DNS Delegation P. Homburg Internet-Draft NLnet Labs Intended status: Standards Track T. Wicinski Expires: 4 September 2025 Cox Communications J. V. Zutphen University of Amsterdam W. Toorop NLnet Labs 3 March 2025 Incrementally Deployable Extensible Delegation for DNS draft-homburg-deleg-incremental-deleg-03 Abstract This document proposes a mechanism for extensible delegations in the DNS. The mechanism realizes delegations with resource record sets placed below a _deleg label in the apex of the delegating zone. This authoritative delegation point can be aliased to other names using CNAME and DNAME. This document proposes a new DNS resource record type, IDELEG, which is based on the SVCB and inherits extensibility from it. Support in recursive resolvers suffices for the mechanism to be fully functional. The number of subsequent interactions between the recursive resolver and the authoritative name servers is comparable with those for DNS Query Name Minimisation. Additionally, but not required, support in the authoritative name servers enables optimized behavior with reduced (simultaneous) queries. None, mixed or full deployment of the mechanism on authoritative name servers are all fully functional, allowing for the mechanism to be incrementally deployed. 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-homburg-deleg-incremental- deleg/. Discussion of this document takes place on the deleg Working Group mailing list (mailto:dd@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/dd/. Subscribe at https://www.ietf.org/mailman/listinfo/dd/. Homburg, et al. Expires 4 September 2025 [Page 1] Internet-Draft incremental-deleg March 2025 Source for this draft and an issue tracker can be found at https://github.com/NLnetLabs/incremental-deleg. 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 4 September 2025. Copyright Notice Copyright (c) 2025 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. Code Components 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Signaling capabilities of the authoritative name servers . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. _Note to the RFC Editor_: please remove this subsection before publication. . . . . . . . . . . . . . . . . . . . 4 1.3. Outsourcing operation of the delegation . . . . . . . . . 4 1.4. DNSSEC protection of the delegation . . . . . . . . . . . 4 1.5. Maximize ease of deployment . . . . . . . . . . . . . . . 5 1.6. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 2. The IDELEG resource record type . . . . . . . . . . . . . . . 7 3. Delegation administration . . . . . . . . . . . . . . . . . . 8 3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 Homburg, et al. Expires 4 September 2025 [Page 2] Internet-Draft incremental-deleg March 2025 3.1.1. One name server within the subzone . . . . . . . . . 8 3.1.2. Two name servers within the subzone . . . . . . . . . 8 3.1.3. Outsourced to an operator . . . . . . . . . . . . . . 9 3.1.4. DNSSEC signed name servers within the subzone . . . . 9 4. Minimal implementation . . . . . . . . . . . . . . . . . . . 11 4.1. Recursive Resolver behavior . . . . . . . . . . . . . . . 11 4.2. _deleg label presence . . . . . . . . . . . . . . . . . . 13 5. Optimized implementation . . . . . . . . . . . . . . . . . . 14 5.1. Authoritative name server support . . . . . . . . . . . . 15 5.2. Resolver behavior with authoritative name server support . . . . . . . . . . . . . . . . . . . . . . . . . 18 6. Extra optimized implementation . . . . . . . . . . . . . . . 19 7. Priming queries . . . . . . . . . . . . . . . . . . . . . . . 20 8. How does incremental deleg meet the requirements . . . . . . 20 9. Comparison with other delegation mechanisms . . . . . . . . . 22 9.1. Comparison with legacy delegations . . . . . . . . . . . 24 9.1.1. The delegation point . . . . . . . . . . . . . . . . 24 9.1.2. Legacy referrals . . . . . . . . . . . . . . . . . . 24 9.1.3. Number of queries . . . . . . . . . . . . . . . . . . 25 9.2. Comparison with Name DNS Query Name Minimisation . . . . 25 9.3. Comparison with I-D.wesplaap-deleg . . . . . . . . . . . 25 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 26 11. Security Considerations . . . . . . . . . . . . . . . . . . . 27 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 12.1. IDELEG RR type . . . . . . . . . . . . . . . . . . . . . 27 12.2. _deleg Node Name . . . . . . . . . . . . . . . . . . . . 27 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 13.1. Normative References . . . . . . . . . . . . . . . . . . 28 13.2. Informative References . . . . . . . . . . . . . . . . . 29 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 1. Introduction This document describes a delegation mechanism for the Domain Name System (DNS) [STD13] that addresses several matters that, at the time of writing, are suboptimally supported or not supported at all. These matters are elaborated upon in sections 1.1, 1.3 and 1.4. In addition, the mechanism described in this document aspires to be maximally deployable, which is elaborated upon in Section 1.5. Homburg, et al. Expires 4 September 2025 [Page 3] Internet-Draft incremental-deleg March 2025 1.1. Signaling capabilities of the authoritative name servers A new IDELEG resource record (RR) type is introduced in this document, which is based on and inherits the wire and presentation format from SVCB [RFC9460]. All Service Binding Mappings, as well as the capability signalling, that are specified in [RFC9461] are also applicable to IDELEG, with the exception of the limitations on AliasMode records in Section 6 of [RFC9460]. Capability signalling of DNS over Transport Layer Protocol [RFC7858] (DoT), DNS Queries over HTTPS [RFC8484] and DNS over Dedicated QUIC Connections [RFC9250], on default or alternative ports, can all be used as specified in [RFC9461]. The IDELEG RR type inherits its extensibility from the SVCB RR type, which is designed to be extensible to support future uses (such as keys for encrypting the TLS ClientHello [I-D.ietf-tls-esni].) 1.2. _Note to the RFC Editor_: please remove this subsection before publication. The name IDELEG is chosen to avoid confusion with [I-D.wesplaap-deleg]. 1.3. Outsourcing operation of the delegation Delegation information is stored at an authoritative location in the zone with this mechanism. Legacy methods to redirect this information to another location, possible under the control of another operator, such as (CNAME Section 3.6.2 of [RFC1034]) and DNAME [RFC6672] remain functional. One could even outsource all delegation operational practice to another party with an DNAME on the _deleg label on the apex of the delegating zone. Additional to the legacy methods, a delegation may be outsourced to a third parties by having RRs in AliasMode. Unlike SVCB, IDELEG allows for more than a single IDELEG RR in AliasMode in a IDELEG RRset, enabling outsourcing a delegation to multiple different operators. 