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DNS Catalog Zones

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9432.
Authors Peter van Dijk , Libor Peltan , Ondřej Surý , Willem Toorop , Kees Monshouwer , Peter Thomassen , Aram Sargsyan
Last updated 2023-07-06 (Latest revision 2023-02-07)
Replaces draft-toorop-dnsop-dns-catalog-zones
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Tim Wicinski
Shepherd write-up Show Last changed 2022-10-13
IESG IESG state Became RFC 9432 (Proposed Standard)
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Consensus boilerplate Yes
Telechat date (None)
Responsible AD Warren "Ace" Kumari
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IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
DNSOP Working Group                                          P. van Dijk
Internet-Draft                                                  PowerDNS
Intended status: Standards Track                               L. Peltan
Expires: 11 August 2023                                           CZ.NIC
                                                                 O. Sury
                                             Internet Systems Consortium
                                                               W. Toorop
                                                              NLnet Labs
                                                         C.R. Monshouwer
                                                            P. Thomassen
                                 deSEC, SSE - Secure Systems Engineering
                                                             A. Sargsyan
                                             Internet Systems Consortium
                                                         7 February 2023

                           DNS Catalog Zones


   This document describes a method for automatic DNS zone provisioning
   among DNS primary and secondary nameservers by storing and
   transferring the catalog of zones to be provisioned as one or more
   regular DNS zones.

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

   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 11 August 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Catalog Zone Structure  . . . . . . . . . . . . . . . . . . .   4
     4.1.  Member Zones  . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Properties  . . . . . . . . . . . . . . . . . . . . . . .   5
       4.2.1.  Schema Version (version property) . . . . . . . . . .   6
     4.3.  Member Zone Properties  . . . . . . . . . . . . . . . . .   7
       4.3.1.  Change of Ownership (coo property)  . . . . . . . . .   7
       4.3.2.  Groups (group property) . . . . . . . . . . . . . . .   8
     4.4.  Custom Properties (*.ext properties)  . . . . . . . . . .   9
   5.  Nameserver Behavior . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  General Requirements  . . . . . . . . . . . . . . . . . .  10
     5.2.  Member zone name clash  . . . . . . . . . . . . . . . . .  11
     5.3.  Member zone removal . . . . . . . . . . . . . . . . . . .  11
     5.4.  Member node name change . . . . . . . . . . . . . . . . .  11
     5.5.  Migrating member zones between catalogs . . . . . . . . .  11
     5.6.  Zone-associated state reset . . . . . . . . . . . . . . .  12
   6.  Implementation and Operational Notes  . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  16
   11. Informative References  . . . . . . . . . . . . . . . . . . .  17
   Appendix A.  Catalog Zone Example . . . . . . . . . . . . . . . .  17
   Appendix B.  Implementation Status  . . . . . . . . . . . . . . .  18
   Appendix C.  Change History . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   The content of a DNS zone is synchronized among its primary and
   secondary nameservers using AXFR and IXFR.  However, the list of
   zones served by the primary (called a catalog in [RFC1035]) is not
   automatically synchronized with the secondaries.  To add or remove a
   zone, the administrator of a DNS nameserver farm not only has to add
   or remove the zone from the primary, they must also add/remove

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   configuration for the zone from all secondaries.  This can be both
   inconvenient and error-prone; in addition, the steps required are
   dependent on the nameserver implementation.

   This document describes a method in which the list of zones is
   represented as a regular DNS zone (called a "catalog zone" here), and
   transferred using DNS zone transfers.  When entries are added to or
   removed from the catalog zone, it is distributed to the secondary
   nameservers just like any other zone.  Secondary nameservers can then
   add/remove/modify the zones they serve in accordance with the changes
   to the catalog zone.  Other use-cases of nameserver remote
   configuration by catalog zones are possible, where the catalog
   consumer might not be a secondary.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

   Catalog zone:  A DNS zone containing a DNS catalog, that is, a list
      of DNS zones and associated properties.

   Member zone:  A DNS zone whose configuration is published inside a
      catalog zone.

   Member node:  A DNS name in the Catalog zone representing a Member

   $CATZ:  Used in examples as a placeholder to represent the domain
      name of the catalog zone itself. $OLDCATZ and $NEWCATZ are used to
      discuss migration of a member zone from one catalog zone $OLDCATZ
      to another catalog zone $NEWCATZ.

   Catalog producer:  An entity that generates and is responsible for
      the contents of the catalog zone.

   Catalog consumer:  An entity that extracts information from the
      catalog zone (such as a DNS server that configures itself
      according to the catalog zone's contents).

