| Internet-Draft | Announce Parent DNS Scanner | September 2025 |
| Bergström, et al. | Expires 6 March 2026 | [Page] |
In DNS operations, automated scanners are commonly employed by the operator of a parent zone to detect the presence of specific records, such as CDS or CSYNC, in child zones, indicating a desire for delegation updates. However, the presence and periodicity of these scanners are typically implicit and undocumented, leading to inefficiencies and uncertainties. ¶
This document proposes an extension to the semantics of the DSYNC resource record, as defined in draft-ietf-dnsop-generalized-notify, allowing parent zones to explicitly signal the presence and scanning interval of such automated scanners. This enhancement aims to improve transparency and coordination between child and parent zones.¶
TO BE REMOVED: This document is being collaborated on in Github at: https://github.com/johanix/draft-berra-dnsop-announce-scanner. The most recent working version of the document, open issues, etc, should all be available there. The authors (gratefully) accept pull requests.¶
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Automated scanners play a vital role in DNS operations by monitoring zones for specific records that signal desired updates to delegation information. For instance, the presence of CDS records in a child zone indicates a request to update DS records in the parent zone. However, the operation of these scanners is often opaque, with no standardized method for parent zones to signal their presence or scanning frequency. ¶
The lack of explicit signaling can lead to inefficiencies, such as unnecessary scanning or delayed updates due to misaligned expectations between child and parent zones. To address this, this document proposes an extension to the semantics of the DSYNC resource record, enabling parent zones to explicitly announce the presence and scanning interval of their automated scanners.¶
As the DSYNC record becomes standard automated child-side systems looking up the parent DSYNC records are expected. Given that a vast majority of parent zones do not operate scanners providing a simple mechaism to inform the child of this fact will be useful.¶
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].¶
The DSYNC resource record, as defined in [I-D.draft-ietf-dnsop-generalized-notify], facilitates the discovery of endpoints for generalized NOTIFY messages. This document proposes a new {scheme} for this record that can be used to signal scanner presence (or absence) and periodicity. This new scheme=3 is defined as "SCANNER".¶
The DSYNC record has the following format, as defined in [I-D.draft-ietf-dnsop-generalized-notify]:¶
{owner} IN DSYNC {RRtype} {Scheme} {Port} {Target}¶
For scanner signaling, the fields are interpreted as follows:¶
owner: The name of the parent zone. Follows the discovery methods specified in the DSYNC specification.¶
RRtype: The type of record the scanner is monitoring (e.g., CDS, CSYNC).¶
Scheme: Set to SCANNER (on the wire this is represented as a uint8 = 3).¶
Port: Overloaded to represent the scanning interval in minutes.¶
Target: Not used, RECOMMENDED to set to ".".¶
To signal the presence of a scanner that check for CDS and CSYNC records once every 24 hours, a parent zone would publish the following DSYNC records:¶
_dsync.parent.example. IN DSYNC CDS SCANNER 1440 . _dsync.parent.example. IN DSYNC CSYNC SCANNER 1440 .¶
The presence of these records informs the child operator that the parent zone operates a scanner for both CDS and CSYNC records with a 1440-minute (= 24h) interval.¶
To explicitly signal the absence of a scanner, the parent zone would set the port field to 0:¶
_dsync.parent.example. IN DSYNC CDS SCANNER 0 . _dsync.parent.example. IN DSYNC CSYNC SCANNER 0 .¶
The presence of these records indicate that the parent zone does not operate a scanner for CDS or CSYNC records.¶
Parent zones can also use the wildcard and child-specific methods to signal the presence or absence of scanners as described in [I-D.draft-ietf-dnsop-generalized-notify].¶
For example:¶
*._dsync.parent.example. IN DSYNC CDS SCANNER 0 . *._dsync.parent.example. IN DSYNC CSYNC SCANNER 0 .¶
or¶
child._dsync.parent.example. IN DSYNC CDS SCANNER 0 . child._dsync.parent.example. IN DSYNC CSYNC SCANNER 0 .¶
Publishing DSYNC records (typically for both CDS and CSYNC records) requires no coordination between parent and child zones. The parent zone operator should ensure that the DSYNC records accurately reflect their scanner operations (or absence of a scanner). Child zone operators may use this information to adjust their expectations and processes accordingly.¶
It's important to note that overloading the port field for scanner interval signaling deviates from its original purpose. Using a new {scheme}, "SCANNER", is intended to minimize the implications of this as software implementations SHOULD discard any unsupported schemes.¶
The proposed new DSYNC scheme does not introduce new security vulnerabilities. As in [I-D.draft-ietf-dnsop-generalized-notify] use of DNSSEC is RECOMMENDED but not required. Hence, a child service that looks up DSYNC RRsets in the parent zone may choose to ignore unsigned DSYNC RRsets.¶
IANA is requested to assign a new "scheme" value to the registry for "DSYNC Location of Synchronization Endpoints" as follows:¶
Reference (this document)¶
+========+========+==========+======================+=================+ | RRtype | Scheme | Mnemonic | Purpose | Reference | +========+========+==========+======================+=================+ | CDS | 3 | SCANNER | Scanner announcement | (this document) | +--------+--------+----------+----------------------+-----------------+ | CSYNC | 3 | SCANNER | Scanner announcement | (this document) | +--------+--------+----------+----------------------+-----------------+¶
Initial public draft Make sure examples use _dsync label and propose new scheme¶