| 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
draft-toorop-dnsop-dns-catalog-zones-01
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.
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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.
The contents and representation of catalog zones are described in Section 3. Nameserver behavior is described in Section 5.
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.
A catalog zone is a specially crafted DNS zone that contains, as DNS zone data:
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.
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 contents.
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].
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.$CATZ 0 IN TXT "2"
NB: Version 1 was used in a draft version of this memo and reflected the implementation first found in BIND 9.11.
The list of member zones is specified as a collection of domain names under the owner name "zones" where "zones" is a direct child domain of the catalog zone.
The names of member zones are represented on the RDATA side (instead of as a part of owner names) so that all valid domain names may be represented regardless of their length [RFC1035].
For example, if a catalog zone lists three zones "example.com.", "example.net." and "example.org.", the RRs would appear as follows:
<m-unique-1>.zones.$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 collection.
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.
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 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 for secondaries to track, due to missed notifies or being offline during the removal/addition.
TBD: Explain updating catalog zones using DNS UPDATE.
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 configured.
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.
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 normally by nameservers, and their contents MUST NOT be DNSSEC- validated.
This document has no IANA actions.
Our deepest thanks and appreciation go to Stephen Morris, Ray Bellis and Witold Krecicki who initiated this draft and did the bulk of the work.
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.
| [Metazones] | Vixie, P., "Federated Domain Name Service Using DNS Metazones", 2005. |