Structured Error Data for Filtered DNS
draft-ietf-dnsop-structured-dns-error-00

DNS Operations Working Group                                     D. Wing
Internet-Draft                                                    Citrix
Updates: 8914 (if approved)                                     T. Reddy
Intended status: Standards Track                                   Nokia
Expires: 17 August 2023                                          N. Cook
                                                            Open-Xchange
                                                            M. Boucadair
                                                                  Orange
                                                        13 February 2023

                 Structured Error Data for Filtered DNS
                draft-ietf-dnsop-structured-dns-error-00

Abstract

   DNS filtering is widely deployed for network security, but filtered
   DNS responses lack information for the end user to understand the
   reason for the filtering.  Existing mechanisms to provide detail to
   end users cause harm especially if the blocked DNS response is to an
   HTTPS website.

   This document updates RFC 8914 by structuring the EXTRA-TEXT field of
   the Extended DNS Error to provide details on the DNS filtering.  Such
   details can be parsed by the client and displayed, logged, or used
   for other purposes.  Other than that, this document does not change
   any thing written in RFC 8914.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at https://ietf-wg-
   dnsop.github.io/draft-ietf-dnsop-structured-dns-error/draft-ietf-
   dnsop-structured-dns-error.html.  Status information for this
   document may be found at https://datatracker.ietf.org/doc/draft-ietf-
   dnsop-structured-dns-error/.

   Discussion of this document takes place on the dnsop Working Group
   mailing list (mailto:dnsop@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/dnsop/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/dnsop/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-dnsop/draft-ietf-dnsop-structured-dns-
   error.

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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 17 August 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   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/
   license-info) in effect on the date of publication of this document.
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  DNS Filtering Techniques and Their Limitations  . . . . . . .   4
   4.  I-JSON in EXTRA-TEXT field  . . . . . . . . . . . . . . . . .   6
   5.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Client Generating Request . . . . . . . . . . . . . . . .   7
     5.2.  Server Generating Response  . . . . . . . . . . . . . . .   8
     5.3.  Client Processing Response  . . . . . . . . . . . . . . .   8
   6.  Interoperation with RPZ Servers . . . . . . . . . . . . . . .   9
   7.  New Sub-Error Codes Definition  . . . . . . . . . . . . . . .  10
     7.1.  Reserved  . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.2.  Network Operator Policy . . . . . . . . . . . . . . . . .  10
     7.3.  DNS Operator Policy . . . . . . . . . . . . . . . . . . .  11
   8.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  12

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   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  New structured-dns-error Media Type  . . . . . . . . . .  12
     10.2.  New Registry for SubError Codes  . . . . . . . . . . . .  13
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     11.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   DNS filters are deployed for a variety of reasons including endpoint
   security, parental filtering, and filtering required by law
   enforcement.  Network-based security solutions such as firewalls and
   Intrusion Prevention Systems (IPS) rely upon network traffic
   inspection to implement perimeter-based security policies and operate
   by filtering DNS responses.  In a home, DNS filtering is used for the
   same reasons as above and additionally for parental control.
   Internet Service Providers typically block access to some DNS domains
   due to a requirement imposed by an external entity (e.g., law
   enforcement agency) also performed using DNS-based content filtering.

   Users of DNS services which perform filtering may wish to receive
   more information about such filtering to resolve problems with the
   filter -- for example to contact the administrator to allowlist a
   domain that was erroneously filtered or to understand the reason a
   particular domain was filtered.  With that information, the user can
   choose another network, open a trouble ticket with the DNS
   administrator to resolve erroneous filtering, log the information, or
   other uses.

   For the DNS filtering mechanisms described in Section 3 the DNS
   server can return extended error codes Blocked, Censored, Filtered,
   or Forged Answer defined in Section 4 of [RFC8914].  However, these
   codes only explain that filtering occurred but lack detail for the
   user to diagnose erroneous filtering.

