<s>
An	O
Internet	B-Protocol
Protocol	I-Protocol
Version	I-Protocol
6	I-Protocol
address	O
(	O
IPv6	B-Protocol
address	I-Protocol
)	O
is	O
a	O
numeric	O
label	O
that	O
is	O
used	O
to	O
identify	O
and	O
locate	O
a	O
network	O
interface	B-Protocol
of	O
a	O
computer	O
or	O
a	O
network	B-Protocol
node	I-Protocol
participating	O
in	O
a	O
computer	B-Architecture
network	I-Architecture
using	O
IPv6	B-Protocol
.	O
</s>
<s>
IP	B-Protocol
addresses	I-Protocol
are	O
included	O
in	O
the	O
packet	O
header	O
to	O
indicate	O
the	O
source	O
and	O
the	O
destination	O
of	O
each	O
packet	O
.	O
</s>
<s>
The	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
destination	O
is	O
used	O
to	O
make	O
decisions	O
about	O
routing	B-Protocol
IP	B-Protocol
packets	I-Protocol
to	O
other	O
networks	O
.	O
</s>
<s>
IPv6	B-Protocol
is	O
the	O
successor	O
to	O
the	O
first	O
addressing	O
infrastructure	O
of	O
the	O
Internet	O
,	O
Internet	B-Protocol
Protocol	I-Protocol
version	I-Protocol
4	I-Protocol
(	O
IPv4	B-Protocol
)	O
.	O
</s>
<s>
In	O
contrast	O
to	O
IPv4	B-Protocol
,	O
which	O
defined	O
an	O
IP	B-Protocol
address	I-Protocol
as	O
a	O
32-bit	O
value	O
,	O
IPv6	B-Protocol
addresses	I-Protocol
have	O
a	O
size	O
of	O
128	O
bits	O
.	O
</s>
<s>
Therefore	O
,	O
in	O
comparison	O
,	O
IPv6	B-Protocol
has	O
a	O
vastly	O
enlarged	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
IPv6	B-Protocol
addresses	I-Protocol
are	O
classified	O
by	O
the	O
primary	O
addressing	O
and	O
routing	B-Protocol
methodologies	O
common	O
in	O
networking	O
:	O
unicast	B-Protocol
addressing	O
,	O
anycast	B-Protocol
addressing	O
,	O
and	O
multicast	O
addressing	O
.	O
</s>
<s>
A	O
unicast	B-Protocol
address	I-Protocol
identifies	O
a	O
single	O
network	O
interface	B-Protocol
.	O
</s>
<s>
The	O
Internet	O
Protocol	O
delivers	O
packets	O
sent	O
to	O
a	O
unicast	B-Protocol
address	I-Protocol
to	O
that	O
specific	O
interface	B-Protocol
.	O
</s>
<s>
An	O
anycast	B-Protocol
address	O
is	O
assigned	O
to	O
a	O
group	O
of	O
interfaces	O
,	O
usually	O
belonging	O
to	O
different	O
nodes	O
.	O
</s>
<s>
A	O
packet	O
sent	O
to	O
an	O
anycast	B-Protocol
address	O
is	O
delivered	O
to	O
just	O
one	O
of	O
the	O
member	O
interfaces	O
,	O
typically	O
the	O
nearest	O
host	O
,	O
according	O
to	O
the	O
routing	B-Protocol
protocol	O
's	O
definition	O
of	O
distance	O
.	O
</s>
<s>
Anycast	B-Protocol
addresses	O
cannot	O
be	O
identified	O
easily	O
,	O
they	O
have	O
the	O
same	O
format	O
as	O
unicast	B-Protocol
addresses	O
,	O
and	O
differ	O
only	O
by	O
their	O
presence	O
in	O
the	O
network	O
at	O
multiple	O
points	O
.	O
</s>
<s>
Almost	O
any	O
unicast	B-Protocol
address	I-Protocol
can	O
be	O
employed	O
as	O
an	O
anycast	B-Protocol
address	O
.	O
</s>
<s>
A	O
multicast	B-Protocol
address	I-Protocol
is	O
also	O
used	O
by	O
multiple	O
hosts	O
that	O
acquire	O
the	O
multicast	B-Protocol
address	I-Protocol
destination	O
by	O
participating	O
in	O
the	O
multicast	O
distribution	O
protocol	O
among	O
the	O
network	B-Protocol
routers	I-Protocol
.	O
</s>
<s>
A	O
packet	O
that	O
is	O
sent	O
to	O
a	O
multicast	B-Protocol
address	I-Protocol
is	O
delivered	O
to	O
all	O
interfaces	O
that	O
have	O
joined	O
the	O
corresponding	O
multicast	O
group	O
.	O
</s>
<s>
IPv6	B-Protocol
does	O
not	O
implement	O
broadcast	O
addressing	O
.	O
</s>
<s>
However	O
,	O
the	O
use	O
of	O
the	O
all-nodes	O
group	O
is	O
not	O
recommended	O
,	O
and	O
most	O
IPv6	B-Protocol
protocols	O
use	O
a	O
dedicated	O
link-local	O
multicast	O
group	O
to	O
avoid	O
disturbing	O
every	O
interface	B-Protocol
in	O
the	O
network	O
.	O
</s>
<s>
An	O
IPv6	B-Protocol
address	I-Protocol
consists	O
of	O
128	O
bits	O
.	O
