| Internet-Draft | DELEG | February 2025 |
| April, et al. | Expires 22 August 2025 | [Page] |
A delegation in the Domain Name System (DNS) is a mechanism that enables efficient and distributed management of the DNS namespace. It involves delegating authority over subdomains to specific DNS servers via NS records, allowing for a hierarchical structure and distributing the responsibility for maintaining DNS records.¶
An NS record contains the hostname of the nameserver for the delegated namespace. Any facilities of that nameserver must be discovered through other mechanisms. This document proposes a new extensible DNS record type, DELEG, for delegation the authority for a domain. Future documents then can use this mechanism to use additional information about the delegated namespace and the capabilities of authoritative nameservers for the delegated namespace.¶
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 22 August 2025.¶
Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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In the Domain Name System [STD13], subdomains within the domain name hierarchy are indicated by delegations to servers which are authoritative for their portion of the namespace. The DNS records that do this, called NS records, contain hostnames of nameservers, which resolve to addresses. No other information is available to the resolver. It is limited to connect to the authoritative servers over UDP and TCP port 53. This limitation is a barrier for efficient introduction of new DNS technology.¶
The proposed DELEG record type remedies this problem by providing extensible parameters to indicate capabilities and additional information, such as glue that a resolver may use for the delegated authority. It is authoritative and thus signed in the parent side of the delegation making it possible to validate all delegation parameters (names and glue records) with DNSSEC.¶
This document only shows how DELEG can be used instead of or along side a NS record to create a delegation. Future documents can use the extensible mechanism for more advanced features like connecting to a name server with an encrypted transport.¶
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.¶
Terminology regarding the Domain Name System comes from [BCP219], with addition terms defined here:¶
The DELEG record uses a new resource record type, whose contents are identical to the SVCB record defined in [RFC9460]. For extensions SVCB and DELEG use Service Parameter Keys (SvcParamKeys) and new SvcParamKeys that might be needed also will use the existing IANA Registry.¶
DELEG can only have two priorities 0 indicating INCLUDE and 1 indicating a DIRECT delegation. These terms MUST be used in the presentation format of the DELEG record.¶
INCLUDE and DIRECT delegation can be mixed within an RRSet¶
The final INCLUDE target is an SVCB record, though there can be further indirection using CNAME or AliasMode SVCB records.¶
There can be multiple INCLUDE DELEG records, but further indirections through SVCB records have to comply with [RFC9460] in that there can be only one AliasMode SVCB record per name.¶
In order to not allow unbound indirection of DELEG records the maximum number of indirections, CNAME or AliasMode SVCB is 4.¶
The SVCB IPv4hint and IPv6hint parameters keep their key values of 4 and 6, but the presentation format with DELEG MUST be Glue4 and Glue6.¶
Glue4 and Glue6 records when present MUST be used to connect to the delegated name server.¶
The target of a DELEG record MUST NOT be '.' and for INCLUDE must be outside of the delegated domain and for DIRECT in domain delegations below the zone cut.¶
The DELEG record creates a zone cut similar to the NS record so all data at or below the zone cut has to be resolved using the name servers defined in the DELEG record.¶
A DELEG RRset MAY be present at a delegation point. The DELEG RRset MAY contain multiple records. DELEG RRsets MUST NOT appear at a zone's apex.¶
A DELEG RRset MAY be present with or without NS or DS RRsets at the delegation point.¶
An authoritative server that is DELEG aware MUST put all DELEG resource records for the delegation into the authority section when the resolver has signalled DELEG support. It SHOULD NOT supply DELEG records in the response when receiving a request without the DE bit.¶
