| Internet-Draft | dns-catalog-zones | October 2021 |
| van Dijk, et al. | Expires 28 April 2022 | [Page] |
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 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.¶
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.¶
$CATZ$OLDCATZ and $NEWCATZ are used to discuss migration a member zone from one catalog zone $OLDCATZ to another catalog zone $NEWCATZ.¶
A catalog zone is a DNS zone whose contents are specially crafted. Its records primarily constitute a list of PTR records referencing other DNS zones (so-called "member zones"). The catalog zone may contain other records indicating additional metadata (so-called "properties") associated with these member zones.¶
Catalog consumers SHOULD ignore any RR in the catalog zone which is meaningless or useless to the implementation.¶
Authoritative servers may be preconfigured with multiple catalog zones, each associated with a different set of configurations.¶
Although the contents of a catalog zone are interpreted and acted upon by nameservers, a catalog zone is a regular DNS zone and so must adhere to the standards for such zones.¶
A catalog zone is primarily intended for the management of a farm of authoritative nameservers. The content of catalog zones may not be accessible from any recursive nameserver.¶
As with any other DNS zone, a catalog zone MUST have a syntactically correct SOA record and at least one NS record at its apex.¶
The SOA record's SERIAL, REFRESH, RETRY and EXPIRE fields [RFC1035] are used during zone transfer. A catalog zone's SOA SERIAL field MUST increase when an update is made to the catalog zone's contents as per serial number arithmetic defined in [RFC1982]. Otherwise, catalog consumers might not notice updates to the catalog zone's contents.¶
There is no requirement to be able to query the catalog zone via recursive nameservers. Catalog consumers MUST ignore and MUST NOT assume or require NS records at the apex. However, at least one is still required so that catalog zones are syntactically correct DNS zones. A single NS RR with a NSDNAME field containing the absolute name "invalid." is RECOMMENDED [RFC2606].¶
The catalog zone schema version is specified by an integer value embedded in a TXT RR named version.$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", i.e.¶
version.$CATZ 0 IN TXT "2"¶
NB: Version 1 was used in a draft version of this memo and reflected the implementation first found in BIND 9.11.¶
The list of member zones is specified as a collection of member nodes, represented by domain names under the owner name "zones" where "zones" is a direct child domain of the catalog zone.¶
The names of member zones are represented on the RDATA side (instead of as a part of owner names) of a PTR record, so that all valid domain names may be represented regardless of their length [RFC1035]. This PTR record MUST be the only record in the PTR RRset with the same name. More than one record in the RRset denotes a broken catalog zone which MUST NOT be processed (see Section 6.1).¶
For example, if a catalog zone lists three zones "example.com.", "example.net." and "example.org.", the member node RRs would appear as follows:¶
<unique-1>.zones.$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.
<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).¶
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.¶
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 node.¶
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 "example.com." 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 example.com. 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.¶
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 $OLDCATZ once it has been established that all its consumers have processed the Change of Ownership.¶
With a group property, consumer(s) can be signalled to treat some member zones within the catalog zone differently.¶
The consumer MAY apply different configuration options when processing member zones, based on the value of the group property.
The exact handling of configuration referred to by the group property value is left to the consumer's implementation and configuration.
The property is defined by a TXT record in the sub-node labelled group.¶
The producer MAY assign a group property to all, some, or none of the member zones within a catalog zone.
The producer MUST NOT assign more than one group property to one member zone.¶
The consumer MUST ignore either all or none of the group properties in a catalog zone.¶
The value of the TXT record MUST be at most 255 octets long and MUST NOT contain whitespace characters. The consumer MUST interpret the value case-sensitively.¶
<unique-1>.zones.$CATZ 0 IN PTR example.com. group.<unique-1>.zones.$CATZ 0 IN TXT sign-with-nsec3 <unique-2>.zones.$CATZ 0 IN PTR example.net. 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.¶
By generating the catalog zone (snippet) above, the producer signals how the consumer shall treat DNSSEC for the zones example.net. and example.com., respectively.¶
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.¶
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]¶
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.¶
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 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).¶
The presentation format of the RDATA portion is as follows:¶
The Serial fields is represented as an unsigned decimal integer.¶
The serial property of a member zone is provided by a SERIAL RRset with a
single SERIAL RR named serial.<unique-N>.zones.$CATZ.¶
For example, if a catalog zone lists three zones "example.com.", "example.net."
and "example.org.", and a serial property is provided for each of them, the
RRs would appear as follows:¶
<unique-1>.zones.$CATZ 0 IN PTR example.com. serial.<unique-1>.zones.$CATZ 0 IN SERIAL 3 <unique-2>.zones.$CATZ 0 IN PTR example.net. serial.<unique-2>.zones.$CATZ 0 IN SERIAL 1634730530 <unique-3>.zones.$CATZ 0 IN PTR example.org. serial.<unique-3>.zones.$CATZ 0 IN SERIAL 2020112405¶
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.$CATZ.
ext is not a
placeholder, so a custom property would have the domain name <your-label>.ext.<unique-N>.zones.$CATZ¶
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 synchronize catalog zones from the primary, but the primary's administrators may not have any administrative access to the secondaries.¶
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.¶
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}.¶
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 removed.¶
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.¶
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.¶
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 $OLDCATZ.¶
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).¶
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.¶
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 [RFC9103].¶
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.¶
This document defines a new DNS RR type, SERIAL, in the "Resource Record (RR) TYPEs" subregistry of the "Domain Name System (DNS) Parameters" registry:¶
| TYPE | Value | Meaning | Reference |
|---|---|---|---|
| SERIAL | TBD | Version number of the original copy of the zone | [this document] |
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, 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.¶
Note to the RFC Editor: please remove this entire section before publication.¶
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.¶
PowerDNS has a proof of concept external program called PowerCATZ, that can process DNS Catalog Zones.¶
Proof of concept python scripts 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.¶
Initial public draft.¶
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.¶
Addressed some review comments by Patrik Lundin.¶
Revision bump.¶
Reordering of sections into more logical order. Separation of multi-valued properties into their own category.¶
New authors to pickup the editor pen on this draft¶
Remove data type definitions for zone properties Removing configuration of member zones through zone properties altogether¶
Remove Open issues and discussion Appendix, which was about zone options (including primary/secondary relationships) only.¶
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.¶
Adding the
cooproperty for zone migration in a controlled fashion¶Adding the
groupproperty for reconfigure settings of member zones in an atomic update¶Adding the
epochproperty to reset zone associated state in a controlled fashion¶
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¶
Move Implementation status to appendix¶
Miscellaneous textual improvements¶
cooproperty points to$NEWCATZ(and notzones.$NEWCATZ)¶Remove suggestion to increase serial and remove member zone from
$OLDCATZafter 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
serialproperty¶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
epochproperty. 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¶