Network Working Group M. Davids Internet-Draft SIDN Labs Intended status: Best Current Practice 11 April 2025 Expires: 13 October 2025 Registration of Underscored and Globally Scoped DNS Node Name: "_for- sale" draft-davids-forsalereg-04 Abstract This document defines an operational convention for using the reserved DNS node name "_for-sale" to indicate that the parent domain name is available for purchase. This approach offers the advantage of easy deployment without affecting ongoing operations. As such, the method can be applied to a domain name that is still in full use. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 13 October 2025. Copyright Notice Copyright (c) 2025 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Davids Expires 13 October 2025 [Page 1] Internet-Draft forsalereg April 2025 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Content limitations . . . . . . . . . . . . . . . . . . . 3 3.2. RRset limitations . . . . . . . . . . . . . . . . . . . . 4 3.3. RR Type limitations . . . . . . . . . . . . . . . . . . . 4 3.4. TTL limitation . . . . . . . . . . . . . . . . . . . . . 4 3.5. Wildcard limitation . . . . . . . . . . . . . . . . . . . 4 3.6. CNAME limitation . . . . . . . . . . . . . . . . . . . . 4 3.7. Placement of node name . . . . . . . . . . . . . . . . . 4 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Example 1: A URI . . . . . . . . . . . . . . . . . . . . 5 4.2. Example 2: Various other approaches . . . . . . . . . . . 5 5. Operational Guidelines . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Implementation Status . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 11.2. Informative References . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Well-established services [RFC3912][RFC9083] exist to determine whether a domain name is registered. However, the fact that a domain name exists does not necessarily mean it is unavailable; it may still be for sale. Some registrars and other entities offer mediation services between domain name holders and interested parties; however, for domain names not for sale, such services may be unnecessary. This specification defines a simple and universal method to ascertain whether a domain name, although registered, is available for purchase. It enables a domain name holder to add a reserved underscored node name [RFC8552] in the zone, indicating that the domain name is for sale. The TXT RR type [RFC1035] that is created for that purpose MAY contain a pointer, such as a Uniform Resource Identifier (URI) [RFC8820], allowing interested parties to obtain information or contact the domain name holder for further negotiations. Davids Expires 13 October 2025 [Page 2] Internet-Draft forsalereg April 2025 With due caution, such information can also be incorporated into automated availability services. When a domain name is checked for availability, the service can indicate whether it is for sale and provide a pointer to the seller's information. 1.1. Terminology 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. 2. Rationale There are undoubtedly more ways to address this problem space. The reasons for the approach defined in this document are primarily accessibility and simplicity. The indicator can be easily turned on and off at will and moreover, it is immediately deployable and does not require significant changes in existing services. This allows for a smooth introduction of the concept. 3. Conventions 3.1. Content limitations The TXT [RFC8553] (Section 2.1) record MUST contain any valid content, ranging from an empty string to meaningful text or URIs. However, it SHALL NOT contain any text that suggests that the domain is not for sale. If a domain name is not for sale, the "_for-sale" indicator MUST NOT be used. Any existence of a "_for-sale" TXT record, assuming it is not a wildcard, MAY therefore be regarded as an indication that the domain name is for sale. This specification does not dictate the exact use of any content in the "_for-sale" TXT record, or the lack of any such content. Parties - such as registries and registrars - may use it in their tools, perhaps even by defining additional requirements that the content must meet. Alternatively, an individual can use it in combination with existing tools to make contact with the seller. The content of the TXT record is "as is" and characters such as ";" between two URIs for example, have no defined meaning. It is up to the processor of the content to decide how to handle it. See Section 5 for additional guidelines. Davids Expires 13 October 2025 [Page 3] Internet-Draft forsalereg April 2025 3.2. RRset limitations This specification does not define any restrictions on the number of TXT records in the RRset, although it is recommended to limit it to one. It is also recommended that the length of the RDATA [RFC8499] does not exceed 255 bytes. If the RRset contains multiple records or the total size exceeds 255 bytes, it is up to the processor to determine which data to use. For example, a registry might pick a mandatory URI from the RRset to display on a website as part of its service, while an individual might just pick a phone number (if present) and dial it to make contact with a potential seller. 3.3. RR Type limitations Adding any other RR types under the "_for-sale" leaf but TXT is not recommended and they MUST be ignored for the purpose of this document. 3.4. TTL limitation A TTL longer than 86400 is NOT RECOMMENDED. Long TTLs increase the risk of outdated information persisting, potentially misleading buyers into believing the domain is still available for purchase. 3.5. Wildcard limitation The "_for-sale" leaf SHOULD NOT be a wildcard. 