



deleg                                                           T. April
Internet-Draft                                               Google, LLC
Updates: 1034, 1035, 4035, 6672, 6840 (if                      P. Špaček
         approved)                                                   ISC
Intended status: Standards Track                                R. Weber
Expires: 19 April 2026                               Akamai Technologies
                                                             D. Lawrence
                                                              Salesforce
                                                         16 October 2025


                     Extensible Delegation for DNS
                          draft-ietf-deleg-04

Abstract

   This document proposes a new extensible method for the delegation of
   authority for a domain in the Domain Name System (DNS) using DELEG
   and DELEGI records.

   A delegation in the DNS enables efficient and distributed management
   of the DNS namespace.  The traditional DNS delegation is based on NS
   records which contain only hostnames of servers and no other
   parameters.  The new delegation records are extensible, can be
   secured with DNSSEC, and eliminate the problem of having two sources
   of truth for delegation information.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at https://github.com/
   ietf-wg-deleg/draft-ietf-deleg-base/tree/gh-pages.  Status
   information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-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/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-deleg/draft-ietf-deleg-base/.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.



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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 19 April 2026.

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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  DELEG and DELEGI Resource Record Types  . . . . . . . . . . .   5
     2.1.  Presentation Format . . . . . . . . . . . . . . . . . . .   6
     2.2.  RDATA Wire Format . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Overview of Differences between DELEG and DELEGI
           Semantics . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Use of DELEG Records  . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Resolvers . . . . . . . . . . . . . . . . . . . . . . . .   8
       3.1.1.  Signaling DELEG Support . . . . . . . . . . . . . . .   8
       3.1.2.  Referral  . . . . . . . . . . . . . . . . . . . . . .   9
       3.1.3.  Parent-side types, QTYPE=DELEG  . . . . . . . . . . .   9
       3.1.4.  Algorithm for "Finding the Best Servers to Ask" . . .   9
       3.1.5.  Name Server Information for Delegation  . . . . . . .  12
       3.1.6.  Populating the SLIST from DELEG and DELEGI Records  .  13
     3.2.  Authoritative Servers . . . . . . . . . . . . . . . . . .  14
       3.2.1.  DELEG-aware Clients . . . . . . . . . . . . . . . . .  14
       3.2.2.  DELEG-unaware Clients . . . . . . . . . . . . . . . .  15
     3.3.  DNSSEC Signers  . . . . . . . . . . . . . . . . . . . . .  17
     3.4.  DNSSEC Validators . . . . . . . . . . . . . . . . . . . .  18



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       3.4.1.  Clarifications on Nonexistence Proofs . . . . . . . .  18
       3.4.2.  Insecure Delegation Proofs  . . . . . . . . . . . . .  18
       3.4.3.  Referral downgrade protection . . . . . . . . . . . .  19
       3.4.4.  Chaining  . . . . . . . . . . . . . . . . . . . . . .  19
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
     4.1.  Preventing Over-work Attacks  . . . . . . . . . . . . . .  19
     4.2.  Preventing Downgrade Attacks  . . . . . . . . . . . . . .  20
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     5.1.  Changes to Existing Registries  . . . . . . . . . . . . .  20
     5.2.  New Registry for Delegation Information . . . . . . . . .  21
       5.2.1.  Procedure . . . . . . . . . . . . . . . . . . . . . .  21
       5.2.2.  Initial Contents  . . . . . . . . . . . . . . . . . .  21
     5.3.  Temporary Assignments . . . . . . . . . . . . . . . . . .  22
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  24
     A.1.  Root zone file  . . . . . . . . . . . . . . . . . . . . .  24
     A.2.  Example.org zone file . . . . . . . . . . . . . . . . . .  25
     A.3.  Example.net zone file . . . . . . . . . . . . . . . . . .  26
     A.4.  Responses . . . . . . . . . . . . . . . . . . . . . . . .  26
       A.4.1.  DO bit clear, DE bit clear  . . . . . . . . . . . . .  26
       A.4.2.  DO bit set, DE bit clear  . . . . . . . . . . . . . .  27
       A.4.3.  DO bit clear, DE bit set  . . . . . . . . . . . . . .  29
       A.4.4.  DO bit set, DE bit set  . . . . . . . . . . . . . . .  30
     A.5.  DELEGI Interpretation . . . . . . . . . . . . . . . . . .  31
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   In the Domain Name System, responsibility for each subdomain within
   the domain name hierarchy can be delegated to different servers,
   which makes them authoritative for their portion of the namespace.

   The original DNS record that does this, called an NS record, contains
   only the hostname of a single name server and no other parameters.
   The resolver needs to resolve these names into usable addresses and
   infer other required parameters, such as the transport protocol and
   any other protocol features.  Moreover, the NS record set exists in
   two places--one at the delegation point, and the other, possibly
   different, in the child zone.  The DNS Security Extensions (DNSSEC)
   protect only one copy, those in the child zone.








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   These properties of NS records limit resolvers to unencrypted UDP and
   TCP port 53, and this initial contact cannot be protected with
   DNSSEC.  Even if these two problems were somehow solved, the NS
   record does not offer extensibility for any other parameters.  This
   limitation is a barrier for the efficient introduction of new DNS
   technology.

   The proposed DELEG and DELEGI resource record (RR) types remedy this
   problem by providing extensible parameters to indicate server
   capabilities and additional information, such as other transport
   protocols that a resolver may use.

   The DELEG record creates a new delegation.  It is authoritative in
   the parent side of delegation and thus can be signed with DNSSEC.
   This makes it possible to validate all delegation parameters,
   including those of future extensions.

   The DELEGI record is an auxiliary record which does not create a
   delegation by itself but provides an optional layer of indirection.
   It can be used to share the same delegation information across any
   number of zones.  DELEGI is treated like regular authoritative
   record.

   The DELEG record can be used instead of or alongside a NS record to
   create a delegation.  The combination of DELEG+NS is fully compatible
   with old resolvers, facilitating the incremental rollout of this new
   method of delegation.

   Future documents can use the extensibility mechanism for more
   advanced features like connecting to a name server with an encrypted
   transport.

1.1.  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.

