| Internet Engineering Task Force | M. Sivaraman |
| Internet-Draft | S. Morris |
| Intended status: Experimental | R. Bellis |
| Expires: September 2, 2018 | W. Krecicki |
| Internet Systems Consortium | |
| March 1, 2018 |
DNS Catalog Zones
draft-muks-dnsop-dns-catalog-zones-04
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 will also be 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 6.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
A catalog zone is a specially crafted DNS zone that contains, as DNS zone data:
An implementation of catalog zones MAY allow the catalog to contain other catalog zones as member zones, but default zone configuration present in a catalog zone only applies to its immediate 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 one or more NS records 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.
Since there is no requirement to be able to query the catalog zone via recursive namservers the NS records at the apex will not be used and no parent delegation is required. However, they are still required so that catalog zones are syntactically correct DNS zones. Any valid DNS name can be used in the NSDNAME field of such NS records [RFC1035] and they MUST be ignored. A single NS RR with an NSDNAME field containing the absolute name "invalid." is RECOMMENDED [RFC2606].
A catalog zone contains a set of key/value pairs, where each key is encapsulated within the owner name of a DNS RR and the corresponding value is stored in the RR's RDATA. The specific owner name depends on whether the property relates to the catalog zone itself, a member zone thereof, or to default zone properties described in Section 4.3. The owner names are case insensitive.
Each key/value pair has a defined data type, and each data type accordingly uses a particular RR TYPE to represent its possible values, as specified in Section 5.
The general form of a catalog zone record is as follows:
[<unique-id>.]<key>.<path>.$CATZ 0 IN <RRTYPE> <value>
where <path> is a sequence of labels with values depending on the purpose (and hence position) of the record within the catalog zone (see Section 4.3) and where the <unique-id> prefix is only present for multi-valued properties (see Section 4.2.2).
NB: Catalog zones use some RR TYPEs (such as PTR) with alternate semantics to those originally defined for them. Although this may be controversial, the situation is similar to other similar zone-based representations such as response-policy zones [RPZ].
The CLASS field of every RR in a catalog zone MUST be IN (1). This is because some RR TYPEs such as APL used by catalog zones are defined only for the IN class.
The TTL field's value is not specially defined by this memo. Catalog zones are for authoritative nameserver management only and are not intended for general querying via recursive resolvers and therefore a value of zero (0) is RECOMMENDED.
It is an error for any single owner name within a catalog zone (other than the apex of the zone itself) to have more than one RR associated with it.
Some properties do not represent single values but instead represent a collection of values. The specification for each property describes whether it is single-valued or multi-valued. A multi-valued property is encoded as multiple RRs where the owner name of each individual RR contains a unique (user specified) DNS label.
So, while a single-valued key might be represented like this:
<key>.<path>.$CATZ IN TXT "value"
a multi-valued key would be represented like this:
<unique-id-1>.<key>.<path>.$CATZ IN TXT "value 1"
<unique-id-2>.<key>.<path>.$CATZ IN TXT "value 2"
...
NB: a property that is specified to be multi-valued MUST be encoded using the unique prefixed key syntax even if there is only one value present.
The specification of any multi-valued property MUST document whether the collection represents either an ordered or un-ordered list. In the former case the ordering of the prefixes according to the usual DNS canonical name ordering will determine the sort order.
TBD: Prepare a list of zone configuration properties that are common to DNS implementations. This is so that a company may manage a catalog zone using a Windows DNS server as the primary, and a secondary nameserver hosting service may pick up the common properties and may use a different nameserver implementation such as BIND or NSD on a POSIX operating system to serve it.
TBD: We may specify that unrecognized zone property names must be ignored, or that nameserver specific properties must be specified using the "x-" prefix similar to MIME type naming.
TBD: Any list of zone properties is ideally maintained as a registry rather than within this memo.
The list of member zones is specified as a multi-valued 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.$CATZ 0 IN PTR example.org.
where <m-unique-N> is a label that uniquely tags each record in the collection, as described in Section 4.2.2.
Although any legal label could be used for <m-unique-N> it is RECOMMENDED that it be a value deterministically derived from the fully-qualified member zone name. The BIND9 implementation uses the 40 character hexadecimal representation of the SHA-1 digest [FIPS.180-4.2015] of the lower-cased member zone name as encoded in uncompressed wire format.
