The domain-name type represents a DNS domain name. The
name SHOULD be fully qualified whenever possible.
Internet domain names are only loosely specified. Section
3.5 of RFC 1034 recommends a syntax (modified in Section
2.1 of RFC 1123). The pattern above is intended to allow
for current practice in domain name use, and some possible
future expansion. It is designed to hold various types of
domain names, including names used for A or AAAA records
(host names) and other records, such as SRV records. Note
that Internet host names have a stricter syntax (described
in RFC 952) than the DNS recommendations in RFCs 1034 and
1123, and that systems that want to store host names in
schema nodes using the domain-name type are recommended to
adhere to this stricter standard to ensure interoperability.
The encoding of DNS names in the DNS protocol is limited
to 255 characters. Since the encoding consists of labels
prefixed by a length bytes and there is a trailing NULL
byte, only 253 characters can appear in the textual dotted
notation.
The description clause of schema nodes using the domain-name
type MUST describe when and how these names are resolved to
IP addresses. Note that the resolution of a domain-name value
may require to query multiple DNS records (e.g., A for IPv4
and AAAA for IPv6). The order of the resolution process and
which DNS record takes precedence can either be defined
explicitly or may depend on the configuration of the
resolver.
Domain-name values use the US-ASCII encoding. Their canonical
format uses lowercase US-ASCII characters. Internationalized
domain names MUST be A-labels as per RFC 5890.
RFC 952: DoD Internet Host Table Specification
RFC 1034: Domain Names - Concepts and Facilities
RFC 1123: Requirements for Internet Hosts -- Application
and Support
RFC 2782: A DNS RR for specifying the location of services
(DNS SRV)
RFC 5890: Internationalized Domain Names in Applications
(IDNA): Definitions and Document Framework