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   This document makes use of terminology that is specific to the DNS,
   such as for transfer mechanisms (AXFR, IXFR), for record types (SOA,
   NS, PTR), and other technical terms (such as RDATA).  Since these
   terms have specific meanings in the DNS they are not expanded at
   first use in this document.  For definitions of those and other
   terms, see [RFC8499].

3.  Description

   A catalog zone is a DNS zone whose contents are specially crafted.
   Its resource records (RR) primarily constitute a list of PTR records
   referencing other DNS zones (so-called "member zones").  The catalog
   zone may contain other records indicating additional metadata (so-
   called "properties") associated with these member zones.

   Catalog consumers MUST ignore any RRs in the catalog zone for which
   no processing is specified or which are otherwise not supported by
   the implementation.

   Authoritative servers may be pre-configured with multiple catalog
   zones, each associated with a different set of configurations.

   Although the contents of a catalog zone are interpreted and acted
   upon by nameservers, a catalog zone is a regular DNS zone and so must
   adhere to the standards for DNS zones.

   A catalog zone is primarily intended for the management of a farm of
   authoritative nameservers, and should not be expected to be
   accessible from any recursive nameserver.

4.  Catalog Zone Structure

   A catalog zone MUST follow the usual rules for DNS zones.  In
   particular, SOA and NS record sets MUST be present and adhere to
   standard requirements (such as [RFC1982]).

   Although catalog zones are not intended to be queried via recursive
   resolution (see Section 7), at least one NS RR is still required so
   that a catalog zone is a syntactically correct DNS zone.  A single NS
   RR with a NSDNAME field containing the absolute name "invalid." is
   RECOMMENDED [RFC2606][RFC6761].

4.1.  Member Zones

   The list of member zones is specified as a collection of member
   nodes, represented by domain names under the owner name "zones" where
   "zones" is a direct child domain of the catalog zone.

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   The names of member zones are represented on the RDATA side (instead
   of as a part of owner names) of a PTR record, so that all valid
   domain names may be represented regardless of their length [RFC1035].
   This PTR record MUST be the only record in the PTR RRset with the
   same name.  The presence of more than one record in the RRset
   indicates a broken catalog zone which MUST NOT be processed (see
   Section 5.1).

   For example, if a catalog zone lists three zones "",
   "" and "", the member node RRs would appear
   as follows:

   <unique-1>.zones.$CATZ 0 IN PTR
   <unique-2>.zones.$CATZ 0 IN PTR
   <unique-3>.zones.$CATZ 0 IN PTR

   where <unique-N> is a label that tags each record in the collection.
   <unique-N> has a unique value in the collection.  When different
   <unique-N> labels hold the same PTR value (i.e., point to the same
   member zone), the catalog zone is broken and MUST NOT be processed
   (see Section 5.1).

   Member node labels carry no informational meaning beyond labeling
   member zones.  A changed label may indicate that the state for a zone
   needs to be reset (see Section 5.6).

   Having the zones uniquely tagged with the <unique-N> label ensures
   that additional RRs can be added below the member node (see
   Section 4.2).

   The CLASS field of every RR in a catalog zone MUST be IN (1).  The
   TTL field's value has no meaning in this context and SHOULD be

4.2.  Properties

   Catalog zone information is stored in the form of "properties".

   Properties are identified by their name, which is used as an owner
   name prefix for one or more record sets underneath a member node (or
   underneath the catalog zone apex), with RR type(s) as appropriate for
   the respective property.

   Known properties with the correct RR type, but which are for some
   reason invalid (for example because of an impossible value or because
   of an illegal number of RRs in the RRset), denote a broken catalog
   zone which MUST NOT be processed (see Section 5.1).

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   This document includes a set of initial properties which can be
   extended via the IANA registry defined and created in Section 8.
   Some properties are defined at the global level; others are scoped to
   apply only to a specific member zone.  This document defines a
   mandatory global property in Section 4.2.1.  The "zones" label from
   Section 4.1 can also be seen as a global property and is listed as
   such in the IANA registry in Section 8.  Member-specific properties
   are described in Section 4.3.

   Implementers may store additional information in the catalog zone
   with Custom properties, see Section 4.4.  The meaning of such custom
   properties is determined by the implementation in question.

4.2.1.  Schema Version (version property)

   The catalog zone schema version is specified by an integer value
   embedded in a TXT RR named version.$CATZ.  All catalog zones MUST
   have a TXT RRset named version.$CATZ with exactly one RR.

