used for documentation as described in Section 3.1.8. The multicast addresses can be recognized from the leading 8 bits of an IPv6 address, which are always ff as listed in Figure 3.6 and defined in RFC 4291 [4]. The flag bits, the 4 bits following the leading ff as illustrated in Figure 3.11, tell about the properties of the address. The 'T'-bit indicates whether the address is perma- nently assigned by IANA (value '0') or dynamically assigned address (value '1'). Bit 'P', however, has a more significant meaning: whether the address is based on a network prefix (value '1') or address is not based on a network prefix (value '0') [52]. As shown in Table 3.1, the IANA assigned addresses have all flag bits as zero, hence indicating permanently assigned and not network prefix based addresses. The dynamic addresses can be created by an end host or by an allocation server, using the prefixes they have at their disposal, based on a need for a temporary (but possibly long-lived) multicast group. If the 'P' bit has a value of '1', the 'group identifier', which identifies a multicast group and for which the basic address format reserves 112 bits, is given more detailed structure as is illustrated in Figure 3.12. The group identifier field is split into 8 bits of reserved space, 8 bits for prefix length, 64 bits for the network prefix, and the 32 remaining bits for the actual group identifier. For example, a unicast address prefix, such as 2001 db8 cafe /48, is mapped into the multicast prefix by setting the 'plen' field to '0x30' (decimal 48) and the network prefix to 2001: db8 cafe: 0000, thus resulting in a multicast IPv6 address prefix of ff3x: 0030:2001 db8 cafe: : /96, where the 'X' denotes a selected scope. If the R bit is set to one, the multicast address contains an address of a rendezvous point. This is realized by using four bits of the reserved-field shown in Figure 3.12 to transport rendezvous point's interface identifier [161]. Multicast addressing utilizes scoping system to limit the distribution of packets s