   Terminology regarding the Domain Name System comes from [BCP219],
   with addition terms defined here:

   *  legacy delegation: A delegation that is done with an NS RRset

   *  legacy response: A response that does not use the DELEG protocol
      described in this document




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   *  DELEG-aware: An authoritative server or resolver that follows the
      protocol defined in this document

   *  DELEG-unaware: An authoritative server or resolver that does not
      follow the protocol defined in this document

2.  DELEG and DELEGI Resource Record Types

   The DELEG record, RR type TBD, and the DELEGI record, RR type TBD2
   (different from that of DELEG), have the same wire and presentation
   formats, but their semantics are different as described in a
   following section.  These records are defined for the IN class.

   The record format is based on the extensible key=value list that was
   originally defined as "SvcParams" for the SVCB record type [RFC9460].
   Unlike SVCB, the DELEG protocol does not have "SvcPriority" and
   "TargetName" fields.  The keys in the DELEG protocol are different
   than those used in SVCB.  To avoid confusion between the two
   protocols, the list of key=value parameters used by the DELEG
   protocol are called DelegInfos and will be tracked in their own IANA
   registry for Delegation Information.

   The following rules are adapted from SVCB, but with changed names:

   *  The whole RDATA consists of a single list called "DelegInfos".

   *  DelegInfos consists of individual DelegInfo key=value pairs.

   *  Each DelegInfo pair has DelegInfoKey and a possibly optional
      DelegInfoValue.

   *  Each DelegInfo has a specified presentation format and wire
      encoding.

   *  Each DelegInfoKey has a presentation name and a registered key
      number.

   *  Each DelegInfoValue is in a format specific to its DelegInfoKey.

   Implementations can reuse the same code to parse SvcParams and
   DelegInfos and only plug in a different list of key=value pairs for
   SVCB/HTTPS and DELEG/DELEGI record families.

   The initial set of DelegInfoKeys and their formats are defined in
   Section 3.1.5.






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2.1.  Presentation Format

   The RDATA presentation format of the DELEG and DELEGI resource
   records consists of a single list, DelegInfos.

   The DelegInfos presentation format is defined exactly the same as
   SvcParams in Section 2.1 of [RFC9460].  The following rules are
   adapted from SVCB, but with changed names:

   *  DelegInfos is a whitespace-separated list with each DelegInfo
      consisting of a DelegInfoKey=DelegInfoValue pair, or a standalone
      DelegInfoKey.

   *  Individual element definitions are the same as [RFC9460]:

      -  The DelegInfo syntax is the same as SvcParam, but it references
         DelegInfo elements instead of SvcParam elements.

      -  DelegInfoKey syntax is the same as SvcParamKey.

      -  The syntax for unknown keys in Section 2.1 of [RFC9460]
         applies.

      -  The DelegInfoValue syntax is the same as SvcParamValue.

      -  The rules from Appendix A of [RFC9460] apply.

   *  All the requirements in Section 2.1 of [RFC9460] apply.

   DelegInfos MAY be zero-length; this is similar to what is allowed in
   SVCB records.  A record with a zero-length DelegInfos field has no
   effect on the SLIST processing for resolvers.

2.2.  RDATA Wire Format

   The RDATA portion of the DELEG and DELEGI resource record has
   variable length and entirely consists of a single "DelegInfos"
   element:

       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       /                         DelegInfos                            /
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the DelegInfos element is identical to the format of
   the SvcParams element defined in [RFC9460] Section 2.2, including the
   requirements for strictly increasing numeric order to keys and no key
   duplication allowed.




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   All the requirements in Section 2.2 of [RFC9460] apply.

   The DelegInfos element is a sequence of individual DelegInfo
   elements.  The wire format of an individual DelegInfo element is the
   same as for a SvcParam element, but it references DelegInfo elements
   instead of SvcParam elements.

                   +0 (MSB)                            +1 (LSB)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   0:  |                          DelegInfoKey                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   2:  |                length of DelegInfoValue                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   4:  /                          DelegInfoValue ...                   /
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The permissible lengths depend on the DelegInfoKey value.  Some
   future keys may have no DelegInfoValue, which would be indicated with
   an explicit 0 length.

2.3.  Overview of Differences between DELEG and DELEGI Semantics

   The following is a brief summary of semantic differences between the
   DELEG and DELEGI types.

   *  DELEG creates a delegation for its owner name, similar to the NS
      RR type.

   *  DELEG and NS RR types can coexist at the same owner name.

   *  DELEG is authoritative in the parent zone of the delegated zone,
      similar to the DS RR type, and unlike the NS RR type.

   *  DELEG is signed by the parent zone of the delegated zone when
      using DNSSEC, similar to the DS RR type, and unlike the NS RR
      type.

   *  DELEG cannot be present at the apex of the delegated zone, similar
      to the DS RR type, and unlike the NS RR type.

   *  DELEG has special processing for being included in answers.

   Conversely,

   *  DELEGI is like any normal RR and doesn't require any special
      processing.

   *  DELEGI does not create a delegation for its owner name.



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   *  DELEGI cannot coexist at the same owner name with DELEG or NS RR
      types.

   *  DELEGI DNSSEC signing and record placement rules are the same as
      for any ordinary RR type.

   *  DELEGI is used as the target of the DELEG protocol's "include"
      mechanism, as described in section Section 3.1.6.

   TODO: Add some introduction comparing how resolvers see legacy
   delegation (set of NS and A/AAAA records) and DELEG delegation (DELEG
   and DELEGI records with server-ipv4 and server-ipv6 keys)

3.  Use of DELEG Records

   The DELEG RRset MAY contain multiple records.  A DELEG RRset MAY be
   present with or without NS or DS RRsets at the delegation point,
   though without NS records then DELEG-unaware software will not be
   able to resolve records in the the delegated zone.

   DELEG RRsets MUST NOT appear at a zone's apex.  The erroneous
   inclusion of DELEG RRset at zone's apex will cause DNSSEC validation
   failures.  Servers MAY refuse to load such an invalid zone, similar
   to the DS RR type.

3.1.  Resolvers

3.1.1.  Signaling DELEG Support

   There will be both DELEG and NS needed for delegation for a long
   time.  Both legacy delegation and the DELEG protocol enable recursive
   resolution.  This document defines a new EDNS flag to signal that a
   resolver is DELEG-aware and therefore does not need NS records or
   glue information in a referral response.