   No matter which type of response is generated (forged IP address(es),
   NXDOMAIN or empty answer, even with an extended error code), the user
   who triggered the DNS query has little chance to understand which
   entity filtered the query, how to report a mistake in the filter, or
   why the entity filtered it at all.  This document describes a
   mechanism to provide such detail.

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   One of the other benefits of this approach is to eliminate the need
   to "spoof" block pages for HTTPS resources.  This is achieved since
   clients implementing this approach would be able to display a
   meaningful error message, and would not need to connect to such a
   block page.  This approach thus avoids the need to install a local
   root certificate authority on those IT-managed devices.

   This document describes a format for computer-parsable data in the
   EXTRA-TEXT field of [RFC8914].  It updates Section 2 of [RFC8914]
   which says the information in EXTRA-TEXT field is intended for human
   consumption (not automated parsing).

   This document does not recommend DNS filtering but provides a
   mechanism for better transparency to explain to the users why some
   DNS queries are filtered.

2.  Conventions and Definitions

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

   This document uses terms defined in DNS Terminology [RFC8499].

   "Requestor" refers to the side that sends a request.  "Responder"
   refers to an authoritative, recursive resolver or other DNS component
   that responds to questions.  Other terminology is used here as
   defined in the RFCs cited by this document.

   "Encrypted DNS" refers to any encrypted scheme to convey DNS
   messages, for example, DNS-over-HTTPS [RFC8484], DNS-over-TLS
   [RFC7858], or DNS-over-QUIC [RFC9250].

   The document refers to an extended DNS error using its purpose, not
   its INFO-CODE as per Table 3 of [RFC8914].  "Forged Answer",
   "Blocked", "Censored", and "Filtered" are thus used to refer to
   "Forged Answer (4)", "Blocked (15)", "Censored (16)", and "Filtered
   (17)".

3.  DNS Filtering Techniques and Their Limitations

   Today, DNS responses can be filtered by sending a bogus (also called
   "forged") A or AAAA response, NXDOMAIN error or empty answer, or an
   extended DNS error (EDE) code defined in [RFC8914].  Each of these
   methods have advantages and disadvantages that are discussed below:

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   1.  The DNS response is forged to provide a list of IP addresses that
       points to an HTTP(S) server alerting the end user about the
       reason for blocking access to the requested domain (e.g.,
       malware).  When an HTTP(S) enabled domain name is blocked, the
       network security device (e.g., CPE, firewall) presents a block
       page instead of the HTTP response from the content provider
       hosting that domain.  If an HTTP enabled domain name is blocked,
       the network security device intercepts the HTTP request and
       returns a block page over HTTP.  If an HTTPS enabled domain is
       blocked, the block page is also served over HTTPS.  In order to
       return a block page over HTTPS, man in the middle (MITM) is
       enabled on endpoints by generating a local root certificate and
       an accompanying (local) public/private key pair.  The local root
       certificate is installed on the endpoint while the network
       security device(s) stores a copy of the private key.  During the
       TLS handshake, the network security device modifies the
       certificate provided by the server and (re)signs it using the
       private key from the local root certificate.

       *  However, configuring the local root certificate on endpoints
          is not a viable option in several deployments like home
          networks, schools, Small Office/Home Office (SOHO), and Small/
          Medium Enterprise (SME).  In these cases, the typical behavior
          is that the filtered DNS response points to a server that will
          display the block page.  If the client is using HTTPS (via web
          browser or another application) this results in a certificate
          validation error which gives no information to the end-user
          about the reason for the DNS filtering.  Browsers will display
          errors such as "The security certificate presented by this
          website was not issued by a trusted certificate authority"
          (Internet Explorer/Edge"), "The site's security certificate is
          not trusted" (Chrome), "This Connection is Untrusted"
          (Firefox), "Safari can't verify the identity of the website
          ..." (Safari on MacOS).  Applications might display even more
          cryptic error messages.

       *  Enterprise networks do not assume that all the connected
          devices are managed by the IT team or Mobile Device Management
          (MDM) devices, especially in the quite common Bring Your Own
          Device (BYOD) scenario.  In addition, the local root
          certificate cannot be installed on IoT devices without a
          device management tool.

