dnsop                                                          R. Arends
Internet-Draft                                                 M. Larson
Intended status: Standards Track                                   ICANN
Expires: 9 January 2023                                      8 July 2022

                          DNS Error Reporting


   DNS Error Reporting is a lightweight error reporting mechanism that
   provides the operator of an authoritative server with reports on DNS
   resource records that fail to resolve or validate, that a Domain
   Owner or DNS Hosting organization can use to improve domain hosting.
   The reports are based on Extended DNS Errors [RFC8914].

   When a domain name fails to resolve or validate due to a
   misconfiguration or an attack, the operator of the authoritative
   server may be unaware of this.  To mitigate this lack of feedback,
   this document describes a method for a validating recursive resolver
   to automatically signal an error to an agent specified by the
   authoritative server.  DNS Error Reporting uses the DNS to report

   Another lack of feedback occurs when validation was successful, or
   when there is no error to report.  This positive feedback may be
   helpful to show that a deployment was successful.  This document
   introcudes an extended DNS error "NO ERROR".

Status of This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 9 January 2023.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Managing Caching Optimizations  . . . . . . . . . . . . .   5
     4.2.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  EDNS0 Option Specification  . . . . . . . . . . . . . . . . .   6
   6.  DNS Error Reporting Specification . . . . . . . . . . . . . .   7
     6.1.  Reporting Resolver Specification  . . . . . . . . . . . .   7
       6.1.1.  Constructing the Reporting Query  . . . . . . . . . .   7
     6.2.  Authoritative Server Specification  . . . . . . . . . . .   8
     6.3.  Reporting Agent Specification . . . . . . . . . . . . . .   8
     6.4.  Choosing a Reporting Agent Domain . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. Informative References  . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   When an authoritative server serves a stale DNSSEC signed zone, the
   cryptographic signatures over the resource record sets (RRsets) may
   have lapsed.  A validating recursive resolver will fail to validate
   these resource records.

   Similarly, when there is a mismatch between the DS records at a
   parent zone and the key signing key at the child zone, a validating
   recursive resolver will fail to authenticate records in the child

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   These are two of several failure scenarios that may go unnoticed for
   some time by the operator of a zone.

   There is no direct relationship between operators of validating
   recursive resolvers and authoritative servers.  Outages are often
   noticed indirectly, by end users, and reported via social media, if
   reported at all.

   When records fail to validate there is no facility to report this
   failure in an automated way.  If there is any indication that an
   error or warning has happened, it is buried in log files of the
   validating resolver, if these errors are logged at all.

   This document describes a facility that can be used by validating
   recursive resolvers to report errors in an automated way.  In
   addition, successful validation, or a lack of errors can also be
   reported in an automated way.

   It allows an authoritative server to signal a reporting agent where
   the validating recursive resolver can report issues if it is
   configured to do so.  The signal also indicates that the reporting
   agent is interested in successful validation, or lack of errors.

   The burden of reporting a failure falls on the validating recursive
   resolver.  It is important that the effort needed to report failure
   is low, with minimal impact to its main functions.  To accomplish
   this goal, the DNS itself is utilized to report the error.

2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Terminology

   Reporting Resolver: In the context of this document, the term
   reporting resolver is used as a shorthand for a validating recursive
   resolver that supports DNS Error Reporting.

   Reporting Query: The DNS query used to report an error is called a
   reporting query.  A reporting query is for DNS resource record type
   NULL.  The details of the error report are encoded in the QNAME of
   the reporting query.

   Reporting Agent: A facility responsible for receiving error reports
   on behalf of authoritative servers.  This facility is indicated by a
   domain name.

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   Reporting Agent Domain: a domain name which the reporting resolver
   includes in the QNAME of the reporting query.

   Positive Feedback: A report that indicates that no error occurred.

4.  Overview

   An authoritative server indicates support for DNS Error Reporting by
   including an EDNS0 option with OPTION-CODE [TBD] [RFC Editor: change
   TBD to the proper code when assigned by IANA.], a flag to indicate a
   request for positive feedback and the REPORTING AGENT DOMAIN in DNS
   wireformat in the option's payload.  The authoritative server MUST
   NOT include this option in the response if the configured reporting
   agent domain is empty or the null label (the root).

   The positive feedback flag indicates that the reporting agent wants
   to receive extended DNS error [TBD] that indicates that no error
   occurred.  This extended DNS error is defined in this document.

   When a reporting resolver sends a reporting query to report an error,
   it MUST NOT include the EDNS0 Error Reporting option in the reporting
   query.  This avoids additional compounding error reporting when there
   is an issue with the reporting agent domain.

   To report an error, the reporting resolver encodes the error report
   in the QNAME of the reporting query.  The reporting resolver builds
   this QNAME by concatenating the _er label, the extended error code
   [RFC8914], the QTYPE and the QNAME that resulted in failure, the
   label "_er" again, and the reporting agent domain.  See the example
   in section 4.2.