1.4. DNSSEC protection of the delegation With legacy delegations, the NS RRset at the parent side of a delegation as well as glue records for the names in the NS RRset are not authoritative and not DNSSEC signed. An adversary that is able to spoof a referral response, can alter this information and redirect all traffic for the delegation to a rogue name server undetected. The adversary can then perceive all queries for the redirected zone (Privacy concern) and alter all unsigned parts of responses (such as further referrals, which is a Security concern). Homburg, et al. Expires 4 September 2025 [Page 4] Internet-Draft incremental-deleg March 2025 DNSSEC protection of delegation information prevents that, and is the only countermeasure that also works against on-path attackers. At the time of writing, the only way to DNSSEC validate and verify delegations at all levels in the DNS hierarchy is to revalidate delegations [I-D.ietf-dnsop-ns-revalidation], which is done after the fact and has other security concerns (Section 7 of [I-D.ietf-dnsop-ns-revalidation]). Direct delegation information (provided by IDELEG RRs in ServiceMode) includes the hostnames of the authoritative name servers for the delegation as well as IP addresses for those hostnames. Since the information is stored authoritatively in the delegating zone, it will be DNSSEC signed if the zone is signed. When the delegation is outsourced, then it's protected when the zones providing the aliasing resource records _and_ the zones serving the targets of the aliases are all DNSSEC signed. 1.5. Maximize ease of deployment Delegation information is stored authoritatively within the delegation zone. No semantic changes as to what zones are authoritative for what data are needed. As a consequence, existing DNS software, such as authoritative name servers and DNSSEC signing software, can remain unmodified. Unmodified authoritative name server software will serve the delegation information when queried for. Unmodified signers will sign the delegation information in the delegating zone. Only the recursive resolver needs modification to follow referrals as provided by the delegation information. Such a resolver would explicitly query for the delegations administered as specified in Section 3. The number of round trips from the recursive resolver to the authoritative name server is comparable to what is needed for DNS Query Name Minimisation [RFC9156]. Additional implementation in the authoritative name server optimizes resolution and reduces the number of simultaneous in parallel queries to that what would be needed for legacy delegations. None, mixed or full deployment of the mechanism on authoritative name servers are all fully functional, allowing for the mechanism to be incrementally deployed on the authoritative name servers. Implementation in the recursive may be less demanding with respect to (among other things) DNSSEC validation because there is no need to make additional exceptions as to what is authoritative at the parent side of a delegation. Homburg, et al. Expires 4 September 2025 [Page 5] Internet-Draft incremental-deleg March 2025 1.6. Terminology 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. This document follows terminology as defined in [BCP219]. Throughout this document we will also use terminology with the meaning as defined below: Incremental deleg: The delegation mechanism as specified in this document. Incremental delegation: A delegation as specified in this document Legacy delegations: The way delegations are done in the DNS traditionally as defined in [STD13]. Delegating zone: The zone in which the delegation is administered. Sometimes also called the "parent zone" of a delegation. Subzone: The zone that is delegated to from the delegating zone. Delegating name: The name which realizes the delegation. In legacy delegations, this name is the same as the name of the subzone to which the delegation refers. Delegations described in this document are provided with a different name than the zone that is delegated to. Delegation point: The location in the delegating zone where the RRs are provided that make up the delegation. In legacy delegations, this is the parent side of the zone cut and has the same name as the subzone. With incremental deleg, this is the location given by the delegating name. Triggering query: The query on which resolution a recursive resolver is working. Target zone: Homburg, et al. Expires 4 September 2025 [Page 6] Internet-Draft incremental-deleg March 2025 The zone for which the authoritative servers, that a resolver contacts while iterating, are authoritative. 2. The IDELEG resource record type The IDELEG RR type is a variant of SVCB [RFC9460] for use with resolvers to perform iterative resolution (Section 5.3.3 of [RFC1034]). The IDELEG type requires registration in the "Resource Record (RR) TYPEs" registry under the "Domain Name System (DNS) Parameters" registry group (see IDELEG RR type (Section 12.1)). The protocol-specific mapping specification for iterative resolutions are the same as those for "DNS Servers" [RFC9461]. Section 2.4.2 of [RFC9460] states that SVCB RRsets SHOULD only have a single RR in AliasMode, and that if multiple AliasMode RRs are present, clients or recursive resolvers SHOULD pick one at random. Different from SVCB (Section 2.4.2 of [RFC9460]), IDELEG allows for multiple AliasMode RRs to be present in a single IDELEG RRset. Note however that the target of a IDELEG RR in AliasMode is a SVCB RRset for the "dns" service type adhering fully to the Service Binding Mapping for DNS Servers as specified in [RFC9461]. Section 2.4.1 of [RFC9460] states that within an SVCB RRset, all RRs SHOULD have the same mode, and that if an RRset contains a record in AliasMode, the recipient MUST ignore any ServiceMode records in the set. Different from SVCB, mixed ServiceMode and AliasMode RRs are allowed in a IDELEG RRset. When an mixed ServiceMode and AliasMode IDELEG RRset is encountered by a resolver, the resolver first picks one of the AliasMode RRs or all ServiceMode RRs, giving all ServiceMode RRs equal weight as each single AliasMode RR. When the result of that choice is an AliasMode RR, then that RR is followed and the resulting IDELEG RRset is reevaluated. When the result of that choice is all ServiceMode RRs, then within that set the resolver adheres to ServicePriority value. At the delegation point (for example customer._deleg.example.), the host names of the authoritative name servers for the subzone, are given in the TargetName RDATA field of IDELEG records in ServiceMode. Port Prefix Naming Section 3 of [RFC9461] is not used at the delegation point, but MUST be used when resolving the aliased to name servers with IDELEG RRs in AliasMode. Homburg, et al. Expires 4 September 2025 [Page 7] Internet-Draft incremental-deleg March 2025 3. Delegation administration An extensible delegation is realized with a IDELEG Resource Record set (RRset) [RFC9460] below a specially for the purpose reserved label with the name _deleg at the apex of the delegating zone. The _deleg label scopes the interpretation of the IDELEG records and requires registration in the "Underscored and Globally Scoped DNS Node Names" registry (see _deleg Node Name (Section 12.2)). The full scoping of delegations includes the labels that are *below* the _deleg label and those, together with the name of the delegating domain, make up the name of the subzone to which the delegation refers. For example, if the delegating zone is example., then a delegation to subzone customer.example. is realized by a IDELEG RRset at the name customer._deleg.example. in the parent zone. A fully scoped delegating name (such as customer._deleg.example.) is referred to further in this document as the "delegation point". Note that if the delegation is outsourcing to a single operator represented in a single IDELEG RR, it is RECOMMENDED to refer to the name of the operator's IDELEG RRset with a CNAME on the delegation point instead of a IDELEG RR in AliasMode Section 10.2 of [RFC9460]. 