http://www.rfc-editor.org/rfc/rfc1112.txt
RFC 1112: Host extensions for IP multicasting, S.E. Deering1989-08-01T23:00:00-00:00This memo specifies the extensions required of a host implementation of the Internet Protocol (IP) to support multicasting. Recommended procedure for IP multicasting in the Internet. This RFC obsoletes RFCs 998 and 1054. [STANDARDS-TRACK]