   The resulting concatenated domain name is sent as a standard DNS
   query for DNS resource record type NULL by the reporting resolver.
   This query MUST NOT have the EDNS0 option code [TBD] set to avoid
   compounding error notifications.

   The query will ultimately arrive at the authoritative server for the
   reporting agent domain.  A NODATA negative response is returned by
   the authoritative server of the reporting agent domain, which in turn
   can be cached by the reporting resolver.

   This caching is essential.  It ensures that the number of reports
   sent by a reporting resolver for the same problem is dampened, i.e.
   once per TTL, however, certain optimizations such as [RFC8020] and
   [RFC8198] may reduce the number of error reporting queries as well.

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4.1.  Managing Caching Optimizations

   The reporting resolver may utilize various caching optimizations that
   inhibit subsequent error reporting to the same reporting agent

   If the authoritative server for the reporting agent domain were to
   respond with NXDOMAIN (name error), [RFC8020] rules state that any
   name at or below that domain should be considered unreachable, and
   negative caching would prohibit subsequent queries for anything at or
   below that domain for a period of time, depending on the negative TTL

   Since the authoritative server for an agent domain may not know the
   contents of all the zones it acts as an agent for, it is essential
   that the authoritative server does not respond with NXDOMAIN, as that
   may inhibit subsequent queries.  The use of a wildcard domain name
   [RFC4592] in the zone for the agent domain will ensure the RCODE is
   consistently NOERROR.

   Considering the Resource Record type for this wildcard record, type
   NULL is prohibited in master zone files [RFC1035].  However, any type
   that is not special according to [RFC4592] section 4 will do, such as
   a TXT record with an email address for the reporting agent in the

   Wildcard expansion occurs, even if the QTYPE is not for the type
   owned by the wildcard domain name.  The response is a "no error, but
   no data" response ([RFC4592], section 2.2.1.) that contains a NOERROR
   RCODE and empty answer section.  Note that reporting resolvers are
   not expected to query for this TXT record, since reporting queries
   use type NULL.  This record is solely present to ensure a NODATA
   response is returned in response to reporting queries.

   When the zone for the reporting agent domain is signed, a resolver
   may utilize aggressive negative caching, discussed in [RFC8198].
   This optimization makes use of NSEC and NSEC3 (without opt-out)
   records and allows the resolver to do the wildcard synthesis.  When
   this happens, the resolver may not send subsequent queries as it will
   be able to synthesize a response from previously cached material.

   A solution is to avoid DNSSEC for the reporting agent domain.
   Signing the agent domain will incur an additional burden on the
   reporting resolver, as it has to validate the response.  However,
   this response has no utility to the reporting resolver.

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4.2.  Example

   The domain broken.test is hosted on a set of authoritative servers.
   One of these serves a stale version.  This authoritative server has a
   severity level of 1 and a reporting agent configured: a01.reporting-

   The reporting resolver is unable to validate the broken.test RRSet
   for type A, due to an RRSIG record with an expired signature.

   The reporting resolver constructs the QNAME
   _er.7.1.broken.test._er.a01.reporting-agent.example and resolves it.
   This QNAME indicates extended DNS error 7 occurred while trying to
   validate broken.test type 1 (A) record.

   After this query is received at one of the authoritative servers for
   the reporting agent domain (a01.reporting-agent.example), the
   reporting agent (the operators of the authoritative server for
   a01.reporting-agent.example) determines that the authoritative server
   for the broken.test zone suffers from an expired signature record
   (extended error 7) for type A for the domain name broken.test.  The
   reporting agent can contact the operators of broken.test to fix the

5.  EDNS0 Option Specification

   This method uses an EDNS0 [RFC6891] option to indicate support for
   sending DNS error reports and responding with the Reporting Agent
   Domain in DNS messages.  The option is structured as follows:

                        1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |        OPTION-CODE = TBD      |       OPTION-LENGTH           |
   |F|                  REPORTING AGENT DOMAIN                     /

   Field definition details:

   *  OPTION-CODE, 2-octets/16-bits (defined in [RFC6891]), for
      indicating error reporting support is TBD.  [RFC Editor: change
      TBD to the proper code when assigned by IANA.]

   *  OPTION-LENGTH, 2-octets/16-bits ((defined in [RFC6891]) contains
      the length of the REPORTING AGENT DOMAIN field in octets.

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   *  F, A flag to request positive feedback (i.e. to include the "No
      Error" extended DNS error defined in this document when

   *  REPORTING AGENT DOMAIN, a Domain name [RFC8499] in the DNS wire
      format prescribed by [RFC1035].

6.  DNS Error Reporting Specification

   The various errors that a reporting resolver may encounter are listed
   in [RFC8914].  Note that not all listed errors may be supported by
   the reporting resolver.  This document does not specify what is an
   error and what is not.

   The DNS class is not specified in the error report.

