Skip to main content

DNS Catalog Zones

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Peter van Dijk , Libor Peltan , Ondřej Surý , Willem Toorop , Leo Vandewoestijne , Peter Thomassen
Last updated 2021-10-25 (Latest revision 2021-08-25)
Replaces draft-toorop-dnsop-dns-catalog-zones
RFC stream Internet Engineering Task Force (IETF)
OPSDIR Last Call Review Incomplete, due 2022-12-13
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd (None)
IESG IESG state I-D Exists
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD (None)
Send notices to (None)
DNSOP Working Group                                          P. van Dijk
Internet-Draft                                                  PowerDNS
Intended status: Standards Track                               L. Peltan
Expires: 28 April 2022                                            CZ.NIC
                                                                 O. Sury
                                             Internet Systems Consortium
                                                               W. Toorop
                                                              NLnet Labs
                                                       L. Vandewoestijne
                                                            P. Thomassen
                                       deSEC, Secure Systems Engineering
                                                         25 October 2021

                           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 28 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

van Dijk, et al.          Expires 28 April 2022                 [Page 1]
Internet-Draft              dns-catalog-zones               October 2021

   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 Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Catalog Zone Structure  . . . . . . . . . . . . . . . . . . .   4
     4.1.  SOA and NS Records  . . . . . . . . . . . . . . . . . . .   4
     4.2.  Catalog Zone Schema Version . . . . . . . . . . . . . . .   5
     4.3.  List of Member Zones  . . . . . . . . . . . . . . . . . .   5
   5.  Properties  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  The Change of Ownership (coo) Property  . . . . . . . . .   6
     5.2.  The Group Property  . . . . . . . . . . . . . . . . . . .   7
       5.2.1.  Group Property Example  . . . . . . . . . . . . . . .   7
     5.3.  The Serial Property . . . . . . . . . . . . . . . . . . .   8
       5.3.1.  The SERIAL Resource Record  . . . . . . . . . . . . .   9
       5.3.2.  SERIAL RDATA Wire Format  . . . . . . . . . . . . . .   9
       5.3.3.  SERIAL Presentation Format  . . . . . . . . . . . . .   9
       5.3.4.  SERIAL RR Usage . . . . . . . . . . . . . . . . . . .   9
     5.4.  Custom properties . . . . . . . . . . . . . . . . . . . .  10
   6.  Nameserver Behavior . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  General Requirements  . . . . . . . . . . . . . . . . . .  10
     6.2.  Member zone name clash  . . . . . . . . . . . . . . . . .  11
     6.3.  Member zone removal . . . . . . . . . . . . . . . . . . .  11
     6.4.  Member node name change . . . . . . . . . . . . . . . . .  11
     6.5.  Migrating member zones between catalogs . . . . . . . . .  11
     6.6.  Zone associated state reset . . . . . . . . . . . . . . .  12
   7.  Implementation Notes  . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  SERIAL RR type  . . . . . . . . . . . . . . . . . . . . .  13
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   11. Normative References  . . . . . . . . . . . . . . . . . . . .  14
   12. Informative References  . . . . . . . . . . . . . . . . . . .  15
   Appendix A.  Implementation Status  . . . . . . . . . . . . . . .  15
   Appendix B.  Change History (to be removed before final
           publication)  . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

van Dijk, et al.          Expires 28 April 2022                 [Page 2]
Internet-Draft              dns-catalog-zones               October 2021

1.  Introduction

   The content of a DNS zone is synchronized amongst 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 the
   zone from all secondaries, either manually or via an external
   application.  This can be both inconvenient and error-prone; it is
   also dependent on the nameserver implementation.

   This document describes a method in which the catalog is represented
   as a regular DNS zone (called a "catalog zone" here), and transferred
   using DNS zone transfers.  As zones are added to or removed from the
   catalog zone, these changes are distributed to the secondary
   nameservers in the normal way.  The secondary nameservers 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  The 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 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

van Dijk, et al.          Expires 28 April 2022                 [Page 3]
Internet-Draft              dns-catalog-zones               October 2021

      catalog zone (such as a DNS server that configures itself
      according to the catalog zone's contents).

