http://www.rfc-editor.org/rfc/rfc4608.txt
RFC 4608: Source-Specific Protocol Independent Multicast in 232/8, D. Meyer, R. Rockell, G. Shepherd2006-08-01T23:00:00-00:00IP Multicast group addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast destination addresses and are reserved for use by source-specific multicast applications and protocols. This document defines operational recommendations to ensure source-specific behavior within the 232/8 range. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.