Network Working Group F. Obser Internet-Draft OpenBSD Intended status: Informational 21 October 2024 Expires: 24 April 2025 DNS Resolver Information Key for DNS64 draft-fobser-resinfo-dns64-00 Abstract This document specifies a DNS Resolver Information Key/Value pair to inform DNS clients of the presence of DNS64. 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 24 April 2025. Copyright Notice Copyright (c) 2024 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 and restrictions with respect to this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 2 2. Relation to RFC 7050 . . . . . . . . . . . . . . . . . . . . 2 3. dns64 Resolver Information Key/Value . . . . . . . . . . . . 3 Obser Expires 24 April 2025 [Page 1] Internet-Draft Resinfo DNS64 October 2024 3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction DNS64 [RFC6147] performed by a DNS resolver together with NAT64 [RFC6146] allows an IPv6-only client to initiate communications by name to an IPv4-only server. To achieve this, the DNS resolver synthesizes AAAA records from A records. However, this breaks DNSSEC [RFC4033] [RFC4034] [RFC4035] validation for DNS clients of the resolver if they perform their own validation. [RFC6147] Section 3 discusses this in detail. In general, a validating DNS client has to be aware that a resolver is performing DNS64. [RFC9606] specifies a DNS resource record (RR) type RESINFO to allow resolvers to publish information about their capabilities and policies. This can be used to inform DNS clients that DNS64 is performed by the DNS resolver. 1.1. 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Relation to RFC 7050 [RFC7050] describes a heuristic to learn the IPv6 prefix used by a NAT64 gateway. Nodes can use this information to perform local address synthesis, for example using 464XLAT [RFC6877]. This has security implications, making [RFC7050] difficult to deploy. A modern mechanism, like PREF64 [RFC8781] is easier to deploy, leading to a desire to deprecate [RFC7050] entirely. A validating DNS client on the other hand still needs to know about the presence of DNS64 on the DNS resolver it uses, as noted in the introduction. Using the [RFC9606] RESINFO mechanism and not using the learned information for address synthesis avoids the security problems of [RFC7050]. Obser Expires 24 April 2025 [Page 2] Internet-Draft Resinfo DNS64 October 2024 3. dns64 Resolver Information Key/Value dns64: The presence of this key indicates that the DNS resolver performs address synthesis. Note that, per the rules for the keys defined in Section 6.4 of [RFC6763], if there is no '=' in a key, then it is a boolean attribute, simply identified as being present, with no value. The DNS resolver MAY return an IPv6 prefix or a comma separated list of prefixes to indicate not just that DNS64 is being performed but also to let the client know which prefix or prefixes are in use. The prefixes MUST be represented using the canonical representation format of [RFC5952]. 3.1. Examples DNS64 address synthesis is performed by the DNS resolver. No information about the used prefix is given. resolver.example.net. 7200 IN RESINFO dns64 DNS64 address synthesis is performed. The [RFC6052] Well-Known Prefix 64:ff9b::/96 is used. resolver.example.net. 7200 IN RESINFO dns64=64:ff9b::/96 DNS64 address synthesis is performed. The [RFC6052] Well-Known Prefix 64:ff9b::/96 and the Network-Specific Prefix 2001:db8:64::/56 are used. resolver.example.net. 7200 IN RESINFO dns64=64:ff9b::/96,2001:db8:64::/56 4. Security Considerations The security considerations of [RFC9606] apply. 5. IANA Considerations The IANA is requested to add the key "dns64", with the description of "The presence of the key indicates that DNS64 address synthesis is performed", and a reference to this document. Obser Expires 24 April 2025 [Page 3] Internet-Draft Resinfo DNS64 October 2024 +=======+========================================+===============+ | Name | Description | Reference | +=======+========================================+===============+ | dns64 | The presence of the key indicates that | RFC EDITOR: | | | DNS64 address synthesis is performed. | THIS DOCUMENT | +-------+----------------------------------------+---------------+ Table 1 6. References 6.1. 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, . [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, DOI 10.17487/RFC5952, August 2010, . [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9606] Reddy.K, T. and M. Boucadair, "DNS Resolver Information", RFC 9606, DOI 10.17487/RFC9606, June 2024, . 6.2. Informative References [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, DOI 10.17487/RFC4033, March 2005, . [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005, . Obser Expires 24 April 2025 [Page 4] Internet-Draft Resinfo DNS64 October 2024 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, . [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, DOI 10.17487/RFC6052, October 2010, . [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011, . [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van Beijnum, "DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to IPv4 Servers", RFC 6147, DOI 10.17487/RFC6147, April 2011, . [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: Combination of Stateful and Stateless Translation", RFC 6877, DOI 10.17487/RFC6877, April 2013, . [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis", RFC 7050, DOI 10.17487/RFC7050, November 2013, . [RFC8781] Colitti, L. and J. Linkova, "Discovering PREF64 in Router Advertisements", RFC 8781, DOI 10.17487/RFC8781, April 2020, . Author's Address Florian Obser OpenBSD Email: florian+ietf@narrans.de Obser Expires 24 April 2025 [Page 5]