   A resolver that is DELEG-aware MUST signal in queries that it
   supports the DELEG protocol by setting a bit in the OPT RR TTL as
   described in [RFC6891].  This bit referred to as the "DELEG" (DE)
   bit, expected to be assigned by IANA at Bit 2 in the EDNS Header
   Flags registry, as follows:

               +0 (MSB)                +1 (LSB)
        +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     0: |   EXTENDED-RCODE      |       VERSION         |
        +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     2: |DO|CO|DE|              Z                       |
        +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+




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   Setting the DE bit to one in a query indicates the resolver
   understands the DELEG semantics and does not need NS records to
   follow a referral.  The DE bit set to 0 indicates the resolver is not
   DELEG-aware, and therefore can only be served referrals with NS
   records and other data according to pre-DELEG specifications.

3.1.2.  Referral

   The DELEG record creates a zone cut similar to the NS record.

   If one or more DELEG records exist at a given delegation point, a
   DELEG-aware resolver MUST treat the name servers from those DELEG
   records as authoritative for the child zone.  In such a case, a
   DELEG-aware resolver MUST NOT use NS records for the zone if they are
   present, even if resolution using DELEG records has failed.  Such
   fallback from DELEG to NS would invalidate the security guarantees of
   the DELEG protocol.

   If no DELEG record exists at a given delegation point, DELEG-aware
   resolvers MUST use NS records as specified by [RFC1034].  See
   Section 3.4 for more information about protection from downgrade
   attacks.

3.1.3.  Parent-side types, QTYPE=DELEG

   Record types defined as authoritative on the parent side of zone cut,
   currently the DS and DELEG types, retain the same special handling as
   described in Section 2.6 of [RFC4035].

   DELEG-unaware resolvers can get different types of answers for
   QTYPE=DELEG queries based on the configuration of the server, such as
   whether it is DELEG-aware and whether it also is authoritative for
   subdomains.  For example, a DELEG-unaware authoritative name server
   which has loaded DELEG records via the [RFC3597] unknown types
   mechanism would answer with them only if there were no NS records at
   the owner name, and answer with an NS delegation otherwise.

3.1.4.  Algorithm for "Finding the Best Servers to Ask"

   This document updates instructions for finding the best servers to
   ask.  That information currently is covered in Section 5.3.3 of
   [RFC1034] and Section 3.4.1 of [RFC6672] with the text "2.  Find the
   best servers to ask."  Section 3.1.4.1 of [RFC4035] should have
   explicitly updated Section 5.3.3 of [RFC1034] for the DS RR type, but
   failed to do so.  This document simply extends this existing behavior
   to DELEG RR type as well, and makes this special case explicit.





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   When a DELEG RRset exists for a delegation in a zone, DELEG-aware
   resolvers ignore any NS RRset for the delegated zone, whether from
   the parent or from the apex of the child.

   Each delegation level can have a mixture of DELEG and NS RR types,
   and DELEG-aware resolvers MUST be able to follow chains of
   delegations which combines both types in arbitrary ways.

   An example of a valid delegation tree:

   ; root zone with NS-only delegations
   . SOA ...
   test. NS ...

   ; test. zone with NS+DELEG delegations
   test. SOA ...
   sld.test. NS ...
   sld.test. DELEG ...

   ; sld.test. zone with NS-only delegation
   sld.test. SOA ...
   nssub.sld.test. NS ...

   ; nssub.sld.test. zone with DELEG-only delegation
   delegsub.sub.sld.test. DELEG ...

   TODO: after the text below, refer back to this figure and show the
   order that a DELEG-aware resolver would take when there is a failure
   to find any good DELEG addresses at sub.sld.test, then any usable
   name servers at sub.sld.test, and then maybe a good DELEG record at
   test.

   The terms SNAME and SLIST used here are defined in Section 5.3.2 of
   [RFC1034]:

   SNAME is the domain name we are searching for.

   SLIST is a structure which describes the name servers and the zone
   which the resolver is currently trying to query.  Neither [RFC1034]
   nor this document define how a resolver uses SLIST; they only define
   how to populate it.










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   A DELEG-aware SLIST needs to be able to hold two types of
   information, delegations defined by NS records and delegations
   defined by DELEG records.  DELEG and NS delegations can create cyclic
   dependencies and/or lead to duplicate entries which point to the same
   server.  Resolvers need to enforce suitable limits to prevent damage
   even if someone has incorrectly configured some of the data used to
   create an SLIST.

   This leads to a modifications of the description from earlier
   documents for DELEG-aware resolvers can find the best servers to ask.
   That description becomes:

   1.  Determine deepest possible zone cut which can potentially hold
       the answer for a given (query name, type, class) combination:

       1.  Start with SNAME equal to QNAME.

       2.  If QTYPE is a type that is authoritative at the parent side
           of a zone cut (currently, DS or DELEG), remove the leftmost
           label from SNAME.  For example, if the QNAME is
           "test.example." and the QTYPE is DELEG or DS, set SNAME to
           "example.".

   2.  Look for locally-available DELEG and NS RRsets, starting at
       current SNAME.

       1.  For a given SNAME, check for the existence of a DELEG RRset.
           If it exists, the resolver MUST use its content to populate
           SLIST.  However, if the DELEG RRset is known to exist but is
           unusable (for example, if it is found in DNSSEC BAD cache),
           the resolver MUST NOT instead use an NS RRset; instead, the
           resolver MUST treat this case as if no servers were
           available.

       2.  If a given SNAME is proven to not have a DELEG RRset but does
           have an NS RRset, the resolver MUST copy the NS RRset into
           SLIST.

       3.  If SLIST is now populated, stop walking up the DNS tree.
           However, if SLIST is not populated, remove the leftmost label
           from SNAME and go back to the first step, using the newly
           shortened SNAME.  Do not go back to the first step if doing
           so would exceed the amount of work that the resolver is
           configured to do when processing names; see Section 4.1.

   The rest of Step 2's description is not affected by this document.





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   Resolvers MAY respond to "QNAME=. / QTYPE=DELEG" queries in the same
   fashion as they respond to "QNAME=. / QTYPE=DS" queries.

