http://www.rfc-editor.org/rfc/rfc1101.txt
RFC 1101: DNS encoding of network names and other types, P.V. Mockapetris1989-04-01T23:00:00-00:00This RFC proposes two extensions to the Domain Name System: - A specific method for entering and retrieving RRs which map between network names and numbers. - Ideas for a general method for describing mappings between arbitrary identifiers and numbers. The method for mapping between network names and addresses is a proposed standard, the ideas for a general method are experimental.