



Internet Engineering Task Force                             M. Sivaraman
Internet-Draft                              Banu Systems Private Limited
Intended status: Experimental                               1 April 2026
Expires: 3 October 2026


                 EDNS options for filtering information
                      draft-muks-dns-filtering-02

Abstract

   This memo documents EDNS options, EDNS Extended DNS Errors INFO-CODE
   values, and methods that can be used to return information about
   filtered, blocked, or censored DNS responses.  It complements the
   information provided in EDNS Extended DNS Error options [RFC8914].

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
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   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 3 October 2026.

Copyright Notice

   Copyright (c) 2026 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
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   provided without warranty as described in the Revised BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . .   2
   3.  EDE-EXTRA-TEXT-LANGUAGE EDNS option . . . . . . . . . . . . .   3
   4.  FILTERING-CONTACT EDNS option . . . . . . . . . . . . . . . .   3
   5.  FILTERING-ORGANIZATION EDNS option  . . . . . . . . . . . . .   3
   6.  FILTERING-DB EDNS option  . . . . . . . . . . . . . . . . . .   4
   7.  DNS nameserver behavior . . . . . . . . . . . . . . . . . . .   4
   8.  DNS client behavior . . . . . . . . . . . . . . . . . . . . .   5
   9.  Security considerations . . . . . . . . . . . . . . . . . . .   5
   10. IANA considerations . . . . . . . . . . . . . . . . . . . . .   5
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     12.1.  Normative references . . . . . . . . . . . . . . . . . .   6
     12.2.  Informative references . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Some DNS nameservers return forged answers with different IP
   addresses when they filter, block, or censor access to an internet
   domain name.  A service is typically setup to run at the forged
   address and return information about the filtering that was
   performed.

   This practice causes transport security-related errors at clients,
   such as the case where a HTTPS server serving at the forged answer's
   address does not have a valid TLS certificate configured for the
   domain name.  A security error about a certificate mismatch is
   displayed by the web browser.

   This draft introduces EDNS options [RFC6891] for nameservers to
   provide more information to clients about the filtering as part of
   the DNS response itself, making the need to return forged answers
   unnecessary when domain names are filtered.  By using these options
   instead of forged answers, security errors due to forged answers may
   be avoided at clients, and the information provided in these new EDNS
   options may be used to diagnose filtering or contact administrators
   of the DNS nameservers that performed filtering.

2.  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
   [RFC2119] [RFC8174] when, and only when, they appear in all capitals,
   as shown here.



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3.  EDE-EXTRA-TEXT-LANGUAGE EDNS option

   This option specifies the language that is used in the EXTRA-TEXT
   field of EDNS Extended DNS Error options in the same DNS message.  It
   is not limited to DNS filtering, but may be used in any DNS message
   that contains EDNS Extended DNS Error options.  There MAY be zero or
   one EDE-EXTRA-TEXT-LANGUAGE EDNS option in a message.

   If a human-readable message is generated in the EXTRA-TEXT field of
   EDNS Extended DNS Error options, the nameserver MAY also include an
   EDE-EXTRA-TEXT-LANGUAGE EDNS option in the response.  If the EDE-
   EXTRA-TEXT-LANGUAGE EDNS option is included, the language in its
   option data MUST match the language used in the EXTRA-TEXT field of
   the EDNS Extended DNS Error option.

   The EDNS OPTION-CODE of EDE-EXTRA-TEXT-LANGUAGE is provided in
   Section 10.  The OPTION-DATA MUST contain a language tag as described
   in [RFC5646].

4.  FILTERING-CONTACT EDNS option

   When DNS queries cause filtering to be performed by nameservers and
   negative responses to be returned due to it, the nameserver MAY
   return zero or more FILTERING-CONTACT EDNS options in responses,
   containing contact information of the party that performed the
   filtering.

   DNS nameservers MAY generate these options as described in Section 7.
   DNS clients MAY use the information in these options as described in
   Section 8.

   The EDNS OPTION-CODE of FILTERING-CONTACT is provided in Section 10.
   The OPTION-DATA is a UTF-8 encoded string (that is not nul-
   terminated) containing a contact URI using a contact URI scheme
   listed in TBD: add a link to the contact URI scheme registry.

5.  FILTERING-ORGANIZATION EDNS option

   When DNS queries cause filtering to be performed by nameservers and
   negative responses to be returned due to it, the nameserver MAY
   return zero or one FILTERING-ORGANIZATION EDNS option in responses,
   containing the name of the organization that performed the filtering.

   DNS nameservers MAY generate this option as described in Section 7.
   DNS clients MAY use the information in this option as described in
   Section 8.





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   The EDNS OPTION-CODE of FILTERING-ORGANIZATION is provided in
   Section 10.  The OPTION-DATA is a UTF-8 encoded string (that is not
   nul-terminated) containing the name of the organization that
   performed the filtering.  The language used must match that specified
   in the EDE-EXTRA-TEXT-LANGUAGE EDNS option if the latter option is
   also included.

6.  FILTERING-DB EDNS option

   When DNS queries cause filtering to be performed by nameservers and
   negative responses to be returned due to it, the nameserver MAY
   return zero or one FILTERING-DB EDNS option in responses, containing
   the identifier, name, or description of the filtering database
   against which a matched query caused the filtering to occur.