3.1.5.  Name Server Information for Delegation

   The DELEG and DELEGI records have four keys that describe information
   about name servers.  The purpose of this information is to populate
   the SLIST with IP addresses of the name servers for a zone.  The
   types of information defined in this document are:

   *  server-ipv4: an unordered collection of IPv4 addresses for name
      servers

   *  server-ipv6: an unordered collection of IPv6 addresses for name
      servers

   *  server-name: an unordered collection of hostnames of name servers;
      the addresses must be fetched

   *  include-delegi: an unordered collection of domain names that point
      to a DELEGI RRsets, which in turn have more information about the
      delegation

   These keys MUST have a non-empty DelegInfoValue.

   The presentation values for server-ipv4 and server-ipv6 are comma-
   separated list of one or more IP addresses of the appropriate family
   in standard textual format [RFC5952] [RFC4001].  The wire formats for
   server-ipv4 and server-ipv6 are a sequence of IP addresses, in
   network byte order, for the respective address family.

   The presentation values for server-name and include-delegi are an
   unordered collection of fully-qualified domain names and relative
   domain names, separated by commas.  The wire format for server-name
   and include-delegi are each a concatenated set of a wire-format
   domain names, where the root label provides the separation between
   names.  The names in the wire format MUST NOT be compressed.

   TODO: Describe how escaping works for server-name and include-delegi.
   This will be the same as the escaping mechanism defined in SVCB.

   A DELEG or DELEGI record that has a non-empty DelegInfos MUST have
   one, and only one, set of server information, chosen from the
   following:

   *  one server-ipv4 key

   *  one server-ipv6 key



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   *  a pair consisting of one server-ipv4 key and one server-ipv6 key

   *  one server-name key

   *  one include-delegi key

   This restriction only applies to a single DELEG or DELEGI record; a
   DELEG or DELEGI RRset can have records with different server
   information keys.

   When using server-name, the addresses for all the names in the set
   must be fetched using normal DNS resolution.  This means the names in
   the value of the server-name key or the include-delegi key MUST NOT
   be inside the delegated domain.

   With this initial DELEG specification, servers are still expected to
   be reached on the standard DNS port for both UDP and TCP, 53.  While
   a future specification is expected to address other transports using
   other ports, its eventual semantics are not covered here.

3.1.6.  Populating the SLIST from DELEG and DELEGI Records

   Each individual DELEG record inside a DELEG RRset, or each individual
   DELEGI record in a DELEGI RRset, can cause the addition of zero or
   more entries to SLIST.

   A resolver processes each individual DELEG record within a DELEG
   RRset, or each individual DELEGI record in a DELEGI RRset, using the
   following steps:

   1.  If a record has more than one type of server information key
       (excluding the IPv4/IPV6 case), or has multiple server
       information keys of the same type, that record is malformed.
       Stop processing this record.

   2.  If server-ipv4 and/or server-ipv6 keys are present inside the
       record, copy all of the address values into SLIST.  Stop
       processing this record.

   3.  If a server-name key is present in the record, resolve each name
       in the value into IPv4 and/or IPv6 addresses.  Copy these
       addresses into SLIST.  Stop processing this record.

   4.  If an include-delegi key is present in the record, resolve each
       name in the value using the DELEGI RR type.  Recursively apply
       the algorithm described in this section, after checking that the
       maximum loop count described in Section 4.1 has not been reached.




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   5.  If none of the above applies, SLIST is not modified by this
       particular record.

   A DELEG-aware resolver MAY implement lazy filling of SLIST, such as
   by deferring processing remaining records if SLIST already has what
   the resolver considers a sufficiently large pool of addresses to
   contact.

   The order in which to try the servers in the final SLIST is outside
   the scope of this document.

3.2.  Authoritative Servers

   The DELEG RR type defines a zone cut in similar way as the NS RR
   type.  Behavior defined for zone cuts in existing pre-DELEG
   specifications apply to zone cuts created by the DELEG record.  A
   notable example of this is that the occlusion (usually accidentally)
   created by NS records in a parent zone would also be created by DELEG
   records in a parent zone.

   DELEG-aware authoritative servers act differently when handling
   queries from DELEG-unaware clients (those with DE=0) than from DELEG-
   aware clients (those with DE=1).

   The server MUST copy the value of the DE bit from the query into the
   response, to signal that it is a DELEG-aware server.

3.2.1.  DELEG-aware Clients

   When the client indicates that it is DELEG-aware by setting DE=1 in
   the query, DELEG-aware authoritative servers treat DELEG records as
   zone cuts, and the servers are authoritative on the parent side of
   the zone cut.  This new zone cut has priority over a legacy
   delegation.

3.2.1.1.  DELEG-aware Clients Requesting QTYPE=DELEG

   An explicit query for the DELEG RR type at a delegation point behaves
   much like query for the DS RR type: the server answers
   authoritatively from the parent zone.  All pre-DELEG specifications
   for special handling queries with QTYPE=DS apply equally to
   QTYPE=DELEG.  In summary, the server either provides an authoritative
   DELEG RRset or declares its non-existence, with relevant DNSSEC
   proofs when requested and available.







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3.2.1.2.  Delegation with DELEG

   If the delegation has a DELEG RRset, the authoritative server MUST
   put the DELEG RRset into the Authority section of the referral.  In
   this case, the server MUST NOT include the NS RRset in the Authority
   section.  Include the covering RRSIG following the normal DNSSEC
   procedure for answers with authoritative zone data.

   Similarly, rules for DS RRset inclusion in referrals apply as
   specified by the DNSSEC protocol.

3.2.1.3.  DELEG-aware Clients with NS RRs Present but No DELEG RRs

   If the delegation does not have a DELEG RRset, the authoritative
   server MUST put the NS RRset into the authority section of the
   referral.  The absence of the DELEG RRset MUST be proven as specified
   by the DNSSEC protocol for authoritative data.

   Similarly, rules for DS RRset inclusion into referrals apply as
   specified by the DNSSEC protocol.  Please note, in practice the same
   process and records are used to prove the non-existence of both DELEG
   and DS RRsets.

3.2.2.  DELEG-unaware Clients

   A general principle for DELEG-aware authoritative servers is that
   they respond to a DELEG-unaware client by following pre-DELEG
   specifications.