   Catalog consumers MUST NOT apply catalog zone processing to

   *  zones without the version property

   *  zones with a version property with more than one RR in the RRset

   *  zones with a version property without an expected value in the
      version.$CATZ TXT RR

   *  zones with a version property with a schema version value which is
      not implemented by the consumer (e.g. version "1")

   These conditions signify a broken catalog zone which MUST NOT be
   processed (see Section 5.1).

   For this memo, the value of the version.$CATZ TXT RR MUST be set to
   "2", i.e.:

   version.$CATZ 0 IN TXT "2"

   NB: Version 1 was used in a draft version of this memo and reflected
   the implementation first found in BIND 9.11.

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4.3.  Member Zone Properties

   Each member zone MAY have one or more additional properties,
   described in this chapter.  The member properties described in this
   document are all optional and implementations MAY choose to implement
   all, some or none of them.  Member zone properties are represented by
   RRsets below the corresponding member node.

4.3.1.  Change of Ownership (coo property)

   The coo property facilitates controlled migration of a member zone
   from one catalog to another.

   A Change Of Ownership is signaled by the coo property in the catalog
   zone currently "owning" the zone.  The name of the new catalog is the
   value of a PTR record in the relevant coo property in the old
   catalog.  For example if member "" will migrate from
   catalog zone $OLDCATZ to catalog zone $NEWCATZ, this appears in the
   $OLDCATZ catalog zone as follows:

   <unique-N>.zones.$OLDCATZ 0 IN PTR
   coo.<unique-N>.zones.$OLDCATZ 0 IN PTR $NEWCATZ

   The PTR RRset MUST consist of a single PTR record.  The presence of
   more than one record in the RRset indicates a broken catalog zone
   which MUST NOT be processed (see Section 5.1).

   When a consumer of a catalog zone $OLDCATZ receives an update which
   adds or changes a coo property for a member zone in $OLDCATZ, it does
   _not_ migrate the member zone immediately.  The migration has to wait
   for an update of $NEWCATZ. in which the member zone is present.  The
   consumer MUST verify, before the actual migration, that coo property
   pointing to $NEWCATZ is still present in $OLDCATZ.

   Unless the member node label (i.e., <unique-N>) for the member is the
   same in $NEWCATZ, all its associated state for a just migrated zone
   MUST be reset (see Section 5.6).  Note that the owner of $OLDCATZ
   allows for the zone associated state to be taken over by the owner of
   $NEWCATZ by default.  To prevent the takeover of state, the owner of
   $OLDCATZ must remove this state by updating the associated properties
   or by performing a zone state reset (see Section 5.6) before or
   simultaneous with adding the coo property. (see also Section 7)

   The old owner may remove the member zone containing the coo property
   from $OLDCATZ once it has been established that all its consumers
   have processed the Change of Ownership.

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4.3.2.  Groups (group property)

   With a group property, consumer(s) can be signaled to treat some
   member zones within the catalog zone differently.

   The consumer MAY apply different configuration options when
   processing member zones, based on the value of the group property.  A
   group property value is stored as the entire RDATA of a TXT record
   directly below the member node.  The exact handling of the group
   property value is left to the consumer's implementation and

   The producer MAY assign a group property to all, some, or none of the
   member zones within a catalog zone.  The producer MAY assign more
   than one group property to one member zone.  This will make it
   possible to transfer group information for different consumer
   operators in a single catalog zone.  Implementations MAY facilitate
   mapping of a specific group value to specific configuration
   configurable _on a per catalog zone basis_ to allow for producers
   that publish their catalog zone at multiple consumer operators.
   Consumer operators SHOULD namespace their group values to reduce the
   risk of having to resolve clashes.

   The consumer MUST ignore group values it does not understand.  When a
   consumer encounters multiple group values for a single member zone,
   it MAY choose to process all, some or none of them.  This is left to
   the implementation.  Example

   Group properties are represented by TXT resource records.  The record
   content has no pre-defined meaning.  Their interpretation is purely a
   matter of agreement between the producer and the consumer(s) of the

   For example, the "foo" group could be agreed to indicate that a zone
   not be signed with DNSSEC.  Conversely, an agreement could define
   that group names starting with "operator-" indicate in which way a
   given DNS operator should set up certain aspects of the member zone's
   DNSSEC configuration.

