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The ALT Special Use Top Level Domain (draft)draft-ietf-dnsop-alt-tld-21 (24 February 2023)
This document reserves a TLD label, "alt" to be used in non-DNS contexts. It also provides advice and guidance to developers developing alternative namespaces.
Many Internet protocols need to name entities. Names that look like DNS names (a series of labels separated with dots) have become common, even in systems that are not part of the global DNS administered by IANA. This document reserves the top-level label "alt" (short for "alternative") as a special-use domain name ([RFC6761]). This top-level label can be used as the final (rightmost) label to signify that the name is not rooted in the global DNS, and that it should not be resolved using the DNS protocol.
In Section 3.1, the IANA is requested to add the .alt name to the "Special-Use Domain Name" registry. IANA sets aside names in that registry, as described in <https://www.iana.org/domains/reserved>.
Throughout the rest of this document, the top-level "alt" label is shown as ".alt" to match the common presentation form of DNS names.
The techniques in this document are primarily intended to address some of the issues discussed in [RFC8244], which contains additional background on the issues with special use domain names.
In this document, ".alt" was chosen for the special-use domain name instead of something like "alt.arpa" so that systems that use the name do not have to worry that a parent of their name would be resolved if the name leaked to the Internet. Historically, some systems that want to use non-DNS names wanted the entire name to be not in the DNS, and reserving ".alt" fulfills that use case.