Synchronizing caches of DNS resolvers
draft-bortzmeyer-dnsop-poisonlicious-02

DNSOP Working Group                                        S. Bortzmeyer
Internet-Draft                                                     Afnic
Intended status: Experimental                                  W. Toorop
Expires: 11 July 2026                                         NLnet Labs
                                                             B. Farrokhi
                                                                   Quad9
                                                               M. Rahman
                                                  The FreeBSD Foundation
                                                                 O. Surý
                                             Internet Systems Consortium
                                                             O. Moerbeek
                                                                PowerDNS
                                                          7 January 2026

                 Synchronizing caches of DNS resolvers
                draft-bortzmeyer-dnsop-poisonlicious-02

Abstract

   Network of cooperating and mutually trusting DNS resolvers could
   benefit from cache sharing, where one resolver would distribute the
   result of a resolution to other resolvers.  This document
   standardizes a protocol to do so.

About This Document

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

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-bortzmeyer-dnsop-
   poisonlicious/.

   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/https://github.com/DNS-Hackathon/Poisonlicious.

Status of This Memo

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  The protocol  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   5
   7.  Related and future work . . . . . . . . . . . . . . . . . . .   5
     7.1.  Related work  . . . . . . . . . . . . . . . . . . . . . .   5
     7.2.  Future work . . . . . . . . . . . . . . . . . . . . . . .   5
       7.2.1.  Negative answers  . . . . . . . . . . . . . . . . . .   5
       7.2.2.  Transport of messages . . . . . . . . . . . . . . . .   5
       7.2.3.  Packing of messages . . . . . . . . . . . . . . . . .   6
       7.2.4.  Different responses . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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1.  Introduction

   When an organisation operates a big network of DNS resolvers
   [RFC1034] [RFC1035], for instance for an important public resolver
   Section 6 of [RFC9499], it may be a performance improvement to
   distribute the result of the resolution process between the
   resolvers.  This document standardizes how to to do so, using
   blockchains (just kidding) and unicast messages to a set of pre-
   configured peers.

   TODO data from Quad9 to show that there is a caching improvement to
   expect.  Measuring the efficiency of caching optimizations is hard!

1.1.  Requirements Language

   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.

1.2.  Terminology

   Network of resolvers (TODO or resolver set?  Or resolver
   cluster?):
      A set of resolvers working together under the same administration

   Peer (or peer resolver):
      One of the other resolvers in the network

   Originating resolver:
      A resolver sending data to its peers in the network

   Receiving resolver (or receiving peer):
      A resolver receiving data from one of its peers in the network

   Resolver:
      As used in Section 6 of [RFC9499]

2.  The protocol

   When completing a successful DNS resolution, the resolver transmits a
   DNS message (with the Q/R bit set, since it is a response) to the
   pre-configured peers, authenticating with TSIG [RFC8945].  TODO SIG0?
   DoT?  No acknowledgment is sent or expected.  To save work, the
   resolver MAY send the data only if the TTL is higher than some
   predefined value.

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   The resolver must send only data that it is sure of (for instance by
   DNSSEC validation or because it came with the AA bit from the queried
   server).  Since all of the network of resolvers are in the same
   organizational domain, they MUST agree on the same policy for this
   assessment.

   Messages of this protocol are distinguished from other DNS messages
   by the TSIG key they use (which must therefore be specific to this
   protocol).  TODO or by a dedicated port?

   This message MAY be the message received by the resolver from the
   authoritative name servers or it MAY be a new message with data
   composed from data already obtained by the resolver.  TODO privacy
   risks when sending the question section?  (See Section 5

   The EDNS section MUST be a new one, created to fit the needs of
   successful transmission to the peer.  TODO what about ECS [RFC7871]

   Each peer then MAY store the data in its cache.  The peer is not
   supposed to do DNSSEC validation (there is not always all the
   necessary data in the message).  TODO cache only what is in the
   Answer section?  See above about assessing the trustiness of the
   data.  TODO Section 5.4.1 of [RFC2181] talks about the ranking of
   data.  Should we describe it?  Since it is supposed to be used inside
   an organisation, where all peers trust each other, and have a
   consistent policy, is it necessary?  The idea is that the data is as
   trustworthy as if you validated it yourself.

3.  IANA Considerations

   None.  [RFC-Editor: you may delete this section]

4.  Security Considerations

   The integrity and authenticity of the cached data is of course
   critical.  DNSSEC would help but it is not yet universally deployed
   and, moreover, the peer resolvers should not have to redo the
   validation.  So, trust between the peer resolvers is expected because
   it is the only way for the receiver to be sure of the data.  One way
   to do so is to have all of the peers under the same organisational
   authority, as mandated here.

   For the same reason, the channel between peers must be protected,
   preferrably with cryptography (currently, TSIG is mandatory).  ACL
   and other network techniques are of course useful.

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   Encryption is less important than authentication since we transmit
   only public data.  Nevertheless, it is better to be sure that the
   channel between the peers is not open to snooping.

5.  Privacy Considerations

   Confidentiality is currently out of scope for this document.  The
   communication between the originating resolver and its receiving
   peers could be encrypted, for instance with DoT but it is not
   otherwise specified.