   Assuming that the catalog producer and consumer(s) have established
   such agreements, consider the following catalog zone (snippet) which
   signals to consumer(s) how to treat DNSSEC for the zones
   "" and "":

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   <unique-1>.zones.$CATZ        0 IN PTR
   group.<unique-1>.zones.$CATZ  0 IN TXT    "foo"
   <unique-2>.zones.$CATZ        0 IN PTR
   group.<unique-2>.zones.$CATZ  0 IN TXT    "operator-x-foo"
   group.<unique-2>.zones.$CATZ  0 IN TXT    "operator-y" "bar"

   In this scenario, consumer(s) shall, by agreement, not sign the
   member zone "" with DNSSEC.  For "", the
   consumers, at two different operators, will configure the member zone
   to be signed with a specific combination of settings.  The group
   value that indicates that depends on what has been agreed with each
   operator ("operator-x-foo" vs. "operator-y" "bar").

4.4.  Custom Properties (*.ext properties)

   Implementations and operators of catalog zones may choose to provide
   their own properties.  Custom properties can occur both globally, or
   for a specific member zone.  To prevent a name clash with future
   properties, such properties MUST be represented below the label

   "ext" is not a placeholder.  A custom property is named as follows:

   ; a global custom property:

   ; a member zone custom property:

   <property-prefix> may consist of one or more labels.

   Implementations SHOULD namespace their custom properties to limit
   risk of clashes with other implementations of catalog zones.  This
   can be achieved by using two labels as the <property-prefix>, so that
   the name of the implementation is included in the prefix: <some-

   Implementations MAY use such properties on the member zone level to
   store additional information about member zones, for example to flag
   them for specific treatment.

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   Further, implementations MAY use custom properties on the global
   level to store additional information about the catalog zone itself.
   While there may be many use cases for this, a plausible one is to
   store default values for custom properties on the global level, then
   overriding them using a property of the same name on the member level
   (= under the ext label of the member node) if so desired.  A property
   agreement between producer and consumer should clearly define what
   semantics apply, and whether a property is global, member, or both.

   The meaning of the custom properties described in this section is
   determined by the implementation alone, without expectation of

5.  Nameserver Behavior

5.1.  General Requirements

   As it is a regular DNS zone, a catalog zone can be transferred using
   DNS zone transfers among nameservers.

   Catalog updates should be automatic, i.e., when a nameserver that
   supports catalog zones completes a zone transfer for a catalog zone,
   it SHOULD apply changes to the catalog within the running nameserver
   automatically without any manual intervention.

   Nameservers MAY allow loading and transfer of broken zones with
   incorrect catalog zone syntax (as they are treated as regular zones).
   The reason a catalog zone is considered broken SHOULD be communicated
   clearly to the operator (e.g. through a log message).

   When a previously correct catalog zone becomes a broken catalog zone,
   because of an update through an incremental transfer or otherwise, it
   loses its catalog meaning.  No special processing occurs.  Member
   zones previously configured by this catalog MUST NOT be removed or
   reconfigured in any way.

   If a name server restarts with a broken catalog zone, the broken
   catalog SHOULD NOT prevent the name server from starting up and
   serving the member zones in the last valid version of the catalog

   Processing of a broken catalog SHALL start (or resume) when the
   catalog turns into a correct catalog zone, for example by an
   additional update (through zone transfer or updates) fixing the
   catalog zone.

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   Similarly, when a catalog zone expires, it loses its catalog meaning
   and MUST no longer be processed as such.  No special processing
   occurs until the zone becomes fresh again.

5.2.  Member zone name clash

   If there is a clash between an existing zone's name (either from an
   existing member zone or otherwise configured zone) and an incoming
   member zone's name (via transfer or update), the new instance of the
   zone MUST be ignored and an error SHOULD be logged.

   A clash between an existing member zone's name and an incoming member
   zone's name (via transfer or update), may be an attempt to migrate a
   zone to a different catalog, but should not be treated as one except
   as described in Section 4.3.1.

5.3.  Member zone removal

   When a member zone is removed from a specific catalog zone, a
   consumer MUST NOT remove the zone and associated state data if the
   zone was not configured from that specific catalog zone.  Only when
   the zone was configured from a specific catalog zone, and the zone is
   removed as a member from that specific catalog zone, the zone and
   associated state (such as zone data and DNSSEC keys) MUST be removed
   from the consumer.  Consumer operators may consider to temporarily
   archive associated state to facilitate mistake recovery.

5.4.  Member node name change

   When via a single update or transfer, the member node's label value
   (<unique-N>) changes, catalog consumers MUST process this as a member
   zone removal including all the zone's associated state (as described
   in Section 5.3), immediately followed by processing the member as a
   newly to be configured zone in the same catalog.