3.  Description

   A catalog zone is a DNS zone whose contents are specially crafted.
   Its records 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 SHOULD ignore any RR in the catalog zone which is
   meaningless or useless to the implementation.

   Authoritative servers may be preconfigured 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 such zones.

   A catalog zone is primarily intended for the management of a farm of
   authoritative nameservers.  The content of catalog zones may not be
   accessible from any recursive nameserver.

4.  Catalog Zone Structure

4.1.  SOA and NS Records

   As with any other DNS zone, a catalog zone MUST have a syntactically
   correct SOA record and at least one NS record at its apex.

   The SOA record's SERIAL, REFRESH, RETRY and EXPIRE fields [RFC1035]
   are used during zone transfer.  A catalog zone's SOA SERIAL field
   MUST increase when an update is made to the catalog zone's contents
   as per serial number arithmetic defined in [RFC1982].  Otherwise,
   catalog consumers might not notice updates to the catalog zone's

   There is no requirement to be able to query the catalog zone via
   recursive nameservers.  Catalog consumers MUST ignore and MUST NOT
   assume or require NS records at the apex.  However, at least one is
   still required so that catalog zones are syntactically correct DNS
   zones.  A single NS RR with a NSDNAME field containing the absolute
   name "invalid." is RECOMMENDED [RFC2606].

van Dijk, et al.          Expires 28 April 2022                 [Page 4]
Internet-Draft              dns-catalog-zones               October 2021

4.2.  Catalog Zone Schema Version

   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 at least one RR.  Catalog
   consumers MUST NOT apply catalog zone processing to zones without the
   expected value in one of the RRs in the version.$CATZ TXT RRset, but
   they may be transferred as ordinary zones.  For this memo, the value
   of one of the RRs in the version.CATZ TXT RRset MUST be set to "2",

   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.

4.3.  List of 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.

   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.  More than one record in the RRset denotes a broken
   catalog zone which MUST NOT be processed (see Section 6.1).

   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 an unique value in the collection.

   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 6.6).

   Having the zones uniquely tagged with the <unique-N> label ensures
   that additional RRs can be added below the member node (see
   Section 5).

van Dijk, et al.          Expires 28 April 2022                 [Page 5]
Internet-Draft              dns-catalog-zones               October 2021

   The CLASS field of every RR in a catalog zone MUST be IN (1).

   The TTL field's value is not defined by this memo.  Catalog zones are
   for authoritative nameserver management only and are not intended for
   general querying via recursive resolvers.

5.  Properties

   Each member zone MAY have one or more additional properties,
   described in this chapter.  These properties are completely optional
   and catalog consumers SHOULD ignore those it does not understand.
   Properties are represented by RRsets below the corresponding member

5.1.  The 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 in
   the value of a PTR record 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.  More than one
   record in the RRset denotes a broken catalog zone which MUST NOT be
   processed (see Section 6.1).

   When a consumer of catalog zone $OLDCATZ receives an update which
   adds or changes a coo property for a member zone in $OLDCATZ
   signalling a new owner $NEWCATZ, it does _not_ migrate the member
   zone immediately.

   This is because the catalog consumer may not have the <unique-N>
   identifier associated with the member zone in $NEWCATZ and because
   name servers do not index Resource Records by RDATA, it may not know
   wether or not the member zone is configured in $NEWCATZ at all.  It
   may have to wait for an update of $NEWCATZ adding or changing that
   member zone.  When a consumer of catalog zone $NEWCATZ receives an
   update of $NEWCATZ which adds or changes a member zone, _and_ that
   consumer had the member zone associated with $OLDCATZ, _and_ there is
   a coo property of the member zone in $OLDCATZ pointing to $NEWCATZ,
   _only then_ it will reconfigure the member zone with the for $NEWCATZ
   preconfigured settings.

van Dijk, et al.          Expires 28 April 2022                 [Page 6]
Internet-Draft              dns-catalog-zones               October 2021

   Unless the member node label (i.e. <unique-N>) for the member is the
   same in $NEWCATZ, all associated state for a just migrated zone MUST
   be reset (see Section 6.6).  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, the owner of $OLDCATZ
   has to enforce a zone state reset by changing the member node label
   (see Section 6.6) before or simultaneous with adding the coo
   property. (see also Section 8)

   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.

