Internet Engineering Task Force (IETF) P. van Dijk

Internet Engineering Task Force (IETF) P. van Dijk
Request for Comments: 9432 PowerDNS
Category: Standards Track L. Peltan
ISSN: 2070-1721 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
July 2023

DNS Catalog Zones

Abstract

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

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9432.

Copyright Notice

Copyright (c) 2023 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
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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. Terminology
3. Description
4. Catalog Zone Structure
4.1. Member Zones
4.2. Properties
4.2.1. Schema Version (version property)
4.3. Member Zone Properties
4.3.1. Change of Ownership (coo property)
4.3.2. Groups (group property)
4.4. Custom Properties (*.ext properties)
5. Name Server Behavior
5.1. General Requirements
5.2. Member Zone Name Clash
5.3. Member Zone Removal
5.4. Member Node Name Change
5.5. Migrating Member Zones between Catalogs
5.6. Zone-Associated State Reset
6. Implementation and Operational Notes
7. Security Considerations
8. IANA Considerations
9. References
9.1. Normative References
9.2. Informative References
Appendix A. Catalog Zone Example
Acknowledgements
Authors' Addresses

1. Introduction

The content of a DNS zone is synchronized among its primary and
secondary name servers using Authoritative Transfer (AXFR) and
Incremental Zone Transfer (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 name server farm has to not only add or remove
the zone from the primary but must also add or remove configuration
for the zone from all secondaries. This can be both inconvenient and
error-prone. In addition, the steps required are dependent on the
name server 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
name servers just like any other zone. Secondary name servers can
then add, remove, or modify the zones they serve in accordance with
the changes to the catalog zone. Other use cases of name server
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",
"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.

Catalog zone: A DNS zone containing a DNS catalog, which 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
zone.

$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).

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

3. Description

A catalog zone is a DNS zone whose contents are specially crafted.
Its resource records (RRs) 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 name servers, a catalog zone is a regular DNS zone and must
adhere to the standards for DNS zones.

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

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.

The names of member zones are represented on the RDATA side of a PTR
record (instead of being represented as a part of owner names) 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 that MUST NOT be processed
(see Section 5.1).

For example, if a catalog zone lists three zones ("example.com.",
"example.net.", and "example.org."), the member node RRs would appear
as follows:

<unique-1>.zones.$CATZ 0 IN PTR example.com.
<unique-2>.zones.$CATZ 0 IN PTR example.net.
<unique-3>.zones.$CATZ 0 IN PTR example.org.

where <unique-N> is a label that tags each record in the collection
and has a unique value. 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
ignored.

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 that have the correct RR type but 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).

This document includes a set of initial properties that 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 that 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"; that is:

version.$CATZ 0 IN TXT "2"

Note that Version 1 was used in an earlier draft version of this memo
and reflected the implementation first found in BIND 9.11.

4.3. Member Zone Properties

Each member zone MAY have one or more additional properties that are
described in this section. 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 "example.com." migrates from catalog
zone $OLDCATZ to catalog zone $NEWCATZ, this will appear in the
$OLDCATZ catalog zone as follows:

<unique-N>.zones.$OLDCATZ 0 IN PTR example.com.
coo.<unique-N>.zones.$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 that
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.
Before the actual migration, the consumer MUST verify that the 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 the zone-associated
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
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.

4.3.2. Groups (group property)

With a group property, a 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
configuration.

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 a 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.

4.3.2.1. Example

group properties are represented by TXT RRs. 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 catalog.

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) that
signals to a consumer(s) how to treat DNSSEC for the zones
"example.net." and "example.com.":

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

In this scenario, a consumer(s) shall, by agreement, not sign the
member zone "example.com." with DNSSEC. For "example.net.", the
consumers, at two different operators, will configure the member zone
to be signed with a specific combination of settings. The group
value designated to indicate this combination of settings is
prearranged 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 globally or for a
specific member zone. To prevent a name clash with future
properties, such properties MUST be represented below the label
"ext".

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

; a global custom property:
<property-prefix>.ext.$CATZ

; a member zone custom property:
<property-prefix>.ext.<unique-N>.zones.$CATZ

<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-
setting>.<implementation-name>.ext.$CATZ.

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

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
override 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
interoperability.

5. Name Server Behavior

5.1. General Requirements

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

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

Name servers 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,
it loses its catalog meaning because of an update through an
incremental transfer or otherwise. 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
zone.

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

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 (from either an
existing member zone or an 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 it 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. The zone
and associated state (such as zone data and DNSSEC keys) MUST be
removed from the consumer when and only when the zone was configured
initially from the same catalog. Consumer operators may consider
temporarily archiving associated state to facilitate mistake
recovery.

