IPv6 Supported Address Types
One important change in the addressing model of IPv6 is the address types supported.
IPv4 supported three address types: unicast, multicast, and broadcast. Of these,
the vast majority of actual traffic was unicast. IP multicast support was not widely
deployed until many years after the Internet was established and it continues to be
hampered by various issues. Use of broadcast in IP had to be severely restricted for
performance reasons (we don’t want any device to be able to broadcast across the
IPv6 also supports three address types, but with the following changes:
Unicast Addresses These are standard unicast addresses as in IPv4, one per host
Multicast Addresses These are addresses that represent various groups of IP
devices. A message sent to a multicast address goes to all devices in the group. IPv6
includes much better multicast features and many more multicast addresses than
IPv4. Since multicast under IPv4 was hampered in large part due to lack of support
of the feature by many hardware devices,
support for multicasting is a required, not
optional, part of IPv6.
Anycast Addresses Anycast addressing is used when a message must be sent to any
member of a group, but does not need to be sent to all of them. Usually the member
of the group that is easiest to reach will be sent the message. One common
example of how anycast addressing could be used is in load sharing among a group
of routers in an organization.
Broadcast addressing as a distinct addressing method is gone in IPv6. Broadcast
functionality is implemented using multicast addressing to groups of devices. A
multicast group to which all nodes belong can be used for broadcasting in a network,
KEY CONCEPT IPv6 has unicast and multicast addresses like IPv4. There is, however, no
distinct concept of a broadcast address in IPv6. A new type of address, the anycast address, has
been added to allow a message to be sent to any one member of a group of devices.