Information Technology Reference
In-Depth Information
The type of an IPv6 address can be determined by the high-order bits. The number of bits
used to determine an address's type is variable. This set of high-order bits is also called the
format prefix. The primary divisions of the IPv6 address space are shown in Table 12-2.
Table 12-2
IPv6 Address Space
Address Type
Binary Prefix
IPv6 Notation
Unspecified
00...0 (128 bits)
::/128
Loopback
00...1 (128 bits)
::1/128
Multicast
11111111
FF00::/8
Link-local unicast
1111111010
FE80::/10
Site-local unicast
1111111011
FEC0::/10
Global unicast
(Everything else)
—
Anycast addressing is taken from global unicast addressing and is no different from a
unicast address syntactically.
Aggregatable Global Unicast Addresses
The term
aggregatable global unicast addresses
is really just a fancy term for normal
unicast addressing using a globally routable prefix. Until recently, there was a complex
hierarchical structure for aggregating global unicast addresses based on Top-Level
Aggregators (TLAs), Next-Level Aggregators (NLAs), and Site-Level Aggregators
(SLAs). However, this structure was recently deprecated by RFC 3587.
Local Addressing
IPv6 has two types of local addressing: link-local and site-local. Link-local addressing was
designed to be used on a single link, which might be a point-to-point connection with only
two hosts or a broadcast medium with hundreds of hosts. Packets containing a source or
destination address with link-local scope are not to be forwarded to another subnet. The
purpose of link-local addressing is to provide local connectivity, address autoconfiguration,
and neighbor discovery on networks without a router present. The format of a link-local
address is shown in Figure 12-2.
Figure 12-2
Link-Local Addressing Format