       *  An end user does not know why the connection was prevented
          and, consequently, may repeatedly try to reach the domain but
          with no success.  Frustrated, the end user may switch to an
          alternate network that offers no DNS filtering against malware
          and phishing, potentially compromising both security and

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          privacy.  Furthermore, certificate errors train users to click
          through certificate errors, which is a bad security practice.
          To eliminate the need for an end user to click through
          certificate errors, an end user may manually install a local
          root certificate on a host device.  Doing so, however, is also
          a bad security practice as it creates a security vulnerability
          that may be exploited by a MITM attack.  When a manually
          installed local root certificate expires, the user has to
          (again) manually install the new local root certificate.

   2.  The DNS response is forged to provide a NXDOMAIN response to
       cause the DNS lookup to terminate in failure.  In this case, an
       end user does not know why the domain cannot be reached and may
       repeatedly try to reach the domain but with no success.
       Frustrated, the end user may use insecure connections to reach
       the domain, potentially compromising both security and privacy.

   3.  The extended error codes Blocked, Censored, and Filtered defined
       in Section 4 of [RFC8914] can be returned by a DNS server to
       provide additional information about the cause of an DNS error.
       If the extended error code "Forged Answer" defined in Section 4.5
       of [RFC8914] is returned by the DNS server, the client can
       identify the DNS response is forged together with the reason for
       HTTPS certificate error.

   4.  These extended error codes do not suffer from the limitations
       discussed in bullets (1) and (2), but the user still does not
       know the exact reason nor he/she is aware of the exact entity
       blocking the access to the domain.  For example, a DNS server may
       block access to a domain based on the content category such as
       "Malware" to protect the endpoint from malicious software,
       "Phishing" to prevent the user from revealing sensitive
       information to the attacker, etc.  A user needs to know the
       contact details of the IT/InfoSec team to raise a complaint.

   5.  When a resolver or forwarder forwards the received EDE option,
       the EXTRA-TEXT field only conveys the source of the error
       (Section 3 of [RFC8914]) and does not provide additional textual
       information about the cause of the error.

4.  I-JSON in EXTRA-TEXT field

   Servers that are compliant with this specification send I-JSON data
   in the EXTRA-TEXT field [RFC8914] using the Internet JSON (I-JSON)
   message format [RFC7493].

      Note that [RFC7493] was based on [RFC7159], but [RFC7159] was
      replaced by [RFC8259].

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   This document defines the following JSON names:

   c: (contact)  The contact details of the IT/InfoSec team to report
      mis-classified DNS filtering.  This field is structured as an
      array of contact URIs (e.g., tel, sips, https).  At least one
      contact URI MUST be included.  This field is mandatory.

   j: (justification)  UTF-8-encoded [RFC5198] textual justification for
      this particular DNS filtering.  The field should be treated only
      as diagnostic information for IT staff.  This field is mandatory.

   s: (suberror)  the suberror code for this particular DNS filtering.
      This field is optional.

   o: (organization)  UTF-8-encoded human-friendly name of the
      organization that filtered this particular DNS query.  This field
      is optional.

   New JSON names can be defined in the IANA "application/
   json+structured-dns-error" registry (Section 10).  Such names MUST
   consist only of lower-case ASCII characters, digits, and hyphens
   (that is, Unicode characters U+0061 through 007A, U+0030 through
   U+0039, and U+002D).  Also, these names MUST be 63 characters or
   shorter and it is RECOMMENDED they be as short as possible.

   The text in the "j" and "o" names can include international
   characters.  If the text is displayed in a language not known to the
   end user, browser extensions to translate to user's native language
   can be used.  For example, "Google Translate" extension
   [Chrome-Translate] provided by Google on Chrome can be used to
   translate the text.

   To reduce packet overhead the generated JSON SHOULD be as short as
   possible: short domain names, concise text in the values for the "j"
   and "o" names, and minified JSON (that is, without spaces or line
   breaks between JSON elements).