3.1. Examples 3.1.1. One name server within the subzone $ORIGIN example. @ IN SOA ns zonemaster ... customer1._deleg IN IDELEG 1 ( ns.customer1 ipv4hint=198.51.100.1,203.0.113.1 ipv6hint=2001:db8:1::1,2001:db8:2::1 ) Figure 1: One name server within the subzone 3.1.2. Two name servers within the subzone $ORIGIN example. @ IN SOA ns zonemaster ... customer2._deleg IN IDELEG 1 ns1.customer2 ( ipv4hint=198.51.100.1 ipv6hint=2001:db8:1::1 ) IN IDELEG 1 ns2.customer2 ( ipv4hint=203.0.113.1 ipv6hint=2001:db8:2::1 ) Figure 2: Two name servers within the subzone Homburg, et al. Expires 4 September 2025 [Page 8] Internet-Draft incremental-deleg March 2025 3.1.3. Outsourced to an operator $ORIGIN example. @ IN SOA ns zonemaster ... customer3._deleg IN CNAME _dns.ns.operator1 Figure 3: Outsourced with CNAME Instead of using CNAME, the outsourcing could also been accomplished with a IDELEG RRset with a single IDELEG RR in AliasMode. The configuration below is operationally equivalent to the CNAME configuration above. It is RECOMMENDED to use a CNAME over a IDELEG RRset with a single IDELEG RR in AliasMode (Section 10.2 of [RFC9460]). Note that a IDELEG RRset refers with TargetName to an DNS service, which will be looked up using Port Prefix Naming Section 3 of [RFC9461], but that CNAME refers to the domain name of the target IDELEG RRset (or CNAME) which may have an _dns prefix. $ORIGIN example. @ IN SOA ns zonemaster ... customer3._deleg IN IDELEG 0 ns.operator1 Figure 4: Outsourced with an AliasMode IDELEG RR The operator IDELEG RRset could for example be: $ORIGIN operator1.example. @ IN SOA ns zonemaster ... _dns.ns IN IDELEG 1 ns ( alpn=h2,dot,h3,doq ipv4hint=192.0.2.1 ipv6hint=2001:db8:3::1 dohpath=/q{?dns} ) IN IDELEG 2 ns ( ipv4hint=192.0.2.2 ipv6hint=2001:db8:3::2 ) ns IN AAAA 2001:db8:3::1 IN AAAA 2001:db8:3::2 IN A 192.0.2.1 IN A 192.0.2.2 Figure 5: Operator zone 3.1.4. DNSSEC signed name servers within the subzone Homburg, et al. Expires 4 September 2025 [Page 9] Internet-Draft incremental-deleg March 2025 $ORIGIN @ IN SOA ns zonemaster ... IN RRSIG SOA ... IN DNSKEY 257 3 15 ... IN RRSIG DNSKEY ... IN NS ns.example. IN NSEC customer5._deleg SOA RRSIG NSEC DNSKEY IN RRSIG NSEC ... customer5._deleg IN IDELEG 1 ns.customer5 alpn=h2,h3 ( ipv4hint=198.51.100.5 ipv6hint=2001:db8:5::1 dohpath=/dns-query{?dns} ) IN RRSIG IDELEG ... IN NSEC customer7._deleg RRSIG NSEC IDELEG IN RRSIG NSEC ... customer7._deleg IN CNAME customer5._deleg IN RRSIG CNAME ... IN NSEC customer5 CNAME RRSIG NSEC IN RRSIG NSEC ... customer5 IN NS ns.customer5 ns.customer5 IN A 198.51.100.5 IN AAAA 2001:db8:5::1 customer5 IN DS 17405 15 2 ... IN RRSIG DS ... IN NSEC customer6 NS DS RRSIG NSEC IN RRSIG NSEC ... customer6 IN NS ns.customer6 ns.customer6 IN A 203.0.113.1 IN AAAA 2001:db8:6::1 customer6 IN DS ... IN RRSIG DS ... IN NSEC customer7 NS DS RRSIG NSEC IN RRSIG NSEC ... customer7 IN NS ns.customer5 IN DS ... IN RRSIG DS ... IN NSEC example. NS DS RRSIG NSEC IN RRSIG NSEC ... Figure 6: DNSSEC signed incremental deleg zone Homburg, et al. Expires 4 September 2025 [Page 10] Internet-Draft incremental-deleg March 2025 customer5.example. is delegated to in an extensible way and customer6.example. is delegated only in a legacy way. customer7.example.'s delegation is outsourced to customer5's delegation. The delegation signals that the authoritative name server supports DoH. customer5.example., customer6.example. and example. are all DNSSEC signed. The DNSSEC authentication chain links from example. to customer5.example. in the for DNSSEC conventional way with the signed customer5.example. DS RRset in the example. zone. Also, customer6.example. is linked to from example. with the signed customer6.example. DS RRset in the example. zone. Note that both customer5.example. and customer6.example. have legacy delegations in the zone as well. It is important to have those legacy delegations to maintain support for legacy resolvers, that do not support incremental deleg. DNSSEC signers SHOULD construct the NS RRset and glue for the legacy delegation from the IDELEG RRset. 4. Minimal implementation Support in recursive resolvers suffices for the mechanism to be fully functional. Section 4.1 specifies the basic algorithm for resolving incremental delegations. In Section 4.2, an optimization is presented that will reduce the number of (parallel) queries especially for when authoritative name server support is still lacking and there are still many zones that do not contain incremental delegations. 4.1. Recursive Resolver behavior If the triggering query name is the same as the name of the target zone apex, then no further delegation will occur, and resolution will complete. No special behavior or processing is needed. Otherwise, the triggering query is below the target zone apex and a delegation may exist in the target zone. In this case two parallel queries MUST be sent. One for the triggering query in the way that is conventional with legacy delegations (which could be just the triggering query or a minimised query [RFC9156]), and one _incremental deleg query_ with query type IDELEG. The incremental deleg query name is constructed by concatenating the first label below the part that the triggering query name has in common with the target zone, a _deleg label and the name of the target zone. For example if the triggering query is www.customer.example. and the target zone example., then the incremental deleg query name is customer._deleg.example. For another Homburg, et al. Expires 4 September 2025 [Page 11] Internet-Draft incremental-deleg March 2025 example, if the triggering query is www.faculty.university.example. and the target zone example. then the incremental deleg name is university._deleg.example. Normal DNAME, CNAME and IDELEG in AliasMode processing should happen as before, though note that when following a IDELEG RR in AliasMode the target RR type is SVCB (see Section 2). The eventual incremental deleg query response, after following all redirections caused by DNAME, CNAME and AliasMode IDELEG RRs, has three possible outcomes: 1. A IDELEG RRset in ServiceMode is returned in the response's answer section containing the delegation for the subzone. The IDELEG RRs in the RRset MUST be used to follow the referral. The TargetName data field in the IDELEG RRs in the RRset MUST be used as the names for the name servers to contact for the subzone, and the ipv4hint and ipv6hint parameters MUST be used as the IP addresses for the TargetName in the same IDELEG RR. The NS RRset and glue, in the response of the legacy query that was sent in parallel to the incremental deleg query, MUST NOT be used, but the signed DS record (or NSEC(3) records indicating that there was no DS) MUST be used in linking the DNSSEC authentication chain as which would conventionally be done with DNSSEC as well. 2. The incremental deleg query name does not exist (NXDOMAIN). There is no incremental delegation for the subzone, and the referral response for the legacy delegation MUST be processed as would be done with legacy DNS and DNSSEC processing. 