5.2.  The Group Property

   With a group property, consumer(s) can be signalled 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.
   The exact handling of configuration referred to by the group property
   value is left to the consumer's implementation and configuration.
   The property is defined by a TXT record in the sub-node labelled

   The producer MAY assign a group property to all, some, or none of the
   member zones within a catalog zone.  The producer MUST NOT assign
   more than one group property to one member zone.

   The consumer MUST ignore either all or none of the group properties
   in a catalog zone.

   The value of the TXT record MUST be at most 255 octets long and MUST
   NOT contain whitespace characters.  The consumer MUST interpret the
   value case-sensitively.

5.2.1.  Group Property Example

   <unique-1>.zones.$CATZ        0 IN PTR
   group.<unique-1>.zones.$CATZ  0 IN TXT    sign-with-nsec3
   <unique-2>.zones.$CATZ        0 IN PTR
   group.<unique-2>.zones.$CATZ  0 IN TXT    nodnssec

   In this case, the consumer might be implemented and configured in the
   way that the member zones with "nodnssec" group assigned will not be
   signed with DNSSEC, and the zones with "sign-with-nsec3" group
   assigned will be signed with DNSSEC with NSEC3 chain.

van Dijk, et al.          Expires 28 April 2022                 [Page 7]
Internet-Draft              dns-catalog-zones               October 2021

   By generating the catalog zone (snippet) above, the producer signals
   how the consumer shall treat DNSSEC for the zones and, respectively.

5.3.  The Serial Property

   The serial property helps in increasing reliability of zone update
   signaling and may help in reducing NOTIFY and SOA query traffic.

   The current default mechanism for prompting notifications of zone
   changes from a primary nameserver to the secondaries via DNS NOTIFY
   [RFC1996], can be unreliable due to packet loss, or secondary
   nameservers temporarily not being reachable.  In such cases the
   secondary might pick up the change only after the refresh timer runs
   out, which might take long and be out of the control of the primary
   nameserver operator.  Low refresh values in the zones being served
   can alleviate update delays, but burden both the primary and
   secondary nameservers with more refresh queries, especially with
   larger numbers of secondary nameservers serving large numbers of
   zones.  To mitigate this, updates of zones MAY be signalled via
   catalog zones with the help of a serial property.

   The serial number in the SOA record of the most recent version of a
   member zone MAY be provided by a serial property.  When a serial
   property is present for a member zone, catalog consumers MAY assume
   this number to be the current serial number in the SOA record of the
   most recent version of the member zone.

   Catalog consumers which are secondary for that member zone, MAY
   compare the serial property with the SOA serial since the last time
   the zone was fetched.  When the serial property is larger, the
   secondary MAY initiate a zone transfer immediately without doing a
   SOA query first.  The SOA query may be omitted, because the SOA
   serial has been obtained reliably via the catalog zone already.

   Secondary nameservers MAY be configured to postpone the next refresh
   by the SOA refresh value of the member zone (counted since the
   transfer of the catalog zone) when the value of the serial property
   was found to be equal to the served zone, the same way as if it had
   queried the primary SOA directly and found it equal.  Note that for
   this mechanism it is essential that the catalog producer is keeping
   the serial property up to date with the SOA serial value of the
   member zone at all times.  The catalog may not be lagging behind.
   Increased robustness in having the latest version of a zone may be a
   reason to *not* configure a secondary nameserver with this mechanism.

van Dijk, et al.          Expires 28 April 2022                 [Page 8]
Internet-Draft              dns-catalog-zones               October 2021

   Primary nameservers MAY be configured to omit sending DNS NOTIFY
   messages to secondary nameservers which are known to process the
   serial property of the member zones in the associated catalog.
   However they MAY also combine signalling of zone changes with the
   serial property of a member zone, as well as sending DNS NOTIFY
   messages, to anticipate slow updates of the catalog zone (due to
   packet loss or other reasons) and to cater for secondaries that are
   not a catalog consumer processing the serial property.