   The JSON data can be parsed to display to the user, logged, or
   otherwise used to assist the end-user or IT staff with
   troubleshooting and diagnosing the cause of the DNS filtering.

5.  Protocol Operation

5.1.  Client Generating Request

   When generating a DNS query, the client includes the Extended DNS
   Error option Section 2 of [RFC8914] in the OPT pseudo-RR [RFC6891] to
   elicit the Extended DNS Error option in the DNS response.

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5.2.  Server Generating Response

   When the DNS server filters its DNS response to an A or AAAA record
   query, the DNS response MAY contain an empty answer, NXDOMAIN, or
   (less ideally) forged A or AAAA response, as desired by the DNS
   server.  In addition, if the query contained the OPT pseudo-RR the
   DNS server MAY return more detail in the EXTRA-TEXT field as
   described in Section 5.3.

   Servers may decide to return small TTL values in filtered DNS
   responses (e.g., 2 seconds) to handle domain category and reputation
   updates.

   Because the DNS client signals its EDE support (Section 5.1) and
   because EDE support is signaled via a non-cached OPT resource record
   (Section 6.2.1 of [RFC6891]) the EDE-aware DNS server can tailor its
   filtered response to be most appropriate to that client's EDE
   support.  If EDE support is signaled in the query the server MUST NOT
   return the "Forged Answer" extended error code because the client can
   take advantage of EDE's more sophisticated error reporting (e.g.,
   "Censored", "Filtered", "Blocked").  Continuing to send "Forged
   Answer" even to an EDE-supporting client will cause the persistence
   of the drawbacks described in Section 3.

5.3.  Client Processing Response

   On receipt of a DNS response with an Extended DNS Error option, the
   following actions are performed if the EXTRA-TEXT field contains
   valid JSON:

   *  The response MUST be received over an encrypted DNS channel.  If
      not, the requestor MUST discard data in the EXTRA-TEXT field.

   *  The response MUST be received from a DNS server which advertised
      EDE support via a trusted channel, e.g., RESINFO
      [I-D.reddy-add-resolver-info].

   *  Servers which don't support this specification might use plain
      text in the EXTRA-TEXT field so that requestors SHOULD properly
      handle both plaintext and JSON text in the EXTRA-TEXT field.

   *  The DNS response MUST also contain an extended error code of
      "Censored", "Blocked", "Filtered" or "Forged Answer" [RFC8914],
      otherwise the EXTRA-TEXT field is discarded.

   *  If either of the mandatory JSON names "c" and "j" are missing or
      have empty values in the EXTRA-TEXT field, the entire JSON is
      discarded.

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   *  The JSON name "s" MUST NOT be present with the extended error code
      "Censored".

   *  If a DNS client has enabled opportunistic privacy profile
      (Section 5 of [RFC8310]) for DoT, the DNS client will either
      fallback to an encrypted connection without authenticating the DNS
      server provided by the local network or fallback to clear text
      DNS, and cannot exchange encrypted DNS messages.  Both of these
      fallback mechanisms adversely impacts security and privacy.  If
      the DNS client has enabled opportunistic privacy profile for DoT,
      the DNS client MUST ignore the EXTRA-TEXT field of the EDE
      responses, but SHOULD process other parts of the response.

   *  If a DNS client has enabled strict privacy profile (Section 5 of
      [RFC8310]) for DoT, the DNS client requires an encrypted
      connection and successful authentication of the DNS server; this
      mitigates both passive eavesdropping and client redirection (at
      the expense of providing no DNS service if an encrypted,
      authenticated connection is not available).  If the DNS client has
      enabled strict privacy profile for DoT, the client MAY process the
      EXTRA-TEXT field of the DNS response.  Note that the strict and
      opportunistic privacy profiles as defined in [RFC8310] only apply
      to DoT; there has been no such distinction made for DoH.

   *  If the DNS client determines that the encrypted DNS server does
      not offer DNS filtering service, it MUST discard the EXTRA-TEXT
      field of the EDE response.  For example, the DNS client can learn
      whether the encrypted DNS resolver performs DNS-based content
      filtering or not by retrieving resolver information using the
      method defined in [I-D.reddy-add-resolver-info].