   If the originating resolver sends the original question section in
   its messages to receiving peers, it can have bad privacy consequences
   [RFC9076] TODO: delete this section?  Replace it with dummy data?

6.  Operational Considerations

   It is reminded that all resolvers in the network need to trust each
   other, probably being in the same administrative domain.  This
   specification is not meant to be deployed between unrelated
   resolvers.

   The netwok of peer resolvers have to be configured out-of-band
   before.  The way to do it is out-of-scope for this specification.

7.  Related and future work

7.1.  Related work

   [I-D.hl-dnsop-cache-filling] describes a mechanism to fill DNS caches
   with data.  The format is, like in this document, standard DNS as
   seen on the wire.

7.2.  Future work

7.2.1.  Negative answers

   TODO What to do about them?  Transmit them?  (Be careful of the risk
   of overloading receving peers for instance when there is a dictionary
   attack.)  Can a receiving peer use [RFC8020] and/or [RFC8198] to
   synthetize negative answers since it did not validate data itself?

7.2.2.  Transport of messages

   Messages could be transmitted in long-lived TCP sessions, too.

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   If there are 1,000 servers, sending 1,000 messages, or having a full
   mesh of 1,000 TCP connections may be too much.  It may be interesting
   to replace the unicast messages by multicast [RFC5110] (the issues of
   multicast on the public Internet do no apply here since we envision
   work under only one organisation).

   Is the use of a DHT reasonable?

   Why not MQTT [MQTT] which is well suited for publish-by-one/consume-
   by-many?  What about protocols like protocol buffers?  TODO What
   about dnstap?

7.2.3.  Packing of messages

   It could be interesting to optimize by packing the data in a C-DNS
   [RFC8618] flow, sent with TCP (with TLS) or QUIC.  (Of course, other
   formats/protocols are possible.)

7.2.4.  Different responses

   When the authoritative servers send different replies depending on
   the client, the various peers may send different (and under-
   optimized) responses to a receiving peer.

8.  References

8.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/rfc/rfc1034>.

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

   [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>.

   [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>.

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   [RFC8945]  Dupont, F., Morris, S., Vixie, P., Eastlake 3rd, D.,
              Gudmundsson, O., and B. Wellington, "Secret Key
              Transaction Authentication for DNS (TSIG)", STD 93,
              RFC 8945, DOI 10.17487/RFC8945, November 2020,
              <https://www.rfc-editor.org/rfc/rfc8945>.

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

8.2.  Informative References

   [I-D.hl-dnsop-cache-filling]
              Hoffman, P. E. and M. Larson, "Additional Method for
              Filling DNS Caches", Work in Progress, Internet-Draft,
              draft-hl-dnsop-cache-filling-00, 2 March 2018,
              <https://datatracker.ietf.org/doc/html/draft-hl-dnsop-
              cache-filling-00>.

   [MQTT]     OASISi, "MQTT Version 5.0", 2019, <https://docs.oasis-
              open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.docx>.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
              <https://www.rfc-editor.org/rfc/rfc2181>.

   [RFC5110]  Savola, P., "Overview of the Internet Multicast Routing
              Architecture", RFC 5110, DOI 10.17487/RFC5110, January
              2008, <https://www.rfc-editor.org/rfc/rfc5110>.

   [RFC7871]  Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", RFC 7871,
              DOI 10.17487/RFC7871, May 2016,
              <https://www.rfc-editor.org/rfc/rfc7871>.

   [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/rfc/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/rfc/rfc8198>.

   [RFC8618]  Dickinson, J., Hague, J., Dickinson, S., Manderson, T.,
              and J. Bond, "Compacted-DNS (C-DNS): A Format for DNS
              Packet Capture", RFC 8618, DOI 10.17487/RFC8618, September
              2019, <https://www.rfc-editor.org/rfc/rfc8618>.

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   [RFC9076]  Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076,
              DOI 10.17487/RFC9076, July 2021,
              <https://www.rfc-editor.org/rfc/rfc9076>.

Appendix A.  Acknowledgements

   Original idea at the DNS hackathon (RIPE-NCC / Netnod / DNS-OARC) in
   March 2025 at the Netnod office in Stockholm.

Authors' Addresses

   Stéphane Bortzmeyer
   Afnic
   7 avenue du 8 mai 1945
   78280 Guyancourt
   France
   Email: bortzmeyer+ietf@nic.fr
   URI:   https://www.afnic.fr/

   Willem Toorop
   NLnet Labs
   Science Park 400
   1098 XH Amsterdam
   Netherlands
   Email: willem@nlnetlabs.nl
   URI:   https://nlnetlabs.nl/

   Babak Farrokhi
   Quad9
   Werdstrasse 2
   CH-8004 Zürich
   Switzerland
   Email: babak@farrokhi.net
   URI:   https://quad9.net/

   Moin Rahman
   The FreeBSD Foundation
   3980 Broadway St
   Boulder,  CO 80304
   United States of America
   Email: bofh@freebsd.org
   URI:   https://freebsdfoundation.org/

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   Ondřej Surý
   Internet Systems Consortium
   Czechia
   Email: ondrej@isc.org

   Otto Moerbeek
   PowerDNS
   Netherlands
   Email: otto.moerbeek@powerdns.com

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