   All comparisons of serial numbers MUST use "Serial number
   arithmetic", as defined in [RFC1982]

5.3.1.  The SERIAL Resource Record

   The serial property value is provided with a SERIAL Resource Record.
   The Type value for the SERIAL RR is TBD.  The SERIAL RR is class
   independent.  The RDATA of the resource record consist of a single
   field: Serial.

5.3.2.  SERIAL RDATA Wire Format

   The SERIAL RDATA wire format is encoded as follows:

                        1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                            Serial                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  The Serial Field

   The Serial field is a 32-bit unsigned integer in network byte order.
   It is the serial number of the member zone's SOA record ([RFC1035]
   section 3.3.13).

5.3.3.  SERIAL Presentation Format

   The presentation format of the RDATA portion is as follows:

   The Serial fields is represented as an unsigned decimal integer.

5.3.4.  SERIAL RR Usage

   The serial property of a member zone is provided by a SERIAL RRset
   with a single SERIAL RR named serial.<unique-N>.zones.$CATZ.

van Dijk, et al.          Expires 28 April 2022                 [Page 9]
Internet-Draft              dns-catalog-zones               October 2021

   For example, if a catalog zone lists three zones "",
   "" and "", and a serial property is provided
   for each of them, the RRs would appear as follows:

   <unique-1>.zones.$CATZ        0 IN PTR
   serial.<unique-1>.zones.$CATZ 0 IN SERIAL 3
   <unique-2>.zones.$CATZ        0 IN PTR
   serial.<unique-2>.zones.$CATZ 0 IN SERIAL 1634730530
   <unique-3>.zones.$CATZ        0 IN PTR
   serial.<unique-3>.zones.$CATZ 0 IN SERIAL 2020112405

5.4.  Custom properties

   More properties may be defined in future documents.  These future
   properties will be represented by RRsets directly below the name of a
   member node.

   Implementations and operators of catalog zones may choose to provide
   their own properties.  To prevent a name clash with future
   properties, private properties should be represented below the label
   ext.<unique-N>.zones.$CATZ. ext is not a placeholder, so a custom
   property would have the domain name <your-label>.ext.<unique-

6.  Nameserver Behavior

6.1.  General Requirements

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

   Although they are regular DNS zones, catalog zones contain only
   information for the management of a set of authoritative nameservers.
   For this reason, operators may want to limit the systems able to
   query these zones.  It may be inconvenient to serve some contents of
   catalog zones via DNS queries anyway due to the nature of their
   representation.  A separate method of querying entries inside the
   catalog zone may be made available by nameserver implementations (see
   Section 7).

   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.

   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 catalog consumer to

van Dijk, et al.          Expires 28 April 2022                [Page 10]
Internet-Draft              dns-catalog-zones               October 2021

   synchronize catalog zones from the primary, but the primary's
   administrators may not have any administrative access to the

   Nameservers MAY allow loading and transfer of broken zones with
   incorrect catalog zone syntax (as they are treated as regular zones),
   but catalog consumers MUST NOT process such broken zones as catalog
   zones.  For the purpose of catalog processing, the broken catalogs
   MUST be ignored.

6.2.  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 {#cooproperty}.

6.3.  Member zone removal

   When a member zone is removed from a specific catalog zone, an
   authoritative server 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

6.4.  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 6.3), immediately followed by processing the member as a
   newly to be configured zone in the same catalog.

