IdIPMCastBase.pas contains constants, records, types, and classes needed to implement the ancestor for classes that support IP multicasting, as described in the Internet Standards documents:
RFC 1112 - Host Extensions for IP Multicasting (http://www.rfc-editor.org/rfc/rfc1112.txt)
RFC 1458 - Requirements for Multicast Protocols (http://www.rfc-editor.org/rfc/rfc1458.txt)