5.4. Member Node Name Change

When the member node's label value (<unique-N>) changes via a single
update or transfer, catalog consumers MUST process this as a member
zone removal, including the removal of all the zone's associated
state (as described in Section 5.3), and then immediately process the
member as a newly added zone to be configured 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, the
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 and then 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
already saw the update of $NEWCATZ containing the addition of that
member zone, they may consider this update 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. For example, it may 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
$OLDCATZ.

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 a domain name under a suitable name such as
"invalid." [RFC6761].

Catalog zones on secondary name servers 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. Additionally, the
secondary 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 only contain
information for the management of a set of authoritative name
servers. 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. Therefore, an
administrator may want to use a different method for looking at data
inside the 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 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 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 be protected from unexpected
modifications by way of authentication, e.g., by using a Transaction
Signature (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 name servers for a
catalog zone may be operated by different administrators. The
secondary name servers 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
secondaries.

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, a 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 has created the "DNS Catalog Zones Properties" registry under
the "Domain Name System (DNS) Parameters" registry 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 [RFC8126].

Reference: RFC 9432

Note: This registry applies to Catalog Zones schema version "2" as
specified in RFC 9432.

+=================+======================+===========+===========+
| Property Prefix | Description | Status | Reference |
+=================+======================+===========+===========+
| zones | List of member zones | Standards | RFC 9432 |
| | | Track | |
+-----------------+----------------------+-----------+-----------+
| version | Schema version | Standards | RFC 9432 |
| | | Track | |
+-----------------+----------------------+-----------+-----------+
| coo | Change of Ownership | Standards | RFC 9432 |
| | | Track | |
+-----------------+----------------------+-----------+-----------+
| group | Group | Standards | RFC 9432 |
| | | Track | |
+-----------------+----------------------+-----------+-----------+
| *.ext | Custom properties | Private | RFC 9432 |
| | | Use | |
+-----------------+----------------------+-----------+-----------+

Table 1: DNS Catalog Zones Properties Registry

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
property.

Status: IETF Stream RFC status or "External" if not documented in an
IETF Stream RFC.

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

9. References

9.1. Normative References

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.

[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
August 1996, <https://www.rfc-editor.org/info/rfc1996>.

[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/info/rfc2119>.

[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,
<https://www.rfc-editor.org/info/rfc2136>.

[RFC2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, DOI 10.17487/RFC2606, June 1999,
<https://www.rfc-editor.org/info/rfc2606>.

[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.

[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/info/rfc8174>.

[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.

[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,
<https://www.rfc-editor.org/info/rfc8945>.

[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,
<https://www.rfc-editor.org/info/rfc9103>.

9.2. Informative References

[FOSDEM20] Vandewoestijne, L., "Extending Catalog zones - another
approach in automating maintenance", February 2020,
<https://archive.fosdem.org/2020/schedule/event/
dns_catz/>.

[Metazones]
Vixie, P., "Federated Domain Name Service Using DNS
Metazones", DOI 10.1093/ietcom/e89-b.4.1144, April 2006,
<https://www.semanticscholar.org/paper/Federated-Domain-
Name-Service-Using-DNS-Metazones-Vixie/
dc12b0116332f5c236b05c71bbe20499f3c6c4b6>.

[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/info/rfc8126>.

Appendix A. Catalog Zone Example

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

catalog.invalid. 0 SOA invalid. (
invalid. 1625079950 3600 600 2147483646 0 )
catalog.invalid. 0 NS invalid.
example.vendor.ext.catalog.invalid. 0 CNAME example.net.
version.catalog.invalid. 0 TXT "2"
nj2xg5b.zones.catalog.invalid. 0 PTR example.com.
nvxxezj.zones.catalog.invalid. 0 PTR example.net.
group.nvxxezj.zones.catalog.invalid. 0 TXT (
"operator-x-foo" )
nfwxa33.zones.catalog.invalid. 0 PTR example.org.
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 (
collector.example.net. )

Acknowledgements

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

Catalog zones originated as the chosen method among various proposals
that were evaluated at Internet Systems Consortium (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 they 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 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
earlier draft versions and offering comments and suggestions.

Authors' Addresses

Peter van Dijk
PowerDNS
Den Haag
Netherlands
Email: [email protected]

Libor Peltan
CZ.NIC
Czech Republic
Email: [email protected]

Ondrej Sury
Internet Systems Consortium
Czech Republic
Email: [email protected]

Willem Toorop
NLnet Labs
Science Park 400
1098 XH Amsterdam
Netherlands
Email: [email protected]

Kees Monshouwer
Netherlands
Email: [email protected]

Peter Thomassen
deSEC, SSE - Secure Systems Engineering
Berlin
Germany
Email: [email protected]

Aram Sargsyan
Internet Systems Consortium
Email: [email protected]