6.5.  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 5.1.  Otherwise a
   migration of 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.

van Dijk, et al.          Expires 28 April 2022                [Page 11]
Internet-Draft              dns-catalog-zones               October 2021

   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 down time or otherwise),
   but did already see the update of $NEWCATZ, they may consider the
   update adding the member zone in $NEWCATZ to be a name clash (see
   Section 6.2) 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

6.6.  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 6.4).

7.  Implementation Notes

   Catalog zones on secondary nameservers would have to be setup
   manually, perhaps as static configuration, similar to how ordinary
   DNS zones are configured.  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
   synchronized of the member zones for secondary service.

   An administrator may want to look at data inside a catalog zone.
   Typical queries might include dumping the list of 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 multi-valued
   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.

van Dijk, et al.          Expires 28 April 2022                [Page 12]
Internet-Draft              dns-catalog-zones               October 2021

8.  Security Considerations

   As catalog zones are transmitted using DNS zone transfers, it is
   RECOMMENDED that catalog zone transfer 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 [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 the consumers of the catalog
   zone.  It is RECOMMENDED to limit the systems able to query these
   zones.  It is RECOMMENDED to transfer catalog zones confidentially

   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.

   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 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 6.6) before or
   simultaneously with adding the coo property.

9.  IANA Considerations

9.1.  SERIAL RR type

   This document defines a new DNS RR type, SERIAL, in the "Resource
   Record (RR) TYPEs" subregistry of the "Domain Name System (DNS)
   Parameters" registry:

van Dijk, et al.          Expires 28 April 2022                [Page 13]
Internet-Draft              dns-catalog-zones               October 2021

        | TYPE   | Value | Meaning                   | Reference |
        | SERIAL | TBD   | Version number of the     | [this     |
        |        |       | original copy of the zone | document] |

                                 Table 1

10.  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.

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

   Thanks to Brian Conry, Tony Finch, Evan Hunt, Patrik Lundin, Victoria
   Risk, Carsten Strotmann, and Kees Monshouwer for reviewing draft
   proposals and offering comments and suggestions.

   Thanks to Klaus Darilion who came up with the idea for the serial
   property during the hackathon at the IETF-109.  Thanks also to Shane
   Kerr, Petr Spacek, Brian Dickson for further brainstorming and
   discussing the serial property and how it would work best with
   catalog zones.

11.  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, <>.

van Dijk, et al.          Expires 28 April 2022                [Page 14]
Internet-Draft              dns-catalog-zones               October 2021

   [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,

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

   [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,

12.  Informative References

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

Appendix A.  Implementation Status

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

   In the following implementation status descriptions, "DNS Catalog
   Zones" refers to DNS Catalog Zones as described in this document.

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

van Dijk, et al.          Expires 28 April 2022                [Page 15]
Internet-Draft              dns-catalog-zones               October 2021

   *  PowerDNS has a proof of concept external program called PowerCATZ
      (, that can process DNS
      Catalog Zones.

   *  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.

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

Appendix B.  Change History (to be removed before final publication)

   *  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

van Dijk, et al.          Expires 28 April 2022                [Page 16]
Internet-Draft              dns-catalog-zones               October 2021

   |  Remove Open issues and discussion Appendix, which was about zone
   |  options (including primary/secondary relationships) only.

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

   |  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

van Dijk, et al.          Expires 28 April 2022                [Page 17]
Internet-Draft              dns-catalog-zones               October 2021

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

Authors' Addresses

   Peter van Dijk
   Den Haag


   Libor Peltan


van Dijk, et al.          Expires 28 April 2022                [Page 18]
Internet-Draft              dns-catalog-zones               October 2021

   Ondrej Sury
   Internet Systems Consortium


   Willem Toorop
   NLnet Labs
   Science Park 400
   1098 XH Amsterdam


   Leo Vandewoestijne


   Peter Thomassen
   deSEC, Secure Systems Engineering


van Dijk, et al.          Expires 28 April 2022                [Page 19]