DNSOP Working Group                                          P. van Dijk
Internet-Draft                                                  PowerDNS
Intended status: Standards Track                               L. Peltan
Expires: October 16, 2020                                         CZ.NIC
                                                                 O. Sury
                                             Internet Systems Consortium
                                                               W. Toorop
                                                              NLnet Labs
                                                       L. Vandewoestijne
                                                          April 14, 2020

                           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
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   This Internet-Draft will expire on October 16, 2020.

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   Copyright (c) 2020 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
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   publication of this document.  Please review these documents

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Catalog Zone Structure  . . . . . . . . . . . . . . . . . . .   4
     4.1.  SOA and NS Records  . . . . . . . . . . . . . . . . . . .   4
     4.2.  Catalog Zone Schema Version . . . . . . . . . . . . . . .   4
     4.3.  List of Member Zones  . . . . . . . . . . . . . . . . . .   4
   5.  Nameserver Behavior . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  General Requirements  . . . . . . . . . . . . . . . . . .   5
   6.  Updating Catalog Zones  . . . . . . . . . . . . . . . . . . .   7
     6.1.  Implementation Notes  . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Appendix A.  Change History (to be removed before final
                publication) . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The data in 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, the changes are propagated 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 zone.

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   The contents and representation of catalog zones are described in
   Section 3.  Nameserver behavior is described in Section 5.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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, that is, a list of DNS zones.

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

      Used in examples as a placeholder to represent the domain name of
      the catalog zone itself (c.f. $ORIGIN).

3.  Description

   A catalog zone is a specially crafted DNS zone that contains, as DNS
   zone data:

   o  A list of DNS zones (called "member zones").

   Implementations of catalog zones 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.  A
   member zone can as such be reconfigured with a different set of
   preconfigured settings by removing it as a member of one catalog zone
   and making it a member of another.

   An implementation of catalog zones MAY allow the catalog to contain
   other catalog zones as member zones.

   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.  It is not expected that the content of
   catalog zones will be accessible from any recursive nameserver.

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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,
   secondary nameservers might not notice updates to the catalog zone's

   Should the zone be made available for querying, the SOA record's
   MINIMUM field's value is the negative cache time (as defined in
   [RFC2308]).  Since recursive nameservers are not expected to be able
   to access (and subsequently cache) entries from a catalog zone a
   value of zero (0) is RECOMMENDED.

   There is no requirement to be able to query the catalog zone via
   recursive nameservers.  Implementations of catalog zones 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 an NSDNAME field containing
   the absolute name "invalid." is RECOMMENDED [RFC2606].

4.2.  Catalog Zone Schema Version

   The catalog zone schema version is specified by an integer value
   embeded in a TXT RR named "version.$CATZ".  All catalog zones MUST
   have a TXT RRset named "version.$CATZ" with at least one RR.  Primary
   and secondary nameservers MUST NOT use catalog 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", 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.

4.3.  List of Member Zones

   The list of member zones is specified as a collection of 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) so that all valid domain names may be
   represented regardless of their length [RFC1035].

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

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

   where "<m-unique-N>" is a label that uniquely tags each record in the

   Having a large number of member zones in a single RRset may cause the
   RRset to be too large to be conveyed via DNS messages which make up a
   zone transfer.  Having the zones uniquely tagged with the "<m-unique-
   N>" label ensures the list of member zones can be split over multiple
   DNS messages in a zone transfer.

   The "<m-unique-N>" label also enables the state for a zone to be
   reset. (see Section 6) As long as no zone state needs to be reset at
   the authoritative nameservers, the unique label associated with a
   zone SHOULD remain the same.

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

   The TTL field's value is not specially defined by this memo.  Catalog
   zones are for authoritative nameserver management only and are not
   intended for general querying via recursive resolvers and therefore a
   value of zero (0) is RECOMMENDED.

   It is an error for any single owner name within a catalog zone (other
   than the apex of the zone itself) to have more than one RR associated
   with it.

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.

