3Com 4500G Family Configuration Manual page 303

Anycast address: An identifier for a set of interfaces (typically belonging to different nodes). A
packet sent to an anycast address is delivered to one of the interfaces identified by that address
(the target interface is nearest to the source, according to a routing protocol's measure of
distance).
There are no broadcast addresses in IPv6. Their function is replaced by multicast addresses.
The type of an IPv6 address is designated by the first several bits called format prefix.
mappings between address types and format prefixes.
Table 1-1 Mappings between address types and format prefixes
Type
Unassigned address
Loopback address
Unicast
Link-local address
address
Site-local address
Global unicast
address
Multicast address
Anycast address
Unicast address
There are several types of unicast addresses, including aggregatable global unicast address, link-local
address, and site-local address.
The aggregatable global unicast addresses, equivalent to public IPv4 addresses, are provided for
network service providers. This type of address allows efficient prefix aggregation to restrict the
number of global routing entries.
The link-local addresses are used for communication between link-local nodes in neighbor
discovery and stateless autoconfiguration. Packets with link-local source or destination addresses
are not forwarded to other links.
IPv6 unicast site-local addresses are similar to private IPv4 addresses. Packets with site-local
source or destination addresses are not forwarded out of the local site (a private network).
Loopback address: The unicast address 0:0:0:0:0:0:0:1 (represented in the shortest format as ::1)
is called the loopback address and may never be assigned to any physical interface. Like the
loopback address in IPv4, it may be used by a node to send an IPv6 packet to itself.
Unassigned address: The unicast address "::" is called the unassigned address and may not be
assigned to any node. Before acquiring a valid IPv6 address, a node may fill this address in the
source address field of an IPv6 packet. It cannot be used as a destination IPv6 address.
Format prefix (binary)
00...0 (128 bits)
00...1 (128 bits)
1111111010
1111111011
other forms
11111111
Anycast addresses are taken from unicast address space and
are not syntactically distinguishable from unicast addresses.
1-4
Table 1-1 lists the
IPv6 prefix ID
::/128
::1/128
FE80::/10
FEC0::/10
—
FF00::/8