5.5.  Migrating member zones between catalogs

   If all consumers of the catalog zones involved support the coo
   property, it is RECOMMENDED to perform migration of a member zone by
   following the procedure described in Section 4.3.1.  Otherwise, a
   migration of a member zone from a catalog zone $OLDCATZ to a catalog
   zone $NEWCATZ has to be done by: first removing the member zone from
   $OLDCATZ; second adding the member zone to $NEWCATZ.

   If in the process of a migration some consumers of the involved
   catalog zones did not catch the removal of the member zone from
   $OLDCATZ yet (because of a lost packet or downtime or otherwise), but
   did already see the update of $NEWCATZ, they may consider the update

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   adding the member zone in $NEWCATZ to be a name clash (see
   Section 5.2) and as a consequence the member is not migrated to
   $NEWCATZ.  This possibility needs to be anticipated with a member
   zone migration.  Recovery from such a situation is out of the scope
   of this document.  It may for example entail a manually forced
   retransfer of $NEWCATZ to consumers after they have been detected to
   have received and processed the removal of the member zone from

5.6.  Zone-associated state reset

   It may be desirable to reset state (such as zone data and DNSSEC
   keys) associated with a member zone.

   A zone state reset may be performed by a change of the member node's
   name (see Section 5.4).

6.  Implementation and Operational Notes

   Although any valid domain name can be used for the catalog name
   $CATZ, a catalog producer MUST NOT use names that are not under the
   control of the catalog producer (with the exception of reserved
   names).  It is RECOMMENDED to use either a domain name owned by the
   catalog producer, or to use a name under a suitable name such as
   "invalid."  [RFC6761].

   Catalog zones on secondary nameservers would have to be set up
   manually, perhaps as static configuration, similar to how ordinary
   DNS zones are configured when catalog zones or another automatic
   configuration mechanism are not in place.  The secondary additionally
   needs to be configured as a catalog consumer for the catalog zone to
   enable processing of the member zones in the catalog, such as
   automatic synchronization of the member zones for secondary service.

   Operators of catalog consumers should note that secondary name
   servers may receive DNS NOTIFY messages [RFC1996] for zones before
   they are seen as newly added member zones to the catalog from which
   that secondary is provisioned.

   Although they are regular DNS zones, catalog zones contain only
   information for the management of a set of authoritative nameservers.
   To prevent unintended exposure to other parties, operators SHOULD
   limit the systems able to query these zones.

   Querying/serving catalog zone contents may be inconvenient via DNS
   due to the nature of their representation.  An administrator may
   therefore want to use a different method for looking at data inside
   the catalog zone.  Typical queries might include dumping the list of

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   member zones, dumping a member zone's effective configuration,
   querying a specific property value of a member zone, etc.  Because of
   the structure of catalog zones, it may not be possible to perform
   these queries intuitively, or in some cases, at all, using DNS QUERY.
   For example, it is not possible to enumerate the contents of a
   multivalued property (such as the list of member zones) with a single
   QUERY.  Implementations are therefore advised to provide a tool that
   uses either the output of AXFR or an out-of-band method to perform
   queries on catalog zones.

   Great power comes with great responsibility: Catalog zones simplify
   zone provisioning by orchestrating zones on secondary name servers
   from a single data source - the catalog.  Hence, the catalog producer
   has great power and changes must be treated carefully.  For example
   if the catalog is generated by some script and this script for
   whatever reason generates an empty catalog, millions of member zones
   may get deleted from their secondaries within seconds and all the
   affected domains may be offline in a blink of an eye.

7.  Security Considerations

   As catalog zones are transmitted using DNS zone transfers, it is
   RECOMMENDED that catalog zone transfers are protected from unexpected
   modifications by way of authentication, for example by using TSIG
   [RFC8945], or Strict or Mutual TLS authentication with DNS Zone
   transfer over TLS or QUIC [RFC9103].

   Use of DNS UPDATE [RFC2136] to modify the content of catalog zones
   SHOULD similarly be authenticated.

   Zone transfers of member zones SHOULD similarly be authenticated.
   TSIG shared secrets used for member zones SHOULD NOT be mentioned in
   the catalog zone data.  However, key identifiers may be shared within
   catalog zones.

   Catalog zones reveal the zones served by their consumers, including
   their properties.  To prevent unintentional exposure of catalog zone
   contents, it is RECOMMENDED to limit the systems able to query them
   and to conduct catalog zone transfers confidentially [RFC9103].