3. The incremental deleg query name does exist, but resulted in a NOERROR no answer response (also known as a NODATA response). If the legacy query, did result in a referral for the same number of labels as the subdomain that the incremental deleg query was for, then there was no incremental delegation for the subzone, and the referral response for the legacy delegation MUST be processed as would be done with legacy DNS and DNSSEC processing. Otherwise, the subzone may be more than one label below the delegating zone. If the response to the legacy query resulted in a referral, then a new incremental deleg query MUST be spawned, matching the zone cut of the legacy referral response. For example if the triggering query is www.university.ac.example. and the target Homburg, et al. Expires 4 September 2025 [Page 12] Internet-Draft incremental-deleg March 2025 zone example., and the legacy response contained an NS RRset for university.ac.example., then the incremental deleg query name is university.ac._deleg.example. The response to the new incremental deleg query MUST be processed as described above, as if it was the initial incremental deleg query. If the legacy query was sent minimised and needs a followup query, then parallel to that followup query a new incremental deleg query will be sent, adding a single label to the previous incremental deleg query name. For example if the triggering query is www.university.ac.example. and the target zone is example. and the minimised legacy query name is ac.example. (which also resulted in a NOERROR no answer response), then the incremental deleg query to be sent along in parallel with the followup legacy query will become university.ac.example. Processing of the responses of those two new queries will be done as described above. 4.2. _deleg label presence Absence of the _deleg label in a zone is a clear signal that the zone does not contain any incremental deleg delegations. Recursive resolvers SHOULD NOT send any additional incremental deleg queries for zones for which it is known that it does not contain the _deleg label at the apex. The state regarding the presence of the _deleg label within a resolver can be "unknown", "known not to be present", or "known to be present". The state regarding the presence of the _deleg label can be deduced from the response of the incremental deleg query, if the target zone is signed with DNSSEC. If the target zone is unsigned, the procedure as described in the remainder of this section SHOULD be followed. When the presence of a _deleg label is "unknown", a _deleg presence test query SHOULD be sent in parallel to the next query for the unsigned target zone (though not when the target name server is known to support incremental deleg, which will be discussed in Section 5.1). The query name for the test query is the _deleg label prepended to the apex of zone for which to test presence, with query type NS. The testing query can have three possible outcomes: 1. The _deleg label does not exist within the zone, and an NXDOMAIN response is returned. Homburg, et al. Expires 4 September 2025 [Page 13] Internet-Draft incremental-deleg March 2025 The non-existence of the _deleg label MUST be cached for the duration indicated by the "minimum" RDATA field of the SOA resource record in the authority section, adjusted to the boundaries for TTL values that the resolver has (Section 4 of [RFC8767]). For the period the non-existence of the _deleg label is cached, the label is "known not to be present" and the resolver SHOULD NOT send any (additional) incremental deleg queries. 2. The _deleg label does exist within the zone but contains no data. A NOERROR response is returned with no RRs in the answer section. The existence of the _deleg name MUST be cached for the duration indicated by the "minimum" RDATA field of the SOA resource record in the authority section, adjusted to the resolver's TTL boundaries. For the period the existence of the empty non- terminal at the _deleg label is cached, the label is "known to be present" and the resolver MUST send additional incremental deleg queries as described in Section 4.1. 3. The _deleg label does exist within the zone, but is an delegation. A NOERROR legacy referral response is returned with an NS RRset in the authority section. The resolver MUST record that the zone does not have valid incremental delegations deployed for the duration indicated by the NS RRset's TTL value, adjusted to the resolver's TTL boundaries. For the period indicated by the NS RRset's TTL value, the zone is considered to *not* to have valid incremental delegations, and MUST NOT send any (additional) incremental deleg queries. 5. Optimized implementation Support for authoritative name servers enables optimized query behavior by resolvers with reduced (simultaneous) queries. Section 5.1 specifies how incremental deleg supporting authoritative name servers return referral responses for delegations. In Section 5.2 we specify how resolvers can benefit from those authoritative servers. Homburg, et al. Expires 4 September 2025 [Page 14] Internet-Draft incremental-deleg March 2025 5.1. Authoritative name server support Incremental delegations supporting authoritative name servers include the incremental delegation information (or the NSEC(3) records showing the non-existence) in the authority section of referral responses to legacy DNS queries. For example, querying the zone from Figure 6 for www.customer5.example. A, will return the following referral response: ;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 54349 ;; flags: qr ; QUERY: 1, ANSWER: 0, AUTHORITY: 5, ADDITIONAL: 2 ;; QUESTION SECTION: ;; www.customer5.example. IN A ;; ANSWER SECTION: ;; AUTHORITY SECTION: customer5.example. 3600 IN NS ns.customer5.example. customer5.example. 3600 IN DS ... customer5.example. 3600 IN RRSIG DS ... customer5._deleg.example. 3600 IN IDELEG 1 ( ns.customer5.example. alpn=h2,h3 ipv4hint=198.51.100.5 ipv6hint=2001:db8:5::1 dohpath=/dns-query{?dns} ) customer5._deleg.example. 3600 IN RRSIG IDELEG ... ;; ADDITIONAL SECTION: ns.customer5.example. 3600 IN A 198.51.100.5 ns.customer5.example. 3600 IN AAAA 2001:db8:5::1 ;; Query time: 0 msec ;; EDNS: version 0; flags: do ; udp: 1232 ;; SERVER: 192.0.2.53 ;; WHEN: Mon Feb 24 20:36:25 2025 ;; MSG SIZE rcvd: 456 Figure 7: An incremental deleg referral response The referral response in Figure 7 includes the signed IDELEG RRset in the authority section. As another example, querying the zone from Figure 6 for www.customer6.example. A, will return the following referral response: Homburg, et al. Expires 4 September 2025 [Page 15] Internet-Draft incremental-deleg March 2025 ;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 36574 ;; flags: qr ; QUERY: 1, ANSWER: 0, AUTHORITY: 9, ADDITIONAL: 2 ;; QUESTION SECTION: ;; www.customer6.example. IN A ;; ANSWER SECTION: ;; AUTHORITY SECTION: customer6.example. 3600 IN NS ns.customer6.example. customer6.example. 3600 IN DS ... customer6.example. 3600 IN RRSIG DS ... customer5._deleg.example. 1234 IN NSEC ( customer7._deleg.example. RRSIG NSEC IDELEG ) customer5._deleg.example. 1234 IN RRSIG NSEC ... example. 1234 IN NSEC ( customer5._deleg.example. NS SOA RRSIG NSEC DNSKEY ) example. 1234 IN RRSIG NSEC ... ;; ADDITIONAL SECTION: ns.customer6.example. 3600 IN A 203.0.113.1 ns.customer6.example. 