   *  When a forwarder receives an EDE option, whether or not (and how)
      to pass along JSON information in the EXTRA-TEXT on to their
      client is implementation dependent [RFC5625].  Implementations MAY
      choose to not forward the JSON information, or they MAY choose to
      create a new EDE option that conveys the information in the "c",
      "s" and "j" fields encoded in the JSON object.

6.  Interoperation with RPZ Servers

   This section discusses operation with an RPZ server [RPZ] that
   indicates filtering with a NXDOMAIN response with the Recursion
   Available bit cleared (RA=0).

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   When the DNS client supports this specification but the server does
   not, the server will continue replying when a query is RPZ filtered
   with NXDOMAIN and RA=0.  An DNS client upgraded to support this
   specification can continue to accept responses with NXDOMAIN and RA=0
   from the RPZ server that does not support this specification.

   When the DNS client supports this specification and the server
   supports this specification, the client learns of the server's
   support via [I-D.reddy-add-resolver-info] and the client includes the
   EDE OPT pseudo-RR in the query.  This allows the server to
   differentiate EDE-aware clients from EDE-unaware clients and respond
   appropriately.

7.  New Sub-Error Codes Definition

   The document defines the following new IANA-registered Sub-Error
   codes.

7.1.  Reserved

   *  Number: 0

   *  Meaning: Reserved.  This sub-error code value MUST NOT be sent.
      If received, it has no meaning.

   *  Applicability: This code should never be used

   *  Reference: This-Document

   *  Change Controller: IETF

7.2.  Network Operator Policy

   *  Number: 5

   *  Meaning: Network Operator Policy.  The code indicates that the
      request was filtered according to policy determined by the
      operator of the local network.

   *  Applicability: Blocked, Forged

   *  Reference: This-Document

   *  Change Controller: IETF

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7.3.  DNS Operator Policy

   *  Number: 6

   *  Meaning: DNS Operator Policy.  The code indicates that the request
      was filtered according to policy determined by the operator of the
      DNS server.

   *  Applicability: Blocked, Forged

   *  Reference: This-Document

   *  Change Controller: IETF

8.  Examples

   An example showing the nameserver at 'ns.example.net' that filtered a
   DNS "A" record query for 'example.org' is shown in Figure 1.

   {
     "c": [
       "tel:+358-555-1234567",
       "sips:bob@bobphone.example.com",
       "https://ticket.example.com?d=example.org&t=1650560748"
     ],
     "j": "malware present for 23 days",
     "s": 1,
     "o": "example.net Filtering Service"
   }

     Figure 1: JSON returned in EXTRA-TEXT field of Extended DNS Error
                                  response

   In Figure 2 the same content is shown with minified JSON (no
   whitespace, no blank lines) with '\' line wrapping per [RFC8792].

    ============== NOTE: '\' line wrapping per RFC 8792 ===============

     {"c":["tel:+358-555-1234567","sips:bob@bobphone.example.com", \
     "https://ticket.example.com?d=example.org&t=1650560748"],"s":1, \
     "j":"malware present for 23 days","o":"example.net Filtering \
     Service"}

                        Figure 2: Minified response

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9.  Security Considerations

   Security considerations in Section 6 of [RFC8914] apply to this
   document.

   To minimize impact of active on-path attacks on the DNS channel, the
   client validates the response as described in Section 5.3.

   A client might choose to display the information in the "c", "j" and
   "o" fields if and only if the encrypted resolver has sufficient
   reputation, according to some local policy (e.g. user configuration,
   administrative configuration, or a built-in list of respectable
   resolvers).  This limits the ability of a malicious encrypted
   resolver to cause harm.  If the client decides not to display the all
   of the information in the EXTRA-TEXT field, it can be logged for
   diagnostics purpose and the client can only display the resolver
   hostname that blocked the domain, error description for the EDE code
   and the suberror description for the "s'" field to the end-user.