If the delegation does not have DELEG records the authoritative server MUST send the NS records and, if the zone is DNSSEC signed, prove the absence of the DELEG RRSet.¶
A resolver that is DELEG aware MUST signal its support by sending the DE bit when iterating and MUST use the DELEG records in the referral response.¶
For a long time there will be both DELEG and NS needed for delegation. As both methods should be configured to get to a proper resolution it is not necessary to send both in a referral response. We therefore purpose an EDNS flag to be use similar to the DO Bit for DNSSEC to be used to signal that the sender understands DELEG and does not need NS or glue information in the referral.¶
This bit is referred to as the "DELEG" (DE) bit. In the context of the EDNS0 OPT meta-RR, the DE bit is the TBD of the "extended RCODE and flags" portion of the EDNS0 OPT meta-RR, structured as follows (to be updated when assigned):¶
+0 (MSB) +1 (LSB)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0: | EXTENDED-RCODE | VERSION |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2: |DO|CO|DE| Z |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
¶
Setting the DE bit to one in a query indicates to the server that the resolver is able to accept delegations using DELEG only. The DE bit cleared (set to zero) indicates the resolver is unprepared to handle DELEG and hence can only be served NS, DS and glue in a delegation response. The DE bit of the query MUST be copied in the response.¶
As the DELEG record is authoritative in the parent zone of a zone cut similar to DS it has to be signed in the parent zone.¶
In order for the validator to understand that the delegation uses DELEG this draft introduces a new DNSKEY flag TBD. When this flag is set for the key that signs the DS or DELEG record, usually the zone signing key (ZSK), and the request has signalled that it understands DELEG an authenticated denial of existence MUST be send with the referral response, so that a DELEG aware validator can prove the existence or absence of a DELEG record and detect a downgrade attack.¶
A Validating Stub Resolver that is DELEG aware has to use a Security-Aware Resolver that is DELEG aware and if it is behind a forwarder this has to be security and DELEG aware as well.¶
IANA is requested to allocate the DELEG RR in the Resource Record (RR) TYPEs registry, with the meaning of "enchanced delegation information" and referencing this document.¶
IANA is requested to assign a new bit in the DNSKEY RR Flags registry ([RFC4034]) for the DELEG bit (N), with the descripion "DELEG" and referencing this document.¶
IANA is requested to assign a bit from the EDNS Header Flags registry ([RFC6891]), with the abbreviation DE, the description "DELEG enabled" and referencing this document.¶
For the RDATA parameters to a DELEG RR, the DNS Service Bindings (SVCB) registry ([RFC9460]) is used. This document requests no new assignments to that registry, though it is expected that future DELEG work will.¶
The following example shows an excerpt from a signed root zone. It shows the delegation point for "example." and "test."¶
The "example." delegation has DELEG and NS records. The "test." delegation has DELEG but no NS records.¶
example. 300 IN DELEG 1 a.example. Glue4=192.0.2.1 (
Glue6=2001:DB8::1 )
example. 300 IN DELEG 0 ns2.example.net.
example. 300 IN DELEG 0 ns3.example.org.
example. 300 IN RRSIG DELEG 13 4 300 20250214164848 (
20250207134348 21261 . HyDHYVT5KcqWc7J..= )
example. 300 IN NS a.example.
example. 300 IN NS b.example.net.
example. 300 IN NS c.example.org.
example. 300 IN DS 65163 13 2 5F86F2F3AE2B02...
example. 300 IN RRSIG DS 13 4 300 20250214164848 (
20250207134348 21261 . O0k558jHhyrC21J..= )
example. 300 IN NSEC a.example. NS DS RRSIG NSEC DELEG
example. 300 IN RRSIG NSEC 13 4 300 20250214164848 (
20250207134348 21261 . 1Kl8vab96gG21Aa..= )
a.example. 300 IN A 192.0.2.1
a.example. 300 IN AAAA 2001:DB8::1
¶
The "test." delegation point has a DELEG record and no NS record.¶
test. 300 IN DELEG 0 ns2.example.net
test. 300 IN RRSIG DELEG 13 4 300 20250214164848 (
20250207134348 21261 . 98Aac9f7A1Ac26Q..= )
test. 300 IN NSEC a.test. RRSIG NSEC DELEG
test. 300 IN RRSIG NSEC 13 4 300 20250214164848 (
20250207134348 21261 . kj7YY5tr9h7UqlK..= )
¶
;; Header: QR RCODE=0
;;¶
;; Question
foo.example. IN MX¶
;; Answer
;; (empty)¶
;; Authority
example. 300 IN NS a.example.
