   INFO-CODE:  23
   Purpose:  Network Error
   Reference:  Section 4.24

   INFO-CODE:  24
   Purpose:  Invalid Data
   Reference:  Section 4.25

   INFO-CODE:  25-65535
   Purpose:  Unassigned
   Reference:  Section 5.2





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6.  Security Considerations

   Though DNSSEC continues to be deployed, unfortunately a significant
   number of clients (~11% according to [GeoffValidation]) that receive
   a SERVFAIL from a validating resolver because of a DNSSEC validation
   issue will simply ask the next (potentially non-validating) resolver
   in their list, and thus don't get the protections which DNSSEC should
   provide.

   EDE information is unauthenticated information, unless secured by a
   form of secured DNS transaction such as [RFC2845], [RFC2931],
   [RFC8094] or [RFC8484].  An attacker (e.g a MITM or malicious
   recursive server) could insert an extended error response into
   untrusted data -- although ideally clients and resolvers would not
   trust any unauthenticated information.  As such, EDE content should
   be treated only as diagnostic information and MUST NOT alter DNS
   protocol processing.  Until all DNS answers are authenticated via
   DNSSEC or the other mechanisms mentioned above, there are some
   tradeoffs.  As an example, an attacker who is able to insert the
   DNSSEC Bogus Extended Error into a DNS message could instead simply
   reply with a fictitious address (A or AAAA) record.  Note that DNS
   Response Codes (RCODEs) also contain no authentication and can be
   just as easily manipulated.

   By design, EDE potentially exposes additional information DNS
   resolution processes that may leak information.  An example of this
   is the Prohibited EDE code (18), which may leak the fact that the
   name is on a blacklist.

7.  Acknowledgements

   The authors wish to thank Joe Abley, Mark Andrews, Tim April,
   Vittorio Bertola, Stephane Bortzmeyer, Vladimir Cunat, Ralph Dolmans,
   Peter DeVries, Peter van Dijk, Mats Dufberg, Donald Eastlake, Bob
   Harold, Paul Hoffman, Geoff Huston, Shane Kerr, Edward Lewis, Carlos
   M.  Martinez, George Michelson, Eric Orth, Michael Sheldon, Puneet
   Sood, Petr Spacek, Ondrej Sury, John Todd, Loganaden Velvindron, and
   Paul Vixie.  They also vaguely remember discussing this with a number
   of people over the years, but have forgotten who all they were -- if
   you were one of them, and are not listed, please let us know and
   we'll acknowledge you.

   One author also wants to thank the band "Infected Mushroom" for
   providing a good background soundtrack (and to see if he can get away
   with this in an RFC!).  Another author would like to thank the band
   "Mushroom Infectors".  This was funny at the time we wrote it, but we
   cannot remember why...




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8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
              <https://www.rfc-editor.org/info/rfc4035>.

   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <https://www.rfc-editor.org/info/rfc5198>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

   [RFC8767]  Lawrence, D., Kumari, W., and P. Sood, "Serving Stale Data
              to Improve DNS Resiliency", RFC 8767,
              DOI 10.17487/RFC8767, March 2020,
              <https://www.rfc-editor.org/info/rfc8767>.

8.2.  Informative References

   [GeoffValidation]
              APNIC, G. H., "A quick review of DNSSEC Validation in
              today's Internet", June 2016, <http://www.potaroo.net/
              presentations/2016-06-27-dnssec.pdf>.

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
              <https://www.rfc-editor.org/info/rfc2845>.




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   [RFC2931]  Eastlake 3rd, D., "DNS Request and Transaction Signatures
              ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
              2000, <https://www.rfc-editor.org/info/rfc2931>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <https://www.rfc-editor.org/info/rfc8094>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

Authors' Addresses

   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: warren@kumari.net


   Evan Hunt
   ISC
   950 Charter St
   Redwood City, CA  94063
   US

   Email: each@isc.org


   Roy Arends
   ICANN

   Email: roy.arends@icann.org


   Wes Hardaker
   USC/ISI
   P.O. Box 382
   Davis, CA  95617
   US

   Email: ietf@hardakers.net





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   David C Lawrence
   Oracle + Dyn
   150 Dow St
   Manchester, NH  03101
   US

   Email: tale@dd.org












































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