   When displaying the free-form text of "c" and "o", the browser SHOULD
   NOT make any of those elements into actionable (clickable) links.

   An attacker might inject (or modify) the EDE EXTRA-TEXT field with an
   DNS proxy or DNS forwarder that is unaware of EDE.  Such a DNS proxy
   or DNS forwarder will forward that attacker-controlled EDE option.
   To prevent such an attack, clients supporting this document MUST
   discard the EDE option if their DNS server does not signal EDE
   support via RESINFO [I-D.reddy-add-resolver-info].  As recommended in
   [I-D.reddy-add-resolver-info], RESINFO should be retrieved over an
   encrypted DNS channel or integrity protected with DNSSEC.

10.  IANA Considerations

   This document requests two IANA actions as described in the following
   subsections.

10.1.  New structured-dns-error Media Type

   This document requests IANA to register the "application/
   json+structured-dns-error" media type in the "Media Types" registry
   [IANA-MediaTypes].  This registration follows the procedures
   specified in [RFC6838]:

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      Type name: application

      Subtype name: json+structured-dns-error

      Required parameters: N/A

      Optional parameters: N/A

      Encoding considerations: as defined in Section NN of [RFCXXXX].

      Security considerations: See Section NNN of [RFCXXXX].

      Interoperability considerations: N/A

      Published specification: [RFCXXXX]

      Applications that use this media type: Section NNNN of [RFCXXXX].

      Fragment identifier considerations: N/A

      Additional information: N/A

      Person & email address to contact for further information: IETF,
         iesg@ietf.org

      Intended usage: COMMON

      Restrictions on usage: none

      Author: See Authors' Addresses section.

      Change controller: IESG

      Provisional registration?  No

10.2.  New Registry for SubError Codes

   This document requests IANA to create a new registry, entitled
   "SubError Codes" under "Domain Name System (DNS) Parameters, Extended
   DNS Error Codes" registry [IANA-DNS].  The registration request for a
   new suberror codes MUST include the following fields:

   *  Number: Wire format suberror code (range 0-255)

   *  Meaning: A short description of the sub-error

   *  Applicability: Indicates which RFC8914 error codes apply to this
      sub-error code

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   *  Reference: A pointer to IETF-approved specification that
      registered the code and/or an authoritative specification that
      describes the meaning of this code

   *  Change Controller: Person or entity, with contact information if
      appropriate.

   The SubError Code registry shall initially be populated with the
   following suberror codes:

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    +========+==========+==================+=============+============+
    | Number | Meaning  | RFC8914 error    | Reference   |   Change   |
    |        |          | code             |             | Controller |
    |        |          | applicability    |             |            |
    +========+==========+==================+=============+============+
    |   0    | Reserved | Not used         | Section 7.1 |    IETF    |
    |        |          |                  | of this     |            |
    |        |          |                  | document    |            |
    +--------+----------+------------------+-------------+------------+
    |   1    | Malware  | "Forged Answer", | Section 5.5 |    IETF    |
    |        |          | "Blocked",       | of          |            |
    |        |          | "Censored",      | [RFC5901]   |            |
    |        |          | "Filtered"       |             |            |
    +--------+----------+------------------+-------------+------------+
    |   2    | Phishing | "Forged Answer", | Section 5.5 |    IETF    |
    |        |          | "Blocked",       | of          |            |
    |        |          | "Censored",      | [RFC5901]   |            |
    |        |          | "Filtered"       |             |            |
    +--------+----------+------------------+-------------+------------+
    |   3    | Spam     | "Forged Answer", | Page 289 of |    IETF    |
    |        |          | "Blocked",       | [RFC4949]   |            |
    |        |          | "Censored",      |             |            |
    |        |          | "Filtered"       |             |            |
    +--------+----------+------------------+-------------+------------+
    |   4    | Spyware  | "Forged Answer", | Page 291 of |    IETF    |
    |        |          | "Blocked",       | [RFC4949]   |            |
    |        |          | "Censored",      |             |            |
    |        |          | "Filtered"       |             |            |
    +--------+----------+------------------+-------------+------------+
    |   5    | Network  | "Forged Answer", | Section 7.2 |    IETF    |
    |        | operator | "Blocked"        | of this     |            |
    |        | policy   |                  | document    |            |
    +--------+----------+------------------+-------------+------------+
    |   6    | DNS      | "Forged Answer", | Section 7.3 |    IETF    |
    |        | operator | "Blocked"        | of this     |            |
    |        | policy   |                  | document    |            |
    +--------+----------+------------------+-------------+------------+

