Afnic

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NLnet Labs

Science Park 400 Amsterdam 1098 XH NL willem@nlnetlabs.nl https://nlnetlabs.nl/

Quad9

Werdstrasse 2 Zürich 8004 CH babak@farrokhi.net https://quad9.net/

The FreeBSD Foundation

3980 Broadway St Boulder CO 80304 US bofh@freebsd.org https://freebsdfoundation.org/

General Internet Engineering Task Force DNS DNSSEC optimization caching 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.

Introduction When an organisation operates a big network of DNS resolvers , for instance for an important public resolver (), 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!

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 when, and only when, they appear in all capitals, as shown here.

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

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 . 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? 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 ? 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.

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

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.

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.

Related and future work

Related work describes a mechanism to fill DNS caches with data. The format is, like in this document, standard DNS as seen on the wire.

Future work

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 and/or to synthetize negative answers since it did not validate data itself?

Transport of messages It may be interesting to replace the unicast messages by multicast (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 which is well suited for publish-by-one/consume-by-many? What about protocols like protocol buffers? TODO What about dnstap?

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

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.

References Normative References Informative References OASIS

Acknowledgements Original idea at the RIPE hackathon in march 2025 at the Netnod office in Stockholm.