3Com MSR 50 Series Configuration Manual page 658

658 C 46: IP 6 B
HAPTER V ASICS
n
C
ONFIGURATION
Unicast address: An identifier for a single interface, similar to an IPv4 unicast
■
address. A packet sent to a unicast address is delivered to the interface
identified by that address.
Multicast address: An identifier for a set of interfaces (typically belonging to
■
different nodes), similar to an IPv4 multicast address. A packet sent to a
multicast address is delivered to all interfaces identified by that address.
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 nearest one, according to the routing
protocols' measure of distance).
There are no broadcast addresses in IPv6. Their function is superseded by multicast
addresses.
The type of an IPv6 address is designated by the first several bits called format
prefix. Table 36 lists the mappings between address types and format prefixes.
Table 36 Mapping between address types and format prefixes
Type
Unicast Unassigned address
address
Loopback address
Link-local address
Site-local address
Global unicast
address
Multicast address
Anycast address
Unicast address
There are several forms of unicast address assignment in IPv6, including
aggregatable global unicast address, link-local address, and site-local address.
The aggregatable global unicast address, equivalent to an IPv4 public address,
■
is provided for network service providers. This type of address allows efficient
route prefix aggregation to restrict the number of global routing entries.
The link-local address is used for communication between link-local nodes in
■
neighbor discovery and stateless autoconfiguration. Routers must not forward
any packets with link-local source or destination addresses to other links.
IPv6 unicast site-local addresses are similar to private IPv4 addresses. Routers
■
must not forward any packets with site-local source or destination addresses
outside of the site (equivalent to 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
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.
IPv6 prefix ID
::/128
::1/128
FE80::/10
FEC0::/10
-
FF00::/8