Internet Engineering Task Force S. Bortzmeyer Internet-Draft Afnic Intended status: Experimental W. Toorop Expires: 24 September 2025 NLnet Labs B. Farrokhi Quad9 M. Rahman The FreeBSD Foundation 23 March 2025 Synchronizing caches of DNS resolvers draft-bortzmeyer-dnsop-poisonlicious-00 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. 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/. 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Expires 24 September 2025 [Page 1] Internet-Draft Poisonlicious March 2025 extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. The protocol . . . . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Operational Considerations . . . . . . . . . . . . . . . . . 4 6. Related and future work . . . . . . . . . . . . . . . . . . . 4 6.1. Related work . . . . . . . . . . . . . . . . . . . . . . 4 6.2. Future work . . . . . . . . . . . . . . . . . . . . . . . 5 6.2.1. Negative answers . . . . . . . . . . . . . . . . . . 5 6.2.2. Transport of messages . . . . . . . . . . . . . . . . 5 6.2.3. Packing of messages . . . . . . . . . . . . . . . . . 5 6.2.4. Different responses . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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 improvment 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 improvment 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. Bortzmeyer, et al. Expires 24 September 2025 [Page 2] Internet-Draft Poisonlicious March 2025 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. 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? [RFC9076] Force its elision? 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 Bortzmeyer, et al. Expires 24 September 2025 [Page 3] Internet-Draft Poisonlicious March 2025 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. 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. 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. 6. Related and future work 6.1. 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. Bortzmeyer, et al. Expires 24 September 2025 [Page 4] Internet-Draft Poisonlicious March 2025 6.2. Future work 6.2.1. 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? 6.2.2. Transport of messages 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). For instance, if we use DoT for the transport of messages and if there are 1,000 servers, having a full mesh of DoT connections may be too much. 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? 6.2.3. 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.) 6.2.4. 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. 7. References 7.1. Normative References [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, . [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . Bortzmeyer, et al. Expires 24 September 2025 [Page 5] Internet-Draft Poisonlicious March 2025 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219, RFC 9499, DOI 10.17487/RFC9499, March 2024, . 7.2. Informative References [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, . [RFC5110] Savola, P., "Overview of the Internet Multicast Routing Architecture", RFC 5110, DOI 10.17487/RFC5110, January 2008, . [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, . [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, November 2016, . [RFC8198] Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198, July 2017, . [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, . Bortzmeyer, et al. Expires 24 September 2025 [Page 6] Internet-Draft Poisonlicious March 2025 [RFC9076] Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076, DOI 10.17487/RFC9076, July 2021, . [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, . [MQTT] OASIS, "MQTT Version 5.0", 2019, . 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/ Bortzmeyer, et al. Expires 24 September 2025 [Page 7] Internet-Draft Poisonlicious March 2025 Moin Rahman The FreeBSD Foundation 3980 Broadway St Boulder, CO 80304 United States of America Email: bofh@freebsd.org URI: https://freebsdfoundation.org/ Bortzmeyer, et al. Expires 24 September 2025 [Page 8]