3.6. CNAME limitation The "_for-sale" leaf MAY be a CNAME pointing to a TXT RR type. 3.7. Placement of node name The "_for-sale" leaf node name MAY be placed on the top level domain, or any domain directly below. It MAY also be placed at a lower level, but only when that level is mentioned in the Public Suffix List [PSL]. Any other placement of the record MUST NOT be regarded as a signal that the domain above it is for sale. See Table 1 for further explanation. Davids Expires 13 October 2025 [Page 4] Internet-Draft forsalereg April 2025 +============================+====================+==========+ | Name | Situation | Verdict | +============================+====================+==========+ | _for-sale.example | root zone | For sale | +----------------------------+--------------------+----------+ | _for-sale.aaa.example | Second level | For sale | +----------------------------+--------------------+----------+ | _for-sale.acme.bbb.example | bbb.example in PSL | For sale | +----------------------------+--------------------+----------+ | _for-sale.www.ccc.example | Other | Invalid | +----------------------------+--------------------+----------+ Table 1: Allowed placements of TXT record 4. Examples 4.1. Example 1: A URI The holder of 'example.com' wishes to signal that the domain is for sale and adds this record to the 'example.com' zone: _for-sale.example.com. IN TXT "https://broker.example.net/offer?id=3" An interested party notices this signal and can visit the URI mentioned for further information. The TXT record can also be processed by automated tools, but see the Security Considerations section for possible risks. As an alternative, a mailto: URI could also be used: _for-sale.example.com. IN TXT "mailto:owner@example.com" Or a telephone URI: _for-sale.example.com. IN TXT "tel:+1-201-555-0123" There can be a use case for these URIs, especially since WHOIS (or RDAP) often has privacy restrictions. But see the Privacy Considerations section for possible downsides. 4.2. Example 2: Various other approaches Free format text, to make the availability more explicit: _for-sale.example.com. IN TXT "I'm for sale: info [at] example.com" Davids Expires 13 October 2025 [Page 5] Internet-Draft forsalereg April 2025 Proprietary format, used by a registry or registrar to automatically redirect visitors to a web page, but which has no well-defined meaning to third parties: _for-sale.example.com. IN TXT "fscode=aHR0cHM...V4YW1wbGUuY29t" The content in the following example could be malicious, but it is not in violation of this specification (see Section 8): _for-sale.example.com. IN TXT "" 5. Operational Guidelines DNS wildcards interact poorly with underscored names, which is why the use of wildcards is NOT RECOMMENDED when deploying this mechanism. But they may still be encountered in practice, especially by operators who are not deploying this mechanism. Therefore, any assumptions about the content of "_for-sale" TXT records should be made with caution. For instance, some operators configure wildcards to return a fixed "v=spf1 -all" TXT record for all subdomains. In such cases, the presence of a "_for-sale" TXT record containing this content does not indicate that the domain is actually for sale. To minimize confusion, it is RECOMMENDED to include content that is recognizable either by humans or automated systems, such as the "fscode=" string or the descriptive text shown in the Examples section. As an alternative. the situation can be circumvented by adding a "_for-sale" leaf node with a different RR type, anything other than TXT. Although being an exception to the recommendations, it will prevent confusing wildcard responses to TXT queries. For example: _for-sale.example.com. IN HINFO "NOT A TXT" "NOT FOR SALE" In general it is best to avoid the above wildcard situation completely. 6. IANA Considerations IANA has established the "Underscored and Globally Scoped DNS Node Names" registry [RFC8552][IANA]. The underscored node name defined in this specification should be added as follows: Davids Expires 13 October 2025 [Page 6] Internet-Draft forsalereg April 2025 +-----------+--------------+-------------+ | RR Type | _NODE NAME | Reference | +-----------+--------------+-------------+ | TXT | _for-sale | TBD | +-----------+--------------+-------------+ Figure 1: Entry for the "Underscored and Globally Scoped DNS Node Names" registry 7. Privacy Considerations The use of the "_for-sale" node name publicly indicates the intent to sell a domain name. Domain owners should be aware that this information is accessible to anyone querying the DNS and may have privacy implications. There is a risk of data scraping, such as email addresses and phone numbers. 8. Security Considerations One use of the TXT record type defined in this document is to parse the content it contains and to automatically publish certain information from it on a website or elsewhere. However, there is a risk if the domain name holder publishes a malicious URI or one that points to improper content. This may result in reputational damage for the party parsing the record. Even worse is a scenario in which the content of the TXT record is not validated and sanitized sufficiently, opening doors to - for example - XSS attacks among other things. Therefore, it is RECOMMENDED that any parsing and publishing is conducted with the utmost care. There is also a risk that this method will be abused as a marketing tool, or to otherwise lure individuals into visiting certain sites or attempting other forms of contact, without there being any intention to actually sell the particular domain name. Therefore, it is recommended that this method is primarily used by professionals. 9. Implementation Status The concept described in this document is in use with the .nl ccTLD registry. See for example: https://www.sidn.nl/en/whois?q=example.nl Davids Expires 13 October 2025 [Page 7] Internet-Draft forsalereg April 2025 [_note to editor: please remove this section before publication_] 10. Acknowledgements The author would like to thank Thijs van den Hout, Caspar Schutijser, Melvin Elderman and Paul Bakker for their valuable feedback. 11. References 11.1. Normative References [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8552] Crocker, D., "Scoped Interpretation of DNS Resource Records through "Underscored" Naming of Attribute Leaves", BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019, . 11.2. Informative References [IANA] IANA, "Underscored and Globally Scoped DNS Node Names", . [PSL] Mozilla Foundation, "Public Suffix List", . [RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912, DOI 10.17487/RFC3912, September 2004, . [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Terminology", RFC 8499, DOI 10.17487/RFC8499, January 2019, . Davids Expires 13 October 2025 [Page 8] Internet-Draft forsalereg April 2025 [RFC8553] Crocker, D., "DNS Attrleaf Changes: Fixing Specifications That Use Underscored Node Names", BCP 222, RFC 8553, DOI 10.17487/RFC8553, March 2019, . [RFC8820] Nottingham, M., "URI Design and Ownership", BCP 190, RFC 8820, DOI 10.17487/RFC8820, June 2020, . [RFC9083] Hollenbeck, S. and A. Newton, "JSON Responses for the Registration Data Access Protocol (RDAP)", STD 95, RFC 9083, DOI 10.17487/RFC9083, June 2021, . Author's Address Marco Davids SIDN Labs Meander 501 6825 MD Arnhem Netherlands Phone: +31 26 352 5500 Email: marco.davids@sidn.nl Davids Expires 13 October 2025 [Page 9]