   DELEG-unaware clients do not recognize DELEG records as a zone cut
   and are not aware of the special handling rules for DELEG records.
   They understand a DELEG RRset as an ordinary unknown RR type.

   In summary, DELEG records are not returned in referral responses to
   DELEG-unaware clients, and DELEG-unaware clients do not consider
   DELEG records authoritative on the parent side of a zone cut.

   An authoritative server responding to DELEG-unaware clients has to
   handle three distinct situations:

   *  No DELEG RRset is present.  In this case, the authoritative server
      follows the pre-DELEG specifications.

   *  An NS RRset and a DELEG RRset are both present.  In this case, the
      authoritative server uses the NS RRset when constructing referral
      responses, following the pre-DELEG specifications.  See also
      Section 3.3 and Appendix A.




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   *  A DELEG RRset is present, but an NS RRset is not.  See
      Section 3.2.2.1.

3.2.2.1.  DELEG-unaware Clients with DELEG RRs Present but No NS RRs

   Authoritative servers may receive requests from DELEG-unaware clients
   for which the child zone is authoritative and is delegated with DELEG
   RRs only (that is, without any NS RRs).  Such a zone is by definition
   not resolvable for DELEG-unaware clients.  From the perspective of a
   DELEG-unaware client, the zone cut created by the DELEG RRs is
   invisible.  In such a situation, the authoritative server should
   respnd in a way to limit confusion and/or colateral damage for the
   DELEG-unaware client.

   The authoritative server is RECOMMENDED to supplement its responses
   to DELEG-unaware resolvers with an [RFC8914] Extended DNS Error using
   the (IANA-TBD) value "New Delegation Only" from the Extended DNS
   Error Codes registry.

   A DELEG-aware authoritative server implementation has two options:

   1.  When faced with a client that sent a query with DE=0 that would
       lead to a delegation, but the zone has no NS records, an
       authoritative server MAY reply with an RCODE of SERVFAIL and
       nothing in the Answer and Authority sections.

       This response has negative side effects, namely that most
       resolvers will then query the remaining authoritative servers to
       see if any of them would give a different answer.  The advantage
       of this approach is simplicity of implementation and it is easy
       to understand.

   2.  Because of the negative side effects of the previous option, an
       authoritative server SHOULD instead send an answer that
       accurately describes the situation to a DELEG-unaware resolver.

       The NSEC chain and the type bitmap generated according to
       Section 3.3 leads to exactly one possible answer which is valid
       according to pre-DELEG specifications.  See Appendix A for
       several examples of such answers.

       Please note different interpretation of DELEG RR type and zone
       cut definitions between DELEG-aware authoritative server and
       DELEG-unaware client.  It is confusing.







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   TODO: List as many of the possible situations that need to be
   considered for variant 2, and the proposed the single appropriate
   response for each situation.  This list will probably change for the
   next few iterations of this draft.

3.2.2.2.  DELEG-unaware Clients Requesting QTYPE=DELEG

   From the perspective of DELEG-unaware clients, the DELEG RR type does
   not have special semantics and should behave like an old ordinary RR
   type such as TXT.  Thus, queries with DE=0 and QTYPE=DELEG MUST
   result in a legacy response which can be validated by DELEG-unaware
   client.

   *  If there is an NS RRset, this will be a legacy referral to the
      child zone.  From the perspective of a DELEG-unaware client, the
      DELEG RR is effectively occluded by NS RRset.  The DELEG-unaware
      resolver can then obtain a final answer which can be validated
      from the child zone in similar fashion as described in [RFC4035]
      section 3.1.4.1.

   *  If there is no NS RRset but there is a DELEG RRset, this will be a
      normal authoritative response with the DELEG RRset, following pre-
      DELEG specifications.

   *  If there is no NS RRset and no DELEG RRset, this will be a
      standard negative response following pre-DELEG specifications.

   TODO: Should we have an example with auth having parent+child zone at
   the same time, and DE=0 QTYPE=DELEG query?

3.3.  DNSSEC Signers

   The DELEG record is authoritative on the parent side of a zone cut
   and needs to be signed as such.  Existing rules from the DNSSEC
   specifications apply.

   In summary: for DNSSEC signing, treat the DELEG RR type the same way
   as the DS RR type.

   DELEG RR type defines a zone cut in similar way as NS RR type.  This
   has several consequences which stem from existing pre-DELEG
   specifications:

   *  All owner names below zone cut are occluded and thus not present
      in NSEC chains.






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   *  All RRsets which are not permissible at the parent side of zone
      cut are occluded too and not represented in NSEC chain type
      bitmap.

   See examples in Appendix A.1 and Appendix A.4.2.3.

   In order to protect validators from downgrade attacks this draft
   introduces a new DNSKEY flag ADT (Authoritative Delegation Types).
   In zones which contain a DELEG RRset, this flag MUST be set to 1 in
   at least one of the DNSKEY records published in the zone.

3.4.  DNSSEC Validators

   DELEG awareness introduces additional requirements on validators.

3.4.1.  Clarifications on Nonexistence Proofs

   This document updates Section 4.1 of [RFC6840] to include "NS or
   DELEG" types in the type bitmap as indication of a delegation point,
   and generalizes applicability of ancestor delegation proof to all RR
   types that are authoritative at the parent (that is, both DS and
   DELEG).  The text in that section is updated as follows:

   An "ancestor delegation" NSEC RR (or NSEC3 RR) is one with:

   *  the NS and/or DELEG bit set,

   *  the Start of Authority (SOA) bit clear, and

   *  a signer field that is shorter than the owner name of the NSEC RR,
      or the original owner name for the NSEC3 RR.

   Ancestor delegation NSEC or NSEC3 RRs MUST NOT be used to assume
   nonexistence of any RRs below that zone cut, which include all RRs at
   that (original) owner name, other than types authoritative at the
   parent-side of a zone cut (DS and DELEG), and all RRs below that
   owner name regardless of type.

