Editing IPv6 (section)

===Multicasting===
[[File:IPv6 multicast address stracture-en.svg|thumb|Multicast structure in IPv6]]
[[Multicast]]ing, the transmission of a packet to multiple destinations in a single send operation, is part of the base specification in IPv6. In IPv4 this is an optional (although commonly implemented) feature.{{Ref RFC|1112}} IPv6 multicast addressing has features and protocols in common with IPv4 multicast, but also provides changes and improvements by eliminating the need for certain protocols. IPv6 does not implement traditional [[Broadcast IP address|IP broadcast]], i.e. the transmission of a packet to all hosts on the attached link using a special ''broadcast address'', and therefore does not define broadcast addresses. In IPv6, the same result is achieved by sending a packet to the link-local ''all nodes'' multicast group at address {{IPaddr|ff02::1}}, which is analogous to IPv4 multicasting to address {{IPaddr|224.0.0.1}}. IPv6 also provides for new multicast implementations, including embedding rendezvous point addresses in an IPv6 multicast group address, which simplifies the deployment of inter-domain solutions.{{Ref RFC|3956}}

In IPv4 it is very difficult for an organization to get even one globally routable multicast group assignment, and the implementation of inter-domain solutions is arcane.{{Ref RFC|2908}} Unicast address assignments by a [[local Internet registry]] for IPv6 have at least a 64-bit routing prefix, yielding the smallest subnet size available in IPv6 (also 64 bits). With such an assignment it is possible to embed the unicast address prefix into the IPv6 multicast address format, while still providing a 32-bit block, the least significant bits of the address, or approximately 4.2 billion multicast group identifiers. Thus each user of an IPv6 subnet automatically has available a set of globally routable source-specific multicast groups for multicast applications.{{Ref RFC|3306}}