The complete multicast architecture defined today in different RFCs and Internet Drafts is described in this section. It is very important to know all the different address types defined because the allocation mechanisms will depend of the architecture used.

RFC 3513 (IP Version 6 Addressing Architecture) defines the IPv6 multicast address. As shown in Table 8-1, IPv6 multicast addresses are derived from the FF00::/8 prefix. The octet following the initial obligatory “FF” value contains four flags and 4-bit value defining the scope of the multicast group.

The flags field is a set of 4 flag bits.

Only bit T is described in RFC 3513 and indicates if the address is permanent (value 0) or temporary (value 1). Bits P and R are described in RFC 3306 [RFC3306] and RFC 3956 [RFC3956]. The high order flag bit is not yet used. The use of the flags makes it possible to distinguish different address type that will be detailed in the following sections.

The meaning of the 4-bit scope value is summarized in Table 8-3.