3600 IN AAAA 2001:db8:6::1 ;; Query time: 0 msec ;; EDNS: version 0; flags: do ; udp: 1232 ;; SERVER: 192.0.2.53 ;; WHEN: Tue Feb 25 10:23:53 2025 ;; MSG SIZE rcvd: 744 Figure 8: Referral response without incremental deleg Next to the legacy delegation, the incremental deleg supporting authoritative returns the NSEC(3) RRs needed to show that there was no incremental delegation in the referral response in Figure 8. Querying the zone from Figure 6 for www.customer7.example. A, will return the following referral response: Homburg, et al. Expires 4 September 2025 [Page 16] Internet-Draft incremental-deleg March 2025 ;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 9456 ;; flags: qr ; QUERY: 1, ANSWER: 0, AUTHORITY: 7, ADDITIONAL: 2 ;; QUESTION SECTION: ;; www.customer7.example. IN A ;; ANSWER SECTION: ;; AUTHORITY SECTION: customer7.example. 3600 IN NS ns.customer5.example. customer7.example. 3600 IN DS ... customer7.example. 3600 IN RRSIG DS ... customer7._deleg.example. 3600 IN CNAME ( customer5._deleg.example. ) customer7._deleg.example. 3600 IN RRSIG CNAME ... customer5._deleg.example. 3600 IN IDELEG 1 ( ns.customer5.example. alpn=h2,h3 ipv4hint=198.51.100.5 ipv6hint=2001:db8:5::1 ) customer5._deleg.example. 3600 IN RRSIG IDELEG ... ;; ADDITIONAL SECTION: ns.customer5.example. 3600 IN A 198.51.100.5 ns.customer5.example. 3600 IN AAAA 2001:db8:5::1 ;; Query time: 0 msec ;; EDNS: version 0; flags: do ; udp: 1232 ;; SERVER: 192.0.2.53 ;; WHEN: Tue Feb 25 10:55:07 2025 ;; MSG SIZE rcvd: 593 Figure 9: Aliasing referral response The incremental delegation of customer7.example. is aliased to the one that is also used by customer5.example. Since both delegations are in the same zone, the authoritative name server for example. returns both the CNAME realising the alias, as well as the IDELEG RRset which is the target of the alias in Figure 9. In other cases an returned CNAME or IDELEG RR in AliasMode may need further chasing by the resolver. With unsigned zones, only if an incremental deleg delegation exists, the IDELEG RRset (or CNAME) will be present in the authority section of referral responses. If the incremental deleg does not exist, then it is simply absent from the authority section and the referral response is indistinguishable from an non supportive authoritative. Homburg, et al. Expires 4 September 2025 [Page 17] Internet-Draft incremental-deleg March 2025 5.2. Resolver behavior with authoritative name server support Incremental deleg supporting authoritative name servers will include the incremental delegation information (or the NSEC(3) records showing the non-existence) in the authority section of referral responses. For an unsigned zone, an incremental deleg supporting authoritative cannot return that an incremental delegation is absent (because of lack of an authenticated denial of existence), however with support from the served zone (the zone has the Resource Record provisioned *._deleg IN IDELEG 0 .), the authoritative name server can signal support also for unsigned zones (see Extra optimized implementation (Section 6)). If it is known that an authoritative name server supports incremental deleg, then no direct queries for the incremental delegation need to be sent in parallel to the legacy delegation query. A resolver SHOULD register that an authoritative name server supports incremental deleg when the authority section, of the returned referral responses from that authoritative name server, contains incremental delegation information. When the authority section of a referral response contains a IDELEG RRset or a CNAME on the incremental delegation name, or valid NSEC(3) RRs showing the non-existence of such IDELEG or CNAME RRset, then the resolver SHOULD register that the contacted authoritative name server supports incremental deleg for the duration indicated by the TTL for that IDELEG, CNAME or NSEC(3) RRset, adjusted to the resolver's TTL boundaries, but only if it is longer than any already registered duration. Subsequent queries SHOULD NOT include incremental deleg queries, as described in Section 4.1, to be send in parallel for the duration support for incremental deleg is registered for the authoritative name server. For example, in Figure 7, the IDELEG RRset at the incremental delegation point has TTL 3600. The resolver should register that the contacted authoritative name server supports incremental deleg for (at least) 3600 seconds (one hour). All subsequent queries to that authoritative name server SHOULD NOT include incremental deleg queries to be send in parallel. If the authority section contains more than one RRset making up the incremental delegation, then the RRset with the longest TTL MUST be taken to determine the duration for which incremental deleg support is registered. Homburg, et al. Expires 4 September 2025 [Page 18] Internet-Draft incremental-deleg March 2025 For example, in Figure 9, both a CNAME and a IDELEG RRset for the incremental delegation are included in the authority section. The longest TTL must be taken for incremental support registration, though because the TTL of both RRsets is 3600, it does not matter in this case. With DNSSEC signed zones, support is apparent with all referral responses. With unsigned zones, support is apparent only from referral responses for which an incremental delegation exists, unless the zone has the Resource Record *._deleg IN IDELEG 0 . provisioned (see Extra optimized implementation (Section 6)). If the resolver knows that the authoritative name server supports incremental deleg, _and_ a DNSSEC signed zone is being served, then all referrals SHOULD contain either an incremental delegation, or NSEC(3) records showing that the delegation does not exist. If a referral is returned that does not contain an incremental delegation nor an indication that it does not exist, then the resolver MAY register that authoritative server does not support incremental deleg and MUST send an additional incremental deleg query to find the incremental delegation (or denial of its existence). 6. Extra optimized implementation A IDELEG RRset on an incremental delegation point, with a IDELEG RR in AliasMode, aliasing to the root zone, MUST be interpreted to mean that the legacy delegation information MUST be used to follow the referral. All service parameters for such AliasMode (aliasing to the root) IDELEG RRs on the incremental delegation point, MUST be ignored. For example, such a IDELEG RRset registered on the wildcard below the _deleg label on the apex of a zone, can signal that legacy DNS referrals MUST be used for both signed and _unsigned_ zones: $ORIGIN example. @ IN SOA ns zonemaster ... *._deleg 86400 IN IDELEG 0 . customer1._deleg IN IDELEG 1 ( ns.customer1 ipv4hint=198.51.100.1,203.0.113.1 ipv6hint=2001:db8:1::1,2001:db8:2::1 ) customer3._deleg IN CNAME _dns.ns.operator1 Figure 10: Wildcard incremental deleg to control duration of detected support Homburg, et al. Expires 4 September 2025 [Page 19] Internet-Draft incremental-deleg March 2025 Resolvers SHOULD register that an authoritative name server supports incremental deleg, if such a IDELEG RRset is returned in the authority section of referral responses, for the duration of the TTL if the IDELEG RRset, adjusted to the resolver's TTL boundaries, but only if it is longer than any already registered duration. Note that this will also be included in referral responses for unsigned zones, which would otherwise not have signalling of incremental deleg support by the authoritative name server. Also, signed zones need fewer RRs to indicate that no incremental delegation exists. The wildcard expansion already shows the closest encloser (i.e. _deleg.), so only one additional NSEC(3) is needed to show non- existence of the queried for name below the closest encloser. This method of signalling that the legacy delegation MUST be used, is RECOMMENDED. 