6.1.  Reporting Resolver Specification

   Reporting Resolvers may have a configuration that allows the

   The reporting resolver MUST NOT use DNS error reporting to report a
   failure in resolving the reporting query.

   The reporting resolver MUST NOT use DNS error reporting if the
   authoritative server has an empty Reporting Agent Domain field in the
   EDNS Error Reporting option.

   The reporting resolver should limit the amount of positive feedback

6.1.1.  Constructing the Reporting Query

   The QNAME for the reporting query is constructed by concatenating the
   following elements, appending each successive element in the list to
   the right-hand side of the QNAME:

   *  A label containing the string "_er".

   *  The Extended DNS error, presented as a decimal value, in a single
      DNS label.

   *  The QTYPE that was used in the query that resulted in the extended
      DNS error, presented as a decimal value, in a single DNS label.

   *  The QNAME that was used in the query that resulted in the extended
      DNS error.  The QNAME may consist of multiple labels and is
      concatenated as is, i.e. in DNS wire format.

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   *  A label containing the string "_er".

   *  The reporting agent domain.  The reporting agent domain consists
      of multiple labels and is concatenated exactly as received in the
      EDNS option sent by the authoritative server.

   If the resulting reporting query QNAME would exceed 255 octets, it
   MUST NOT be sent.

   The "_er" labels allow the reporting agent to quickly differentiate
   between the agent domain and the faulty query name.  When the
   specified agent domain is empty, or a NULL label (despite being not
   allowed in this specification), the reporting query will have "_er"
   as a top-level domain as a result and not the original query.
   Lastly, the purpose of the first "_er" label is to indicate that a
   complete reporting query has been received, instead of a shorter
   reporting query due to query minimization.

6.2.  Authoritative Server Specification

   The Authoritative Server SHOULD NOT have multiple reporting agent
   domains configured for a single zone.  To support multiple reporting
   agents, a single agent can act as a syndicate to subsequently inform
   additional agents.

   An authoritative server for a zone with DNS error reporting enabled
   SHOULD NOT also be authoritative for that zone's reporting agent
   domain's zone.

6.3.  Reporting Agent Specification

   It is RECOMMENDED that the reporting agent zone uses a wildcard DNS
   record of type TXT with an arbitrary string in the RDATA and a TTL of
   at least one hour.

6.4.  Choosing a Reporting Agent Domain

   It is RECOMMENDED that the reporting agent domain be kept relatively
   short to allow for a longer QNAME in the reporting query.

7.  IANA Considerations

   IANA is requested to assign the following DNS EDNS0 option code

         Value    Name              Status      Reference
         -----    ----------------  --------    ---------------
         TBD      DNS ERROR REPORT  Standard    [this document]

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   [RFC Editor: change TBD to the proper code when assigned by IANA.]

   IANA is requested to assign the following Underscored and Globally
   Scoped DNS Node Name registry:

         RR Type  _NODE NAME  Reference
         -----    ----------  ---------
         TXT      _er         [this document]

   IANA is requested to assign the following value the "Extended DNS
   Error Codes" registry:


   Purpose: No Error

   Reference: This document

8.  Security Considerations

   Use of DNS Error Reporting may expose local configuration mistakes in
   the reporting resolver, such as stale DNSSEC trust anchors to the
   reporting agent.

   DNS Error reporting SHOULD be done using DNS Query Name Minimization
   [RFC7816] to improve privacy.

   DNS Error Reporting is done without any authentication between the
   reporting resolver and the authoritative server of the agent domain.
   Authentication significantly increases the burden on the reporting
   resolver without any benefit to the reporting agent, authoritative
   server or reporting resolver.

   The method described in this document will cause additional queries
   by the reporting resolver to authoritative servers in order to
   resolve the reporting query.

   This method can be abused by deploying broken zones with agent
   domains that are delegated to servers operated by the intended victim
   in combination with open resolvers [RFC8499].

9.  Acknowledgements

   This document is based on an idea by Roy Arends and David Conrad.
   The authors would like to thank Peter van Dijk, Vladimir Cunat, Paul
   Hoffman, Libor Peltan, Matthijs Mekking, Willem Toorop, Tom Carpay,
   Dick Franks, Benno Overeinder and Petr Spacek for their

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10.  Informative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,

   [RFC4592]  Lewis, E., "The Role of Wildcards in the Domain Name
              System", RFC 4592, DOI 10.17487/RFC4592, July 2006,

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,

   [RFC7816]  Bortzmeyer, S., "DNS Query Name Minimisation to Improve
              Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,

   [RFC8020]  Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is
              Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020,
              November 2016, <https://www.rfc-editor.org/info/rfc8020>.

   [RFC8198]  Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of
              DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198,
              July 2017, <https://www.rfc-editor.org/info/rfc8198>.

   [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>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,

Authors' Addresses

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   Roy Arends
   Email: roy.arends@icann.org

   Matt Larson
   Email: matt.larson@icann.org

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