3.4.2.  Insecure Delegation Proofs

   This document updates Section 4.4 of [RFC6840] to include securing
   DELEG records, and explicitly states that Opt-Out is not applicable
   to the DELEG protocol.  The first paragraph of that section is
   updated to read:

   Section 5.2 of [RFC4035] specifies that a validator, when proving a
   delegation is not secure, needs to check for the absence of the DS
   and SOA bits in the NSEC (or NSEC3) type bitmap; this was clarified



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   in Section 4.1 of [RFC6840].  This document updates [RFC4035] and
   [RFC6840] to specify that the validator MUST also check for the
   presence of the NS or the DELEG bit in the matching NSEC (or NSEC3)
   RR (proving that there is, indeed, a delegation).  Alternately, the
   validator must make sure that the delegation with an NS record is
   covered by an NSEC3 RR with the Opt-Out flag set.  Opt-Out is not
   applicable to DELEG RR type because DELEG records are authoritative
   at the parent side of a zone cut in the same way that DS RR types
   are.

3.4.3.  Referral downgrade protection

   If the zone is DNSSEC-secure, and if any DNSKEY of the zone has the
   ADT flag set to 1, a DELEG-aware validator MUST prove the absence of
   a DELEG RRset in referral responses from this particular zone.

   Without this check, an attacker could strip the DELEG RRset from a
   referral response and replace it with an unsigned (and potentially
   malicious) NS RRset.  A referral response with an unsigned NS and
   signed DS RRsets does not require additional proofs of nonexistence
   according to pre-DELEG DNSSEC specification, and it would have been
   accepted as a delegation without the DELEG RRset.

3.4.4.  Chaining

   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,
   that forwarder has to be security-aware and DELEG-aware as well.

4.  Security Considerations

   TODO: Add more here

4.1.  Preventing Over-work Attacks

   Resolvers MUST prevent situations where accidental misconfiguration
   of zones or malicious attacks cause them to perform too much work
   when resolving.  This document describes two sets of actions that, if
   not controlled, could lead to over-work attacks.

   Long chains of include-delegi information (Section 3.1.5), and those
   with circular chains of include-delegi information, can be
   burdensome.  To prevent this, the resolver SHOULD NOT follow more
   than 3 include-delegi chains in an RRset when populating SLIST.  Note
   that include-delegi chains can have CNAME steps in them; in such a
   case, a CNAME step is counted the same as a DELEGI step when
   determining when to stop following a chain.




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4.2.  Preventing Downgrade Attacks

   TODO: this section is a bit redundant with "Referral Downgrade
   Protection" above; harmonize them.

   During the rollout of the DELEG protocol, the operator of an
   authoritative server can upgrade the server software to be DELEG-
   aware before changing any DNS zones.  Such deployment should work and
   provide DELEG-aware clients with correct DELEG-aware answers.
   However, the deployment will not be protected from downgrade attacks
   against the DELEG protocol.

   To protect DNSSEC-secure DNS zones that use DELEG delegations, the
   delegating zone needs to have at least one DNSKEY with the ADT flag
   set to 1.  Failure to set this flag in a DNSKEY record in the zone
   allows an attacker to remove the DELEG RRset from referrals which
   contain the DS RRset, and replace the original signed DELEG RRset
   with an arbitrary unsigned NS set.  Doing so would be a downgrade
   from the strong protection offered by DNSSEC for DELEG.  That is, the
   DELEG protocol when used with upgraded DNSKEY records gives the same
   protection to DELEG that the zone's DS RR set has.  Without DELEG,
   there are no security guarantees for the NS RR set on the parent side
   of the zone cut.

   Please note that a full DNSKEY rollover is not necessary to achieve
   the downgrade protection for DELEG.  Any single DNSKEY with the ADT
   flag set to 1 is sufficient; the zone can introduce an otherwise
   unused record into the DNSKEY RRset.  This DNSKEY RR can even use an
   unknown signing algorithm and zero-length key material to minimize
   size increase of the DNSKEY RRset.

5.  IANA Considerations

5.1.  Changes to Existing Registries

   IANA is requested to allocate the DELEG RR and the DELEGI RR in the
   Resource Record (RR) TYPEs registry, with the meaning "enhanced
   delegation information" and referencing this document.

   IANA is requested to assign a new bit in the DNSKEY RR Flags registry
   ([RFC4034]) for the ADT bit (N), with the description "Authoritative
   Delegation Types" and referencing this document.  For compatibility
   reasons, we request the bit 14 to be used.  This value has been
   proven to work whereas bit 0 was proven to break in practical
   deployments (because of bugs).






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   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.

   IANA is requested to assign a value from the Extended DNS Error Codes
   ([RFC8914]), with the Purpose "New Delegation Only" and referencing
   this document.

5.2.  New Registry for Delegation Information

   IANA is requested to create the "DELEG Delegation Information"
   registry.  This registry defines the namespace for delegation
   information keys, including string representations and numeric key
   values.

5.2.1.  Procedure

   A registration MUST include the following fields:

   Number: Wire-format numeric identifier (range 0-65535) Name: Unique
   presentation name Meaning: A short description Reference: Location of
   specification or registration source Change Controller: Person or
   entity, with contact information if appropriate

   To enable code reuse from SVCB parsers, the requirements for
   registered Name exactly copy requirements set by [RFC9460] section
   14.3.1: The characters in the registered Name field entry MUST be
   lowercase alphanumeric or "-".  The name MUST NOT start with "key" or
   "invalid".

   The registration policy for new entries is Expert Review ([RFC8126]).
   The designated expert MUST ensure that the reference is stable and
   publicly available and that it specifies how to convert the
   delegation information's presentation format to wire format.  The
   reference MAY be any individual's Internet-Draft or a document from
   any other source with similar assurances of stability and
   availability.  An entry MAY specify a reference of the form "Same as
   (other key name)" if it uses the same presentation and wire formats
   as an existing key.

   This arrangement supports the development of new parameters while
   ensuring that zone files can be made interoperable.