7. Priming queries Some zones, such as the root zone, are targeted directly from hints files. Information about which authoritative name servers and with capabilities, MAY be provided in a IDELEG RRset directly at the _deleg label under the apex of the zone. Priming queries from a incremental deleg supporting resolver, MUST send an _deleg. IDELEG query in parallel to the legacy NS query and process the content as if it was found through an incremental referral response. 8. How does incremental deleg meet the requirements This section will discuss how incremental deleg meets the requirements for a new delegation mechanism as described in [I-D.ietf-deleg-requirements-02] * H1. DELEG must not disrupt the existing registration model of domains. The existing zone structure including the concept of delegations from a parent zone to a child zone is left unchanged. * H2. DELEG must be backwards compatible with the existing ecosystem. The new delegations do not interfere with legacy software. The behavior of incremental deleg-aware resolvers includes a fallback to NS records if no incremental delegation is present (See Section 4.1). Homburg, et al. Expires 4 September 2025 [Page 20] Internet-Draft incremental-deleg March 2025 * H3. DELEG must not negatively impact most DNS software. Incremental deleg introduces a new RR type. Software that parses zone file format needs to be changed to support the new type. Though unknown type notation [RFC3597] can be used in some cases if no support for the new RR type is present. Existing authoritatives can serve incremental deleg zones (though less efficiently), existing signers can sign incremental deleg zones, existing diagnostic tools can query incremental deleg zones. Non- recursive DNSSEC validators can operate independently from (possibly legacy) recursive resolvers. * H4. DELEG must be able to secure delegations with DNSSEC. Incremental delegations are automatically secured with DNSSEC (if the parent zone is signed). A replacement for DS records is described in [I-D.homburg-deleg-incremental-dnssec]. * H5. DELEG must support updates to delegation information with the same relative ease as currently exists with NS records. Incremental delegations are affected by TTL like any other DNS record. * H6. DELEG must be incrementally deployable and not require any sort of flag day of universal change. Incremental deleg zones can be added without upgrading authoritatives. Incremental deleg zones still work with old resolvers and validators. Basically any combination of old and new should work, though with reduced efficiency for some combinations. * H7. DELEG must allow multiple independent operators to simultaneously serve a zone. Incremental deleg allows for multiple IDELEG records. This allows multiple operators to serve the zone. * S1. DELEG should facilitate the use of new DNS transport mechanisms New transports are already defined for the DNS mode of SVCB ([RFC9461]). The same parameters are used for IDELEG. * S2. DELEG should make clear all of the necessary details for contacting a service Homburg, et al. Expires 4 September 2025 [Page 21] Internet-Draft incremental-deleg March 2025 Most of the needed SVCB parameters are already defined in existing standards. The exception is a replacement for the DS records, which is described in [I-D.homburg-deleg-incremental-dnssec]. * S3. DELEG should minimize transaction cost in its usage. Assuming Qname-minimisation, there are no extra queries needed in most cases if the authoritative name server has incremental deleg support. The exception is when the parent zone is not signed and has no incremental deleg records. In that case, one extra query is needed when the parent zone is first contacted (and every TTL). Additional queries may be needed to resolve aliases. * S4. DELEG should simplify management of a zone's DNS service. Zone management can be simplified using the alias mode of IDELEG. This allows the zone operator to change the details of the delegation without involving the parent zone. Draft [I-D.homburg-deleg-incremental-dnssec] defines the dnskeyref parameter which offers the same simplification for DNSSEC delegations. * S5. DELEG should allow for backward compatibility to the conventional NS-based delegation mechanism. NS records and glue can be extracted from the IDELEG record assuming no aliasing is used. The ds parameter in [I-D.homburg-deleg-incremental-dnssec] has the same value as the rdata of a DS record. * S6. DELEG should be extensible and allow for the easy incremental addition of new delegation features after initial deployment. SVCB-style records are extensible by design. * S7. DELEG should be able to convey a security model for delegations stronger than currently exists with DNSSEC. Increment delegations are protected by DNSSEC, unlike NS records at the parent zone. 9. Comparison with other delegation mechanisms Table Table 1 provides an overview of when extra queries, in parallel to the legacy query, are sent. Homburg, et al. Expires 4 September 2025 [Page 22] Internet-Draft incremental-deleg March 2025 +=+=====+=======+==========++=====================+================+ | | apex| auth | _deleg || ._deleg. | _deleg. | | |query|support| presence || IDELEG | A | +=+=====+=======+==========++=====================+================+ |1| Yes | * | * || | | +-+-----+-------+----------++---------------------+----------------+ |2| No | * | No || | | +-+-----+-------+----------++---------------------+----------------+ |3| No | Yes | * || | | +-+-----+-------+----------++---------------------+----------------+ |4| No |Unknown| Yes || X | | +-+-----+-------+----------++---------------------+----------------+ |5| No |Unknown| Unknown || X | only for | | | | | || | unsigned zones | +-+-----+-------+----------++---------------------+----------------+ Table 1: Additional queries in parallel to the legacy query The three headers on the left side of the table mean the following: apex query: Whether the query is for the apex of the target zone. "Yes" means an apex query, "No" means a query below the apex which may be delegated auth support: Whether or not the target authoritative server supports incremental deleg. "Yes" means it supports it and "Unknown" means support is not detected. "*" means it does not matter _deleg presence: Whether or not the _deleg label is present in the target zone (and thus incremental delegations) On the right side of the table are the extra queries, to be sent in parallel with the legacy query. The _deleg presence test query (most right column) only needs to be sent to unsigned target zones, because its non-existence will be show in the NSEC(3) records showing the non-existence of the incremental delegation (second from right column). If the query name is the same as the apex of the target zone, no extra queries need to be sent (Row 1). If the _deleg label is known not to exist in the target zone (Row 2) or if the target name server is known to support incremental deleg (Row 3), no extra queries need to be sent. Only if it is unknown that the target name server supports incremental deleg, and the _deleg label is known to exist in the target zone (Row 4) or it is not known whether or not the _deleg Homburg, et al. Expires 4 September 2025 [Page 23] Internet-Draft incremental-deleg March 2025 label exists (Row 5), and extra incremental deleg query is sent in parallel to the legacy query. If the target zone is unsigned, presence of the _deleg label needs to be tested explicitly (Row 5). 