example. 300 IN NS b.example.net.
example. 300 IN NS c.example.org.¶
;; Additional
a.example. 300 IN A 192.0.2.1
a.example. 300 IN AAAA 2001:DB8::1¶
;; Header: QR DO RCODE=0
;;
;; Question
foo.example. IN MX
;; Answer
;; (empty)
;; Authority
example. 300 IN NS a.example.
example. 300 IN NS b.example.net.
example. 300 IN NS c.example.org.
example. 300 IN DS 65163 13 2 5F86F2F3AE2B02...
example. 300 IN RRSIG DS 13 4 300 20250214164848 (
20250207134348 21261 . O0k558jHhyrC21J..= )
;; Additional
a.example. 300 IN A 192.0.2.1
a.example. 300 IN AAAA 2001:DB8::1
¶
;; Header: QR DO AA RCODE=3
;;
;; Question
foo.test. IN MX
;; Answer
;; (empty)
;; Authority
. 300 IN SOA ...
. 300 IN RRSIG SOA ...
. 300 IN NSEC aaa NS SOA RRSIG NSEC DNSKEY ZONEMD
. 300 IN RRSIG NSEC 13 4 300
test. 300 IN NSEC a.test. RRSIG NSEC DELEG
test. 300 IN RRSIG NSEC 13 4 300 20250214164848 (
20250207134348 21261 . aBFYask;djf7UqlK..= )
;; Additional
;; (empty)
¶
;; Header: QR DE RCODE=0
;;
;; Question
foo.example. IN MX
;; Answer
;; (empty)
;; Authority
example. 300 IN DELEG 1 a.example. Glue4=192.0.2.1 (
Glue6=2001:DB8::1 )
example. 300 IN DELEG 0 ns2.example.net.
example. 300 IN DELEG 0 ns3.example.org.
;; Additional
;; (empty)
¶
;; Header: QR AA RCODE=0 ;; ;; Question foo.test. IN MX ;; Answer ;; (empty) ;; Authority test. 300 IN DELEG 0 ns2.example.net ;; Additional ;; (empty)¶
;; Header: QR DO DE RCODE=0
;;
;; Question
foo.example. IN MX
;; Answer
;; (empty)
;; Authority
example. 300 IN DELEG 1 a.example. Glue4=192.0.2.1 (
Glue6=2001:DB8::1 )
example. 300 IN DELEG 0 ns2.example.net.
example. 300 IN DELEG 0 ns3.example.org.
example. 300 IN RRSIG DELEG 13 4 300 20250214164848 (
20250207134348 21261 . HyDHYVT5KcqWc7J..= )
example. 300 IN DS 65163 13 2 5F86F2F3AE2B02...
example. 300 IN RRSIG DS 13 4 300 20250214164848 (
20250207134348 21261 . O0k558jHhyrC21J..= )
;; Additional
a.example. 300 IN A 192.0.2.1
a.example. 300 IN AAAA 2001:DB8::1
¶
;; Header: QR DO DE AA RCODE=3
;;
;; Question
foo.test. IN MX
;; Answer
;; (empty)
;; Authority
. 300 IN SOA ...
. 300 IN RRSIG SOA ...
. 300 IN NSEC aaa NS SOA RRSIG NSEC DNSKEY ZONEMD
. 300 IN RRSIG NSEC 13 4 300
test. 300 IN NSEC a.test. RRSIG NSEC DELEG
test. 300 IN RRSIG NSEC 13 4 300 20250214164848 (
20250207134348 21261 . aBFYask;djf7UqlK..= )
;; Additional
;; (empty)
¶
This document is heavily based on past work done by Tim April in [I-D.tapril-ns2] and thus extends the thanks to the people helping on this which are: John Levine, Erik Nygren, Jon Reed, Ben Kaduk, Mashooq Muhaimen, Jason Moreau, Jerrod Wiesman, Billy Tiemann, Gordon Marx and Brian Wellington.¶
PLEASE REMOVE THE THIS SECTION PRIOR TO PUBLICATION.¶
PLEASE REMOVE THE THIS SECTION PRIOR TO PUBLICATION.¶