                  Table 1: Initial SubError Code Rregistry

   New entries in this registry are subject to an Expert Review
   registration policy [RFC8126].  The designated expert MUST ensure
   that the Reference is stable and publicly available, and that it
   specifies the suberror code and a short description.  The reference
   may be an individual Internet-Draft, or a document from any other
   source with similar assurances of stability and availability.

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   Review requests are evaluated on the advice of one or more designated
   experts.  Criteria that should be applied by the designated experts
   include determining whether the proposed registration duplicates
   existing entries and whether the registration description is
   sufficiently detailed and fits the purpose of this registry.  The
   designated experts will either approve or deny the registration
   request, communicating this decision to IANA.  Denials should include
   an explanation and, if applicable, suggestions as to how to make the
   request successful.

11.  References

11.1.  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/rfc/rfc2119>.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
              <https://www.rfc-editor.org/rfc/rfc4949>.

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

   [RFC5901]  Cain, P. and D. Jevans, "Extensions to the IODEF-Document
              Class for Reporting Phishing", RFC 5901,
              DOI 10.17487/RFC5901, July 2010,
              <https://www.rfc-editor.org/rfc/rfc5901>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/rfc/rfc6838>.

   [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/rfc/rfc6891>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/rfc/rfc7159>.

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   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/rfc/rfc7493>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/rfc/rfc8126>.

   [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/rfc/rfc8174>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/rfc/rfc8310>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/rfc/rfc8914>.

11.2.  Informative References

   [Chrome-Translate]
              "Change Chrome languages & translate webpages",
              <https://support.google.com/chrome/answer/173424>.

   [I-D.reddy-add-resolver-info]
              Reddy.K, T. and M. Boucadair, "DNS Resolver Information",
              Work in Progress, Internet-Draft, draft-reddy-add-
              resolver-info-06, 31 August 2022,
              <https://datatracker.ietf.org/doc/html/draft-reddy-add-
              resolver-info-06>.

   [IANA-DNS] IANA, "Domain Name System (DNS) Parameters, Extended DNS
              Error Codes", <https://www.iana.org/assignments/dns-
              parameters/dns-parameters.xhtml#extended-dns-error-codes>.

   [IANA-MediaTypes]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",
              BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
              <https://www.rfc-editor.org/rfc/rfc5625>.

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   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/rfc/rfc7858>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/rfc/rfc8259>.

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

   [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/rfc/rfc8499>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/rfc/rfc8792>.

   [RFC9250]  Huitema, C., Dickinson, S., and A. Mankin, "DNS over
              Dedicated QUIC Connections", RFC 9250,
              DOI 10.17487/RFC9250, May 2022,
              <https://www.rfc-editor.org/rfc/rfc9250>.

   [RPZ]      "Response Policy Zone", <https://dnsrpz.info>.

Acknowledgements

   Thanks to Vittorio Bertola, Wes Hardaker, Ben Schwartz, Erid Orth,
   Viktor Dukhovni, Warren Kumari, Paul Wouters, John Levine, and Bob
   Harold for the comments.

Authors' Addresses

   Dan Wing
   Citrix Systems, Inc.
   United States of America
   Email: dwing-ietf@fuggles.com

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   Tirumaleswar Reddy
   Nokia
   Bangalore
   Karnataka
   India
   Email: kondtir@gmail.com

   Neil Cook
   Open-Xchange
   United Kingdom
   Email: neil.cook@noware.co.uk

   Mohamed Boucadair
   Orange
   Rennes
   35000
   France
   Email: mohamed.boucadair@orange.com

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