   As with regular zones, primary and secondary nameservers for a
   catalog zone may be operated by different administrators.  The
   secondary nameservers may be configured as a catalog consumer to
   synchronize catalog zones from the primary, but the primary's
   administrators may not have any administrative access to the

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   Administrative control over what zones are served from the configured
   name servers shifts completely from the server operator (consumer) to
   the "owner" (producer) of the catalog zone content.  To prevent
   unintended provisioning of zones, consumer(s) SHOULD scope the set of
   admissible member zones by any means deemed suitable (such as
   statically, via regular expressions, or dynamically, by verifying
   against another database before accepting a member zone).

   With migration of member zones between catalogs using the coo
   property, it is possible for the owner of the target catalog (i.e.,
   $NEWCATZ) to take over all its associated state with the zone from
   the original owner (i.e., $OLDCATZ) by maintaining the same member
   node label (i.e., <unique-N>).  To prevent the takeover of the zone
   associated state, the original owner has to enforce a zone state
   reset by changing the member node label (see Section 5.6) before or
   simultaneously with adding the coo property.

8.  IANA Considerations

   IANA is requested to create a registry on the "Domain Name System
   (DNS) Parameters" IANA web page as follows:

   Registry Name:  DNS Catalog Zones Properties

   Assignment Policy:  Expert Review, except for property prefixes
      ending in the label "ext", which are for Private Use.

   Reference:  [this document]

   Note:  This registry does not apply to Catalog Zones version "1", but
      applies to Catalog Zones version "2" as specified in [this

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    | Property prefix | Description          | Status    | Reference |
    | zones           | List of member zones | Standards | [this     |
    |                 |                      | Track     | document] |
    | version         | Schema version       | Standards | [this     |
    |                 |                      | Track     | document] |
    | coo             | Change of Ownership  | Standards | [this     |
    |                 |                      | Track     | document] |
    | group           | Group                | Standards | [this     |
    |                 |                      | Track     | document] |
    | *.ext           | Custom properties    | Private   | [this     |
    |                 |                      | Use       | document] |

                                 Table 1

   The meanings of the fields are as follows:

   Property prefix:  One or more domain name labels

   Description:  A human readable short description or name for the

   Status:  IETF Document status or "External" if not documented in an
      IETF document.

   Reference:  A stable reference to the document in which this property
      is defined.

9.  Acknowledgements

   Our deepest thanks and appreciation go to Stephen Morris, Ray Bellis
   and Witold Krecicki who initiated this draft and did the bulk of the

   Catalog zones originated as the chosen method among various proposals
   that were evaluated at ISC for easy zone management.  The chosen
   method of storing the catalog as a regular DNS zone was proposed by
   Stephen Morris.

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   The initial authors discovered that Paul Vixie's earlier [Metazones]
   proposal implemented a similar approach and reviewed it.  Catalog
   zones borrow some syntax ideas from Metazones, as both share this
   scheme of representing the catalog as a regular DNS zone.

   Thanks to Leo Vandewoestijne.  Leo's presentation in the DNS devroom
   at the FOSDEM'20 [FOSDEM20] was one of the motivations to take up and
   continue the effort of standardizing catalog zones.

   Thanks to Joe Abley, David Blacka, Brian Conry, Klaus Darilion, Brian
   Dickson, Tony Finch, Evan Hunt, Shane Kerr, Warren Kumari, Patrik
   Lundin, Matthijs Mekking, Victoria Risk, Josh Soref, Petr Spacek,
   Michael StJohns, Carsten Strotmann and Tim Wicinski for reviewing
   draft proposals and offering comments and suggestions.

10.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              DOI 10.17487/RFC1982, August 1996,

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,

   [RFC2606]  Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS
              Names", BCP 32, RFC 2606, DOI 10.17487/RFC2606, June 1999,

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <>.

   [RFC8945]  Dupont, F., Morris, S., Vixie, P., Eastlake 3rd, D.,
              Gudmundsson, O., and B. Wellington, "Secret Key
              Transaction Authentication for DNS (TSIG)", STD 93,
              RFC 8945, DOI 10.17487/RFC8945, November 2020,

   [RFC9103]  Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A.
              Mankin, "DNS Zone Transfer over TLS", RFC 9103,
              DOI 10.17487/RFC9103, August 2021,

11.  Informative References

   [FOSDEM20] Vandewoestijne, L., "Extending Catalog zones - another
              approach in automating maintenance", 2020,

              Vixie, P., "Federated Domain Name Service Using DNS
              Metazones", 2005,

Appendix A.  Catalog Zone Example

   The following is a full example of a catalog zone containing three
   member zones with various properties:

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   catalog.invalid.                                0  SOA   invalid. (
                           invalid. 1625079950 3600 600 2147483646 0 )
   catalog.invalid.                                0  NS    invalid.
   example.vendor.ext.catalog.invalid.             0  CNAME
   version.catalog.invalid.                        0  TXT   "2"
   nj2xg5b.zones.catalog.invalid.                  0  PTR
   nvxxezj.zones.catalog.invalid.                  0  PTR
   group.nvxxezj.zones.catalog.invalid.            0  TXT   (
                           "operator-x-foo" )
   nfwxa33.zones.catalog.invalid.                  0  PTR
   coo.nfwxa33.zones.catalog.invalid.              0  PTR   (
                           newcatz.invalid. )
   group.nfwxa33.zones.catalog.invalid.            0  TXT   (
                           "operator-y-bar" )
   metrics.vendor.ext.nfwxa33.zones.catalog.invalid. 0  CNAME (

Appendix B.  Implementation Status

   *Note to the RFC Editor*: please remove this entire appendix before

   In the following implementation status descriptions, "DNS Catalog
   Zones" refers to DNS Catalog Zones version 2 as described in this
   document.  Version 1 of catalog zones was initially developed by ISC
   for BIND, but never standardized in the IETF.  Support for version 1
   catalog zones is explicitly mentioned per implementation.  Support
   for the coo and group properties are also explicitly mentioned per

   *  Knot DNS 3.1 (released August 2, 2021) supports both producing and
      consuming of catalog zones, including the group property.

   *  PowerDNS from version 4.7 (released October 3, 2022) supports both
      producing and consuming of catalog zones version 2 and consuming
      of catalog zones version 1.  PowerDNS does support the coo
      property, and the group property on the producing side.

   *  Proof of concept python scripts (
      Hackathon/NSDCatZ) that can be used for both generating and
      consuming DNS Catalog Zones with NSD have been developed during
      the hackathon at the IETF-109.

   *  BIND 9.18.3+ supports version 2 catalog zones as described in this
      document including the coo property, as well as version 1 catalog

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   Interoperability between the above implementations has been tested
   during the hackathon at the IETF-109.

Appendix C.  Change History

   *Note to the RFC Editor*: please remove this entire appendix before

   *  draft-muks-dnsop-dns-catalog-zones-00

   |  Initial public draft.

   *  draft-muks-dnsop-dns-catalog-zones-01

   |  Added Witold, Ray as authors.  Fixed typos, consistency issues.
   |  Fixed references.  Updated Area.  Removed newly introduced custom
   |  RR TYPEs.  Changed schema version to 1.  Changed TSIG requirement
   |  from MUST to SHOULD.  Removed restrictive language about use of
   |  DNS QUERY.  When zones are introduced into a catalog zone, a
   |  primary SHOULD first make the new zones available for transfers
   |  first (instead of MUST).  Updated examples, esp. use IPv6 in
   |  examples per Fred Baker.  Add catalog zone example.

   *  draft-muks-dnsop-dns-catalog-zones-02

   |  Addressed some review comments by Patrik Lundin.

   *  draft-muks-dnsop-dns-catalog-zones-03

   |  Revision bump.

   *  draft-muks-dnsop-dns-catalog-zones-04

   |  Reordering of sections into more logical order.  Separation of
   |  multi-valued properties into their own category.

   *  draft-toorop-dnsop-dns-catalog-zones-00

   |  New authors to pickup the editor pen on this draft
   |  Remove data type definitions for zone properties Removing
   |  configuration of member zones through zone properties altogether
   |  Remove Open issues and discussion Appendix, which was about zone
   |  options (including primary/secondary relationships) only.

   *  draft-toorop-dnsop-dns-catalog-zones-01

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   |  Added a new section "The Serial Property", introducing a new
   |  mechanism which can help with disseminating zones from the primary
   |  to the secondary nameservers in a timely fashion more reliably.
   |  Three different ways to provide a "serial" property with a member
   |  zone are offered to or the workgroup for discussion.
   |  Added a new section "Implementation Status", listing production
   |  ready, upcoming and Proof of Concept implementations, and
   |  reporting on interoperability of the different implementations.