The catalog zone schema version is specified by an unsigned integer property with the property name "version". All catalog zones MUST have this property present. Primary and secondary nameservers MUST NOT use catalog zones with an unexpected value in this property, but they may be transferred as ordinary zones. For this memo, the "version" property value MUST be set to 2, i.e.
version.$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.
Default zone configuration comprises a set of properties that are applied to all member zones listed in the catalog zone unless overridden my member zone-specific information.
All such properties are stored as child nodes of the owner name "defaults" itself a direct child node of the catalog zone, e.g.:
example-prop.defaults.$CATZ 0 IN TXT "Example"
Default zone properties can be overridden on a per-zone basis by specifying the property under the the sub-domain associated with the member zone in the list of zones, e.g.:
example-prop.<m-unique>.zones.$CATZ 0 IN TXT "Example"
where "m-unique" is the label that uniquely identifies the member zone name as described in Section 4.3.1.
NB: when a zone-specific property is multi-valued the owner name will contain two unique identifiers, the left-most tagging being associated with the individual value (<unique-id-N>) and the other (<m-unique>) associated with the member zone itself, e.g.:
$ORIGIN <m-unique>.zones.$CATZ
<unique-id-1>.example-prop 0 IN TXT "Value 1"
<unique-id-2>.example-prop 0 IN TXT "Value 2"
...
This section lists the various data types defined for use within catalog zones.
A key with a string value is represented with a TXT RR [RFC1035], e.g.:
example-prop.<m-unique>.zones.$CATZ 0 IN TXT "Example"
If the RDATA is split into multiple <character-string> elements the MUST be directly concatenated without any separating character.
A key with a boolean value is represented with a TXT RR containing a single <character-string> with a value of "true" for true condition and "false" for false condition, e.g:
example-prop.<m-unique>.zones.$CATZ 0 IN TXT "false"
The RDATA is case-insensitive.
A key with an integer value is specified using a TXT RR containing a single <character-string>.
A signed integer's TXT RDATA uses the representation of an unsuffixed "integer constant" as defined in the C programming language standard [ISO.9899.1990] (of the type matching a 64-bit signed integer on that platform), with an optional minus prefix.
An unsigned integer's TXT RDATA uses the representation of an unsuffixed "integer constant" as defined in the C programming language standard [ISO.9899.1990] (of the type matching a 64-bit unsigned integer on that platform).
For example, a property with an unsigned integer value of 300 would appear as follows:
example-prop.<m-unique>.zones.$CATZ 0 IN TXT "300"
A key with a floating-point value is specified using a TXT RR containing a single <character-string>.
A floating-point value's TXT RDATA uses the representation of an unsuffixed "floating constant" as defined in the C programming language standard [ISO.9899.1990].
For example, a property with an unsigned integer value of 0.15 may appear as follows:
example-prop.<m-unique>.zones.$CATZ 0 IN TXT "15e-2"
A key whose value is a domain name is specified using a PTR RR [RFC1035], e.g.:
example-prop.defaults.$CATZ 0 IN PTR ns1.example.com.
A property whose value is an IP network prefix is specified using an APL RR [RFC3123]. The negation flag ("!" in presentation format) may be used to indicate all addresses not included within that prefix, e.g. for use in Access Control Lists, e.g.:
Although a single APL record is capable of containing multiple prefixes, for consistency of representation lists of prefixes MUST use the multi-valued property syntax as documented in Section 4.2.2, e.g.:
$ORIGIN <m-unique>.zones.$CATZ
<unique-id-1>.example-prop 0 IN APL ( 1:192.0.2.0/24 )
<unique-id-2>.example-prop 0 IN APL ( !1:0.0.0.0/0 )
Implementations MUST accept only the first prefix within each APL record and MUST ignore any subsequent prefixes found therein.
A single host address is represented using either an A or AAAA record as appropriate, e.g.:
example-prop1.<m-unique>.zones.$CATZ 0 IN A 192.0.2.1
example-prop2.<m-unique>.zones.$CATZ 0 IN AAAA 2001:db8::1
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 6.3).
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.
TBD: Transitive primary-secondary relationships
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.
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.
We later 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. |
| [RPZ] | Vixie, P. and V. Schryver, "DNS Response Policy Zones (DNS RPZ)", 2010. |