9.1. Comparison with legacy delegations 9.1.1. The delegation point Legacy delegations are realized by an non-authoritative NS RRset at the name of the delegated zone, but in the delegating zone (the parent side of the zone cut). However, there is another NS RRset by the same name, but now authoritative, in the delegated zone (the child side of the zone cut). Some resolvers prefer to use the authoritative child side NS RRset (see Section 5.4.1 of [RFC2181]) for contacting the authoritative name servers of the delegated zone, and will use it to reach the zone if they encounter the child side NS RRset authoritatively in responses. Some resolvers query explicitly for the authoritative child side NS RRset [I-D.ietf-dnsop-ns-revalidation]. However, these NS RRsets can differ in content leading to errors and inconsistencies (see Section 3 of [I-D.ietf-dnsop-ns-revalidation]). Incremental deleg eliminates these issues by placing the referral information, not at the name of the delegated zone, but authoritatively in the delegating zone. Having the referral information at an authoritative location brings clarity. There can be no misinterpretation about who is providing the referral (the delegating zone, or the delegated zone). In an future world where all delegations would be incremental delegations, all names will only be authoritative data, derivable from the name, for resolvers and other applications alike. 9.1.2. Legacy referrals Resolvers that support only legacy referrals will be on the internet for the foreseeable future, therefore a legacy referral MUST always be provided alongside the incremental referral. Legacy referrals can be deduced from the incremental delegation. An authoritative could (in some cases) synthesize the legacy referral from the incremental delegation, however this is not RECOMMENDED. It introduces an element of dynamism which is at the time of writing not part of authoritative name server behavior specification. Moreover, authoritative name servers could transfer the zone data to non incremental deleg supporting and aware name servers, which would not have this feature. We leave provisioning of legacy referrals from incremental delegations (for now) out of scope for this document. Homburg, et al. Expires 4 September 2025 [Page 24] Internet-Draft incremental-deleg March 2025 9.1.3. Number of queries Legacy resolvers that do not do DNS Query Name Minimisation, will get a referral in a single query. The resolution process with incremental delegations must find the exact zone cut explicitly, comparable with DNS Query Name Minimisation. The query increase to find the zone cut (and referral) is comparable to that of a resolver performing DNS Query Name minimisation. 9.2. Comparison with Name DNS Query Name Minimisation There are no extra queries needed in most cases if the authoritative name server has incremental deleg support. The exception is when the parent zone is not signed and has no incremental deleg records. In that case, one extra query is needed when the parent zone is first contacted (and every TTL) 9.3. Comparison with [I-D.wesplaap-deleg] +=============================+===================================+ | [?I-D.wesplaap-deleg] | [this document] | +=============================+===================================+ | Requires implementation in | Only resolver implementation | | both authoritative name | required. But optimized with | | server as well as in the | updated authoritative software. | | resolver, DNSSEC signers | | | and validators and all | | | other DNS software | | +-----------------------------+-----------------------------------+ | DELEG resolvers need to | IDELEG resolvers can query for | | contact DELEG | the incremental delegation data, | | authoritatives directly | therefore direct contact with | | | IDELEG supporting authoritatives | | | is not necessary. All legacy | | | infrastructure (including | | | forwarders etc.) is supported. | +-----------------------------+-----------------------------------+ | DNSKEY flag needed to | No DNSKEY flag needed. | | signal IDELEG support with | Separation of concerns. | | all authoritative name | | | servers that serve the | | | parent (delegating) domain. | | | Special requirements for | | | the child domain. | | +-----------------------------+-----------------------------------+ | Authoritative name servers | Authoritative name servers may be | | need to be updated all at | updated gradually for | | once | optimization | Homburg, et al. Expires 4 September 2025 [Page 25] Internet-Draft incremental-deleg March 2025 +-----------------------------+-----------------------------------+ | New semantics about what is | Works with current DNS and DNSSEC | | authoritative (BOGUS with | semantics. Easier to implement. | | current DNSSEC validators) | | +-----------------------------+-----------------------------------+ | No extra queries | One extra query, in parallel to | | | the legacy query, _per | | | authoritative_ server when | | | incremental deleg support is not | | | yet detected, and one extra query | | | _per unsigned zone_ to determine | | | presence of the _deleg label | +-----------------------------+-----------------------------------+ Table 2: Comparison of [I-D.wesplaap-deleg] with [this document] 10. Implementation Status *Note to the RFC Editor*: please remove this entire section before publication. We are using RR type code 65280 for experiments. Jesse van Zutphen has built a proof of concept implementation supporting incremental delegations as specified in a previous version of this document [I-D.homburg-deleg-incremental-deleg-00] for the Unbound recursive resolver as part of his master thesis for the Security and Network Engineering master program of the University of Amsterdam [JZUTPHEN]. Jesse's implementation has been adapted to query for the IDELEG RR types (with code point 65280). This version is available in the ideleg branch of the NLnetLabs/unbound github repository [IDELEG4UNBOUND]. Note that this implementation does not yet support optimized behaviour (Section 5.2), and also does not yet follow AliasMode IDELEG RRs. The ldns DNS library and tools software has been extended with support for IDELEG, which is available in the features/ideleg branch of the NLnetLabs/ldns github repository [IDELEG4LDNS]. This includes support for IDELEG in the DNS lookup utility drill, as well as in the DNSSEC zone signer ldns-signzone and all other tools and examples included with the ldns software. Wouter Petri has built a proof of concept support for IDELEG in the NSD authoritative name server software as part of a research project for the Security and Network Engineering master program of the University of Amsterdam [WPETRI]. The source code of his implementation is available on github [IDELEG4NSD]. Homburg, et al. Expires 4 September 2025 [Page 26] Internet-Draft incremental-deleg March 2025 Wouter's implementation is serving the ideleg.net. domain, containing a variety of different incremental delegations, for evaluation purposes. We are planning to provide information about the deployment, including what software to evaluate these delegations, at http://ideleg.net/ (http://ideleg.net/), hopefully before the IETF 122 in Bangkok (https://datatracker.ietf.org/meeting/122/ proceedings). 