http://www.rfc-editor.org/rfc/rfc1219.txt
RFC 1219: On the assignment of subnet numbers, P.F. Tsuchiya1991-04-01T23:00:00-00:00This memo suggests a new procedure for assigning subnet numbers. Use of this assignment technique within a network would be a purely local matter, and would not effect other networks. This memo provides information for the Internet community. It does not specify an Internet standard.