   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

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   representation.  A separate method of querying entries inside the
   catalog zone may be made available by nameserver implementations (see
   Section 6.1).

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

   A catalog zone can be updated via DNS UPDATE on a reference primary
   nameserver, or via zone transfers.  Nameservers MAY allow loading and
   transfer of broken zones with incorrect catalog zone syntax (as they
   are treated as regular zones), but nameservers MUST NOT process such
   broken zones as catalog zones.  For the purpose of catalog
   processing, the broken catalogs MUST be ignored.  If a broken catalog
   zone was transferred, the newly transferred catalog zone MUST be
   ignored (but the older copy of the catalog zone SHOULD be left
   running subject to values in SOA fields).

   If there is a clash between an existing member zone's name 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.

   When zones are introduced into a catalog zone, a primary SHOULD first
   make the new zones available for transfers before making the updated
   catalog zone available for transfer, or sending NOTIFY for the
   catalog zone to secondaries.  Note that secondary nameservers may
   attempt to transfer the catalog zone upon refresh timeout, so care
   must be taken to make the member zones available before any update to
   the list of member zones is visible in the catalog zone.

   When zones are deleted from a catalog zone, a primary MAY delete the
   member zone immediately after notifying secondaries.  It is up to the
   secondary nameserver to handle this condition correctly.

   When the "<m-unique-N>" label of a member zone changes, all its
   associated state MUST be reset, including the zone itself.  This can
   be relevant for example when zone ownership is changed.  In that case
   one does not want the new owner to inherit the metadata.  Other
   situations might be resetting DNSSEC state, or forcing a new zone
   transfer.  A simple removal followed by an addition of the member
   zone would be insufficient for this purpose because it is infeasible

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   for secondaries to track, due to missed notifies or being offline
   during the removal/addition.

6.  Updating Catalog Zones

   TBD: Explain updating catalog zones using DNS UPDATE.

6.1.  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.  Members of such catalog zones will be
   automatically synchronized by the secondary after the catalog zone is

   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.

7.  Security Considerations

   As catalog zones are transmitted using DNS zone transfers, it is
   absolutely essential for these transfers to be protected from
   unexpected modifications on the route.  So, catalog zone transfers
   SHOULD be authenticated using TSIG [RFC2845].  A primary nameserver
   SHOULD NOT serve a catalog zone for transfer without using TSIG and a
   secondary nameserver SHOULD abandon an update to a catalog zone that
   was received without using TSIG.

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

   Zone transfers of member zones SHOULD similarly be authenticated
   using TSIG [RFC2845].  The TSIG shared secrets used for member zones
   MUST NOT be mentioned anywhere in the catalog zone data.  However,
   key identifiers may be shared within catalog zones.

   Catalog zones do not need to be signed using DNSSEC, their zone
   transfers being authenticated by TSIG.  Signed zones MUST be handled

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   normally by nameservers, and their contents MUST NOT be DNSSEC-

8.  IANA Considerations

   This document has no IANA actions.

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.

   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 and Carsten Strettman for reviewing draft proposals and offering
   comments and suggestions.

10.  References

10.1.  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,

   [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,

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   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,

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

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,

   [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>.

10.2.  Informative References

              Vixie, P., "Federated Domain Name Service Using DNS
              Metazones", 2005, <http://ss.vix.su/~vixie/mz.pdf>.

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

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

      Initial public draft.

   o  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.

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

      Addressed some review comments by Patrik Lundin.

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

      Revision bump.

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

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

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

      New authors to pickup the editor pen on this draft

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

      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.

Authors' Addresses

   Peter van Dijk
   Den Haag

   Email: peter.van.dijk@powerdns.com

   Libor Peltan

   Email: libor.peltan@nic.cz

   Ondrej Sury
   Internet Systems Consortium

   Email: ondrej@isc.org

   Willem Toorop
   NLnet Labs
   Science Park 400
   Amsterdam  1098 XH

   Email: willem@nlnetlabs.nl

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   Leo Vandewoestijne

   Email: leo@dns.company

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