5.2.2.  Initial Contents

   The "DELEG Delegation Information" registry should be populated with
   the following initial registrations:




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   Number:  1
   Name:  server-ipv4
   Meaning:  An unordered collection of IPv4 addresses of name servers
   Reference:  {{nameserver-info}} of this document
   Change Controller:  IETF

   Number:  2
   Name:  server-ipv6
   Meaning:  An unordered collection of IPv6 addresses of name servers
   Reference:  {{nameserver-info}} of this document
   Change Controller:  IETF

   Number:  3
   Name:  server-name
   Meaning:  An unordered collection of hostnames of name servers
   Reference:  {{nameserver-info}} of this document
   Change Controller:  IETF

   Number:  4
   Name:  include-delegi
   Meaning:  An unordered collection of domain names of DELEGI records
   Reference:  {{nameserver-info}} of this document
   Change Controller:  IETF

   The registration for numbers 65280-65534 is reserved for private use.
   The registration for number 65535 is reserved.

5.3.  Temporary Assignments

   This section gives the values that can be used for interoperability
   testing before IANA makes permanent assignments.  The section will be
   removed when IANA makes permanent assignments.

   *  DELEG RR type code is 61440

   *  DELEGI RR type code is 65433

   *  DELEG EDNS DE flag bit is 2

   *  DNSKEY ADT (Authoritative Delegation Types) flag bit is 14

6.  References

6.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/rfc/rfc1034>.



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   [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,
              <https://www.rfc-editor.org/rfc/rfc4034>.

   [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,
              <https://www.rfc-editor.org/rfc/rfc4035>.

   [RFC6672]  Rose, S. and W. Wijngaards, "DNAME Redirection in the
              DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
              <https://www.rfc-editor.org/rfc/rfc6672>.

   [RFC6840]  Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
              Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
              DOI 10.17487/RFC6840, February 2013,
              <https://www.rfc-editor.org/rfc/rfc6840>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/rfc/rfc6891>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/rfc/rfc8126>.

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/rfc/rfc8914>.

   [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, <https://www.rfc-editor.org/rfc/rfc9460>.

6.2.  Informative References

   [BCP219]   Best Current Practice 219,
              <https://www.rfc-editor.org/info/bcp219>.
              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,
              <https://www.rfc-editor.org/info/rfc9499>.



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   [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,
              <https://datatracker.ietf.org/doc/html/draft-tapril-
              ns2-01>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record
              (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
              2003, <https://www.rfc-editor.org/rfc/rfc3597>.

   [RFC4001]  Daniele, M., Haberman, B., Routhier, S., and J.
              Schoenwaelder, "Textual Conventions for Internet Network
              Addresses", RFC 4001, DOI 10.17487/RFC4001, February 2005,
              <https://www.rfc-editor.org/rfc/rfc4001>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <https://www.rfc-editor.org/rfc/rfc5952>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

Appendix A.  Examples

A.1.  Root zone file

   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.

   TODO: Add examples that have server-name and include-delegi being
   sets of more than one name.

   TODO: Examples that show DELEGI records in ns2.example.net and
   ns3.example.org.






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   example.   DELEG server-ipv4=192.0.2.1 server-ipv6=2001:DB8::1
   example.   DELEG server-name=ns2.example.net.,ns3.example.org.
   example.   RRSIG DELEG 13 1 300 20260101000000 (
                           20250101000000 33333 . SigExampleDELEG/ )

   example.   NS    a.example.
   example.   NS    b.example.net.
   example.   NS    c.example.org.

   example.   DS    44444 13 2 ABCDEF01234567...
   example.   RRSIG DS 13 1 300 20260101000000 (
                           20250101000000 33333 . SigExampleDS )

   example.   NSEC  net. NS DS RRSIG NSEC DELEG
   example.   RRSIG NSEC 13 1 300 20260101000000 (
                           20250101000000 33333 . SigExampleNSEC+/ )

   ; unsigned glue for legacy (NS) delegation
   ; it is NOT present in NSEC chain
   a.example. A     192.0.2.1
   a.example. AAAA  2001:DB8::1

   The "test." delegation point has a DELEG record and no NS or DS
   records.

   Please note: This is an example of unnecessarily complicated setup to
   demonstrate capabilities of DELEG and DELEGI RR types.

   test.      DELEG server-ipv6=3fff::33
   test.      DELEG include-delegi=Acfg.example.org.
   test.      DELEG include-delegi=config2.example.net.
   test.      RRSIG DELEG 13 1 300 20260101000000 (
                           20250101000000 33333 . SigTestDELEG )

   test.      NSEC  . RRSIG NSEC DELEG
   test.      RRSIG NSEC 13 1 300 20260101000000 (
                           20250101000000 33333 . SigTestNSEC/ )

   ; a forgotten glue from legacy (NS) delegation
   ; it is NOT present in NSEC chain and it is occluded
   a.test.    A     192.0.2.1

   Delegations to org and net zones omitted for brevity.

A.2.  Example.org zone file

   The following example shows an excerpt from an unsigned example.org
   zone.



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 Acfg.example.org.    DELEGI server-ipv6=2001:DB8::6666
 Acfg.example.org.    DELEGI server-name=c.example.org.
 Acfg.example.org.    DELEGI include-delegi=subcfg.example.org.

 c.example.org.       AAAA   3fff::33

 subcfg.example.org.  DELEGI server-ipv4=203.0.113.1 server-ipv6=3fff::2

A.3.  Example.net zone file

   The following example shows an excerpt from an unsigned example.net
   zone.

   b.example.net.       A      198.51.100.1

   config2.example.net. DELEGI server-name=b.example.org.

A.4.  Responses

   The following sections show referral examples:

A.4.1.  DO bit clear, DE bit clear

A.4.1.1.  Query for foo.example

   ;; Header: QR RCODE=NOERROR
   ;;

   ;; Question
   foo.example.  IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   example.   NS    a.example.
   example.   NS    b.example.net.
   example.   NS    c.example.org.

   ;; Additional
   a.example. A     192.0.2.1
   a.example. AAAA  2001:DB8::1

A.4.1.2.  Query for foo.test







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   ;; Header: QR AA RCODE=NXDOMAIN
   ;;

   ;; Question
   foo.test.   IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   .   SOA ...

   ;; Additional
   ;; OPT with Extended DNS Error: New Delegation Only

A.4.1.3.  Query for a.test

   A forgotten glue record under the "test." delegation point is
   occluded by DELEG RRset.

   ;; Header: QR AA RCODE=NXDOMAIN
   ;;

   ;; Question
   a.test.   IN A

   ;; Answer
   ;; (empty)

   ;; Authority
   .   SOA ...