   DNS nameservers MAY generate this option as described in Section 7.
   DNS clients MAY use the information in this option as described in
   Section 8.

   The EDNS OPTION-CODE of FILTERING-DB is provided in Section 10.  The
   OPTION-DATA is a UTF-8 encoded string (that is not nul-terminated)
   containing the identifier, name, or description of the filtering
   database against which a matched query caused the filtering to occur.

7.  DNS nameserver behavior

   When DNS nameservers filter/block/censor queries to domain names, it
   is RECOMMENDED that they do not return forged positive answers (e.g.,
   containing a different IP address) to filtered queries, but instead
   return negative responses (NODATA or NXDOMAIN) containing an EDNS
   Extended DNS Error option [RFC8914] with corresponding INFO-CODE
   accurately indicating the kind of filtering that was performed.

   When such negative reponses are returned as a result of DNS
   filtering, DNS nameservers MAY include in DNS responses zero or more
   FILTERING-CONTACT EDNS options, and a FILTERING-ORGANIZATION EDNS
   option to provide information about the party that performed the
   filtering.

   The nameserver MAY return a human-readable message describing the
   filtering action that was performed in the EXTRA-TEXT field of the
   EDNS Extended DNS Error option.  If a human-readable message is
   generated in the EXTRA-TEXT field, the nameserver MAY also include an
   EDE-EXTRA-TEXT-LANGUAGE EDNS option in the response.







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8.  DNS client behavior

   DNS clients do not have to specify anything in their queries to
   nameservers to receive DNS filtering-related information.
   Nameservers would automatically return DNS filtering-related
   information in EDNS responses if they are setup to do so.

   When clients query DNS nameservers, they may receive DNS filtering-
   related information as part of the nameserver's responses.  This
   information may be contained in the EDNS options described in this
   draft, as well as EDNS Extended DNS Error option fields (INFO-CODE
   and EXTRA-TEXT) [RFC8914].

   It is strongly RECOMMENDED that clients use DNS transport security
   protocols to query Privacy-enabling DNS servers as defined in
   [RFC9499] to protect the authenticity and integrity during transport
   of the DNS answer as well as the DNS filtering-related information
   that may be contained in it.

   DNS clients may receive zero or more FILTERING-CONTACT EDNS options
   in reponses.  DNS clients MAY make use of the information in these
   options as they would like to.  An example may be to display the
   contact information in a dialog message with hyperlinks, so that
   users may contact filtering parties.

   DNS clients may receive zero or more FILTERING-ORGANIZATION EDNS
   options in reponses.  DNS clients MAY make use of the information in
   the first such EDNS option in the OPT RR as they would like to, and
   ignore any other FILTERING-ORGANIZATION options.  An example may be
   to display the contact information in a dialog message with
   hyperlinks, so that users may contact filtering parties.

9.  Security considerations

   It is strongly RECOMMENDED that clients use DNS transport security
   protocols to query Privacy-enabling DNS servers as defined in
   [RFC9499] to protect the authenticity and integrity during transport
   of the DNS answer as well as the DNS filtering-related information
   that may be contained in it.

   TBD: Any other details that the dnsop WG and authors of draft-ietf-
   dnsop-structured-dns-error want to include.

10.  IANA considerations

   IANA is requested to allocate the following code points in the "DNS
   EDNS0 Option Codes (OPT)" registry in the "Domain Name System (DNS)
   Parameters" registry group.



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      +=======+=========================+==========+================+
      | Value | Name                    | Status   | Reference      |
      +=======+=========================+==========+================+
      | TBD   | EDE-EXTRA-TEXT-LANGUAGE | Optional | See Section 3. |
      +-------+-------------------------+----------+----------------+
      | TBD   | FILTERING-CONTACT       | Optional | See Section 4. |
      +-------+-------------------------+----------+----------------+
      | TBD   | FILTERING-ORGANIZATION  | Optional | See Section 5. |
      +-------+-------------------------+----------+----------------+
      | TBD   | FILTERING-DB            | Optional | See Section 6. |
      +-------+-------------------------+----------+----------------+

                                  Table 1

11.  Acknowledgements

   The FILTERING-CONTACT, FILTERING-ORGANIZATION, and EDE-EXTRA-TEXT-
   LANGUAGE EDNS options are based on the "c", "o", and "l" JSON fields
   respectively as listed in Section 4 (I-JSON in EXTRA-TEXT Field) of
   [I-D.ietf-dnsop-structured-dns-error].

12.  References

12.1.  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>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <https://www.rfc-editor.org/info/rfc5646>.

   [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>.

   [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/info/rfc8914>.




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   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/info/rfc9499>.

12.2.  Informative references

   [I-D.ietf-dnsop-structured-dns-error]
              Wing, D., Reddy.K, T., Cook, N., and M. Boucadair,
              "Structured Error Data for Filtered DNS", Work in
              Progress, Internet-Draft, draft-ietf-dnsop-structured-dns-
              error-18, 18 March 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-
              structured-dns-error-18>.

Author's Address

   Mukund Sivaraman
   Banu Systems Private Limited
   6001 Beach Road, #19-09, Golden Mile Tower
   SINGAPORE 199589
   Singapore
   Email: muks@banu.com
   URI:   https://banu.com/




























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