11. Security Considerations Incremental deleg moves the location of referral information to a unique location that currently exists. However, as this is a new approach, thought must be given to usage. There must be some checks to ensure that the registering a _deleg subdomain happens at the time the domain is provisioned. The same care needs to be addressed when a domain is deprovisioned that the _deleg is removed. This is similar to what happens to NS A records deployed in parent zones to act as Glue. While the recommendation is to deploy DNSSEC with incremental deleg, it is not mandatory. However, using incremental deleg with unsigned zones can create possibilities of domain hijackings. This could be hard to detect when not speaking directly to the authoritative name server. This risk of domain hijacking is not expected to increase significantly compared to the situation without incremental deleg. There are bound to be other considerations. 12. IANA Considerations 12.1. IDELEG RR type IANA is requested to update the "Resource Record (RR) TYPEs" registry under the "Domain Name System (DNS) Parameters" registry group as follows: +========+=======+============+=================+ | TYPE | Value | Meaning | Reference | +========+=======+============+=================+ | IDELEG | TBD | Delegation | [this document] | +--------+-------+------------+-----------------+ Table 3 12.2. _deleg Node Name Per [RFC8552], IANA is requested to add the following entry to the DNS "Underscored and Globally Scoped DNS Node Names" registry: Homburg, et al. Expires 4 September 2025 [Page 27] Internet-Draft incremental-deleg March 2025 +=========+============+=================+ | RR Type | _NODE NAME | Reference | +=========+============+=================+ | IDELEG | _deleg | [this document] | +---------+------------+-----------------+ Table 4: Entry in the Underscored and Globally Scoped DNS Node Names registry 13. References 13.1. 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, . [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, . [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September 2003, . [RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012, . [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., and P. Hoffman, "Specification for DNS over Transport Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, . [RFC8767] Lawrence, D., Kumari, W., and P. Sood, "Serving Stale Data to Improve DNS Resiliency", RFC 8767, DOI 10.17487/RFC8767, March 2020, . Homburg, et al. Expires 4 September 2025 [Page 28] Internet-Draft incremental-deleg March 2025 [RFC9156] Bortzmeyer, S., Dolmans, R., and P. Hoffman, "DNS Query Name Minimisation to Improve Privacy", RFC 9156, DOI 10.17487/RFC9156, November 2021, . [RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, May 2022, . [RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding and Parameter Specification via the DNS (SVCB and HTTPS Resource Records)", RFC 9460, DOI 10.17487/RFC9460, November 2023, . [RFC9461] Schwartz, B., "Service Binding Mapping for DNS Servers", RFC 9461, DOI 10.17487/RFC9461, November 2023, . [STD13] Internet Standard 13, . At the time of writing, this STD comprises the following: Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, . Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . 13.2. Informative References [BCP219] Best Current Practice 219, . At the time of writing, this BCP comprises the following: Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219, RFC 9499, DOI 10.17487/RFC9499, March 2024, . [I-D.homburg-deleg-incremental-deleg-00] Homburg, P., van Zutphen, J., and W. Toorop, "Incrementally Deployable Extensible Delegation for DNS", Work in Progress, Internet-Draft, draft-homburg-deleg- incremental-deleg-00, 8 July 2024, . Homburg, et al. Expires 4 September 2025 [Page 29] Internet-Draft incremental-deleg March 2025 [I-D.homburg-deleg-incremental-dnssec] Homburg, P. and W. Toorop, "Incrementally Deployable DNSSEC Delegation", Work in Progress, Internet-Draft, draft-homburg-deleg-incremental-dnssec-00, 16 January 2025, . [I-D.ietf-deleg-requirements-02] Lawrence, Lewis, E., Reid, J., and T. Wicinski, "Problem Statement and Requirements for an Improved DNS Delegation Mechanism abbrev: DNS DELEG Requirements", Work in Progress, Internet-Draft, draft-ietf-deleg-requirements- 02, 12 October 2024, . [I-D.ietf-dnsop-ns-revalidation] Huque, S., Vixie, P. A., and W. Toorop, "Delegation Revalidation by DNS Resolvers", Work in Progress, Internet-Draft, draft-ietf-dnsop-ns-revalidation-09, 27 February 2025, . [I-D.ietf-tls-esni] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS Encrypted Client Hello", Work in Progress, Internet-Draft, draft-ietf-tls-esni-23, 19 February 2025, . [I-D.tapril-ns2] April, T., "Parameterized Nameserver Delegation with NS2 and NS2T", Work in Progress, Internet-Draft, draft-tapril- ns2-01, 13 July 2020, . [I-D.wesplaap-deleg] April, T., Špaček, P., Weber, R., and Lawrence, "Extensible Delegation for DNS", Work in Progress, Internet-Draft, draft-wesplaap-deleg-02, 18 February 2025, . [IDELEG4LDNS] Toorop, W., "A proof of concept support for IDELEG in the ldns DNS library and tools", n.d., . Homburg, et al. Expires 4 September 2025 [Page 30] Internet-Draft incremental-deleg March 2025 [IDELEG4NSD] Petri, W., "A proof of concept support for IDELEG in the NSD authoritative name server software", n.d., . [IDELEG4UNBOUND] van Zutphen, J. and P. Homburg, "A proof of concept implementation of incremental deleg", n.d., . [JZUTPHEN] van Zutphen, J., "Extensible delegations in DNS Recursive resolvers", n.d., . [RFC8552] Crocker, D., "Scoped Interpretation of DNS Resource Records through "Underscored" Naming of Attribute Leaves", BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019, . [WPETRI] Petri, W., "Extensible delegations in authoritative nameservers", n.d., . Acknowledgments The idea to utilize SVCB based RRs to signal capabilities was first proposed by Tim April in [I-D.tapril-ns2]. The idea to utilize SVCB for extensible delegations (and also the idea described in this document) emerged from the DNS Hackathon at the IETF 118. The following participants contributed to this brainstorm session: Vandan Adhvaryu, Roy Arends, David Blacka, Manu Bretelle, Vladimír Čunát, Klaus Darilion, Peter van Dijk, Christian Elmerot, Bob Halley, Philip Homburg, Shumon Huque, Shane Kerr, David C Lawrence, Edward Lewis, George Michaelson, Erik Nygren, Libor Peltan, Ben Schwartz, Petr Špaček, Jan Včelák and Ralf Weber Authors' Addresses Philip Homburg NLnet Labs Email: philip@nlnetlabs.nl Tim Wicinski Cox Communications Homburg, et al. Expires 4 September 2025 [Page 31] Internet-Draft incremental-deleg March 2025 Email: tjw.ietf@gmail.com Jesse van Zutphen University of Amsterdam Email: Jesse.vanZutphen@os3.nl Willem Toorop NLnet Labs Email: willem@nlnetlabs.nl Homburg, et al. Expires 4 September 2025 [Page 32]