   ;; Additional
   ;; OPT with Extended DNS Error: New Delegation Only

A.4.2.  DO bit set, DE bit clear

A.4.2.1.  Query for foo.example













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   ;; Header: QR DO RCODE=NOERROR
   ;;

   ;; Question
   foo.example.   IN MX

   ;; Answer
   ;; (empty)

   ;; Authority

   example.   NS    a.example.
   example.   NS    b.example.net.
   example.   NS    c.example.org.
   example.   DS    44444 13 2 ABCDEF01234567...
   example.   RRSIG DS 13 1 300 20260101000000 (
                           20250101000000 33333 . SigExampleDS )
   ;; Additional
   a.example. A     192.0.2.1
   a.example. AAAA  2001:DB8::1

A.4.2.2.  Query for foo.test

   ;; Header: QR DO AA RCODE=NXDOMAIN
   ;;

   ;; Question
   foo.test.      IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   .          SOA ...
   .          RRSIG SOA ...
   test.      NSEC  . RRSIG NSEC DELEG
   test.      RRSIG NSEC 13 1 300 20260101000000 (
                           20250101000000 33333 . SigTestNSEC/ )

   ;; Additional
   ;; OPT with Extended DNS Error: New Delegation Only

A.4.2.3.  Query for a.test

   A forgotten glue record under the "test." delegation point is
   occluded by DELEG RRset.  This is indicated by NSEC chain which
   "skips" over the owner name with A RRset.




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   ;; Header: QR DO AA RCODE=NXDOMAIN
   ;;

   ;; Question
   a.test.      IN A

   ;; Answer
   ;; (empty)

   ;; Authority
   .          SOA ...
   .          RRSIG SOA ...
   test.      NSEC  . RRSIG NSEC DELEG
   test.      RRSIG NSEC 13 1 300 20260101000000 (
                           20250101000000 33333 . SigTestNSEC/ )

   ;; Additional
   ;; OPT with Extended DNS Error: New Delegation Only

A.4.3.  DO bit clear, DE bit set

A.4.3.1.  Query for foo.example

   ;; Header: QR DE RCODE=NOERROR
   ;;

   ;; Question
   foo.example.  IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   example.   DELEG server-ipv4=192.0.2.1 server-ipv6=2001:DB8::1
   example.   DELEG server-name=ns2.example.net.,ns3.example.org.

   ;; Additional
   ;; (empty)

A.4.3.2.  Query for foo.test











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   ;; Header: QR AA RCODE=NOERROR
   ;;

   ;; Question
   foo.test.   IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   test.      DELEG server-ipv6=3fff::33
   test.      DELEG include-delegi=Acfg.example.org.
   test.      DELEG include-delegi=config2.example.net.

   ;; Additional
   ;; (empty)

   Follow-up example in Appendix A.5 explains ultimate meaning of this
   response.

A.4.4.  DO bit set, DE bit set

A.4.4.1.  Query for foo.example

   ;; Header: QR DO DE RCODE=NOERROR
   ;;

   ;; Question
   foo.example.  IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   example.   DELEG server-ipv4=192.0.2.1 server-ipv6=2001:DB8::1
   example.   DELEG server-name=ns2.example.net.,ns3.example.org.
   example.   RRSIG DELEG 13 1 300 20260101000000 (
                           20250101000000 33333 . SigExampleDELEG/ )
   example.   DS    44444 13 2 ABCDEF01234567...
   example.   RRSIG DS 13 1 300 20260101000000 (
                           20250101000000 33333 . SigExampleDS )

   ;; Additional
   a.example. A     192.0.2.1
   a.example. AAAA  2001:DB8::1

A.4.4.2.  Query for foo.test




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   ;; Header: QR DO DE AA RCODE=NOERROR
   ;;

   ;; Question
   foo.test.      IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   test.      DELEG server-ipv6=3fff::33
   test.      DELEG include-delegi=Acfg.example.org.
   test.      DELEG include-delegi=config2.example.net.
   test.      RRSIG DELEG 13 1 300 20260101000000 (
                           20250101000000 33333 . SigTestDELEG )
   test.      NSEC  . RRSIG NSEC DELEG
   test.      RRSIG NSEC 13 1 300 20260101000000 (
                           20250101000000 33333 . SigTestNSEC/ )

   ;; Additional
   ;; (empty)

   Follow-up example in Appendix A.5 explains the ultimate meaning of
   this response.

A.5.  DELEGI Interpretation

   In the examples above, the test.  DELEG record uses indirection and
   points to other domain names with DELEGI, A, and AAAA records.
   During resolution, a resolver will gradually build set of name
   servers to contact, as defined in Section 3.1.6.

   To visualize end result of this process we represent full set of name
   servers in form of a 'virtual' DELEG RRset.

test. DELEG server-ipv4=198.51.100.1
test. DELEG server-ipv4=203.0.113.1
test. DELEG server-ipv6=2001:DB8::6666
test. DELEG server-ipv6=3fff::2
; IPv6 address 3fff::33 was de-duplicated (input RRsets listed it twice)
test. DELEG server-ipv6=3fff::33

   Implementations are free to use arbitrary representation for this
   data as it is not directly exposed via DNS protocol.







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Acknowledgments

   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.

   Work on DELEG protocol has started at IETF 118 Hackaton.  Hackaton
   participants: Christian Elmerot, David Blacka, David Lawrence, Edward
   Lewis, Erik Nygren, George Michaelson, Jan Včelák, Klaus Darilion,
   Libor Peltan, Manu Bretelle, Peter van Dijk, Petr Špaček, Philip
   Homburg, Ralf Weber, Roy Arends, Shane Kerr, Shumon Huque, Vandan
   Adhvaryu, Vladimír Čunát, Andreas Schulze.

   Other people joined the effort after the initial hackaton: Ben
   Schwartz, Bob Halley, Paul Hoffman, Miek Gieben ...

Authors' Addresses

   Tim April
   Google, LLC
   Email: ietf@tapril.net


   Petr Špaček
   ISC
   Email: pspacek@isc.org


   Ralf Weber
   Akamai Technologies
   Email: rweber@akamai.com


   David C Lawrence
   Salesforce
   Email: tale@dd.org













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