   *  draft-toorop-dnsop-dns-catalog-zones-02

   |  Adding the coo property for zone migration in a controlled fashion
   |  Adding the group property for reconfigure settings of member zones
   |  in an atomic update
   |  Adding the epoch property to reset zone associated state in a
   |  controlled fashion

   *  draft-toorop-dnsop-dns-catalog-zones-03

   |  Big cleanup!
   |  Introducing the terms catalog consumer and catalog producer
   |  Reorganized topics to create a more coherent whole
   |  Properties all have consistent format now
   |  Try to assume the least possible from implementations w.r.t.:
   |  1) Predictability of the <unique-N> IDs of member zones
   |  2) Whether or not fallback catalog zones can be found for a member
   |  3) Whether or not a catalog consumer can maintain state

   *  draft-toorop-dnsop-dns-catalog-zones-04

   |  Move Implementation status to appendix
   |  Miscellaneous textual improvements
   |  coo property points to $NEWCATZ (and not zones.$NEWCATZ)

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   |  Remove suggestion to increase serial and remove member zone from
   |  $OLDCATZ after migration
   |  More consistent usage of the terms catalog consumer and catalog
   |  producer throughout the document
   |  Better (safer) description of resetting refresh timers of member
   |  zones with the serial property
   |  Removing a member MUST remove zone associated state
   |  Make authentication requirements a bit less prescriptive in
   |  security considerations
   |  Updated implementation status for KnotDNS
   |  Describe member node name changes and update "Zone associated
   |  state reset" to use that as the mechanism for it.
   |  Add Peter Thomassen as co-author
   |  Complete removal of the epoch property.  We consider consumer
   |  optimizations with predictable member node labels (for example
   |  based on a hash) out of the scope of this document.
   |  Miscellaneous editorial improvements

   *  draft-toorop-dnsop-dns-catalog-zones-05

   |  Add Kees Monshouwer as co-author
   |  Removed the "serial" property
   |  Allow custom properties on the global level

   *  draft-toorop-dnsop-dns-catalog-zones-06

   |  Move administrative control explanation to Security Considerations
   |  Move comment on query methods to Implementation Notes
   |  Clarify what happens on expiry
   |  Clarify catalog consumer behavior when MUST condition is violated
   |  Better text on ordering of operations for Change of Ownership
   |  Suggest to namespace custom properties

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   |  Clarify how to handle property record with wrong type
   |  Cover the case of multiple different <unique-N>'s having the same
   |  value
   |  Recommendations for naming catalog zones
   |  Add and operational note about notifies for not yet existing zones
   |  Add text about name server restarts with broken zones
   |  Great power comes with great responsibility (Thanks Klaus!)
   |  Mention the new BIND implementation
   |  All invalid properties cause a broken catalog zone, including
   |  invalid group and version properties.
   |  Add Aram Sargsyan as author (he did the BIND9 implementation)
   |  group properties can have more than one value

   *  draft-toorop-dnsop-dns-catalog-zones-07

   |  Some spelling fixes from Tim Wicinski and Josh Soref
   |  Replace SHOULDs with MUSTs for ignoring things that are
   |  meaningless to a catalog consumer (Thanks Michael StJohns)
   |  Update the list of people to thank in the Acknowledgements section
   |  Mention PowerDNS support of catalog zones from version 4.7.0
   |  onwards

   *  draft-toorop-dnsop-dns-catalog-zones-08

   |  Address AD Review comments (editorial only)
   |  When DoT is mentioned, also mention now-standardized DoQ

   *  draft-toorop-dnsop-dns-catalog-zones-08

   |  Editorial nits from David Blacka, Lars Eggert, Russ Housley, Erik
   |  Kline, É (U+00C9)ric Vyncke and Paul Wouters
   |  Addes a Catalog Zone Exampla

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   |  Mention that the document uses DNS specific terminology and
   |  reference RFC8499
   |  Added IANA Considerations sections, with a registry for Catalog
   |  Zones properties
   |  Updated Implementation status also with respect to Catalog zones
   |  version "1" support
   |  Updates to Rename "group properties" to "group property values" or
   |  "group values" to reduce confusion about who will determine those
   |  values (operators and not implementations)
   |  Change example group values in non descriptive names
   |  Add some more clarifications on that and how group values are
   |  determined in producer/consumer agreements
   |  Stronger checking suggestion (SHOULD instead of MAY) in accepting
   |  member zones by consumers in the Security section
   |  Added mistake recovery text to the Member zone removal section
   |  Replace vague language ("meaningless") with more precise wording
   |  Catalog consumers that know only version "2" MUST not process
   |  version "1" catalog zones and consider it broken.
   |  The entire RDATA of a group property is it's value

Authors' Addresses

   Peter van Dijk
   Den Haag

   Libor Peltan

   Ondrej Sury
   Internet Systems Consortium

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   Willem Toorop
   NLnet Labs
   Science Park 400
   1098 XH Amsterdam

   Kees Monshouwer

   Peter Thomassen
   deSEC, SSE - Secure Systems Engineering

   Aram Sargsyan
   Internet Systems Consortium

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