</s>
<s>
For	O
each	O
of	O
the	O
major	O
addressing	O
and	O
routing	B-Protocol
methodologies	O
,	O
various	O
address	O
formats	O
are	O
recognized	O
by	O
dividing	O
the	O
128	O
address	O
bits	O
into	O
bit	O
groups	O
and	O
using	O
established	O
rules	O
for	O
associating	O
the	O
values	O
of	O
these	O
bit	O
groups	O
with	O
special	O
addressing	O
features	O
.	O
</s>
<s>
Unicast	B-Protocol
and	O
anycast	B-Protocol
addresses	O
are	O
typically	O
composed	O
of	O
two	O
logical	O
parts	O
:	O
a	O
64-bit	O
network	O
prefix	O
used	O
for	O
routing	B-Protocol
,	O
and	O
a	O
64-bit	O
interface	B-Protocol
identifier	O
used	O
to	O
identify	O
a	O
host	O
's	O
network	O
interface	B-Protocol
.	O
</s>
<s>
The	O
network	O
prefix	O
(	O
the	O
routing	B-Protocol
prefix	O
combined	O
with	O
the	O
subnet	O
id	O
)	O
is	O
contained	O
in	O
the	O
most	O
significant	O
64	O
bits	O
of	O
the	O
address	O
.	O
</s>
<s>
The	O
size	O
of	O
the	O
routing	B-Protocol
prefix	O
may	O
vary	O
;	O
a	O
larger	O
prefix	O
size	O
means	O
a	O
smaller	O
subnet	O
id	O
size	O
.	O
</s>
<s>
The	O
64-bit	O
interface	B-Protocol
identifier	O
is	O
automatically	O
established	O
randomly	O
,	O
obtained	O
from	O
a	O
DHCPv6	B-Protocol
server	O
,	O
or	O
assigned	O
manually	O
.	O
</s>
<s>
(	O
Historically	O
,	O
it	O
was	O
automatically	O
generated	O
from	O
the	O
interface	B-Protocol
's	O
MAC	O
address	O
using	O
the	O
modified	O
EUI-64	O
format	O
,	O
but	O
this	O
method	O
is	O
now	O
deprecated	O
for	O
privacy	O
reasons	O
.	O
)	O
</s>
<s>
Unique	O
local	O
addresses	O
are	O
addresses	O
analogous	O
to	O
IPv4	B-Protocol
private	B-Protocol
network	I-Protocol
addresses	O
.	O
</s>
<s>
+	O
Unique	B-Protocol
local	I-Protocol
address	I-Protocol
formatbits	O
7	O
1	O
40	O
16	O
64field	O
prefix	O
L	O
random	O
subnet	O
id	O
interface	B-Protocol
identifierThe	O
prefix	O
field	O
contains	O
the	O
binary	O
value	O
1111110	O
.	O
</s>
<s>
The	O
L	O
bit	O
is	O
one	O
for	O
locally	O
assigned	O
addresses	O
;	O
the	O
address	B-General_Concept
range	I-General_Concept
with	O
L	O
set	O
to	O
zero	O
is	O
currently	O
not	O
defined	O
.	O
</s>
<s>
The	O
random	O
field	O
is	O
chosen	O
randomly	O
once	O
,	O
at	O
the	O
inception	O
of	O
the	O
routing	B-Protocol
prefix	O
.	O
</s>
<s>
A	O
link-local	B-Protocol
address	I-Protocol
is	O
also	O
based	O
on	O
the	O
interface	B-Protocol
identifier	O
,	O
but	O
uses	O
a	O
different	O
format	O
for	O
the	O
network	O
prefix	O
.	O
</s>
<s>
The	O
54	O
zeroes	O
that	O
follow	O
make	O
the	O
total	O
network	O
prefix	O
the	O
same	O
for	O
all	O
link-local	O
addresses	O
(	O
link-local	B-Protocol
address	I-Protocol
prefix	O
)	O
,	O
rendering	O
them	O
non-routable	B-Protocol
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
scope	O
field	O
is	O
used	O
to	O
identify	O
special	O
multicast	O
addresses	O
,	O
like	O
solicited	B-Protocol
node	I-Protocol
.	O
</s>
<s>
Solicited-node	O
multicast	O
addresses	O
are	O
computed	O
as	O
a	O
function	O
of	O
a	O
node	O
's	O
unicast	B-Protocol
or	O
anycast	B-Protocol
addresses	O
.	O
</s>
<s>
A	O
solicited-node	B-Protocol
multicast	I-Protocol
address	I-Protocol
is	O
created	O
by	O
copying	O
the	O
last	O
24	O
bits	O
of	O
a	O
unicast	B-Protocol
or	O
anycast	B-Protocol
address	O
to	O
the	O
last	O
24	O
bits	O
of	O
the	O
multicast	B-Protocol
address	I-Protocol
.	O
</s>
<s>
An	O
IPv6	B-Protocol
address	I-Protocol
is	O
represented	O
as	O
eight	O
groups	O
of	O
four	O
hexadecimal	O
digits	O
,	O
each	O
group	O
representing	O
16	O
bits	O
The	O
groups	O
are	O
separated	O
by	O
colons	O
(	O
:	O
)	O
.	O
</s>
<s>
An	O
example	O
of	O
an	O
IPv6	B-Protocol
address	I-Protocol
is	O
:	O
</s>
<s>
The	O
standards	O
provide	O
flexibility	O
in	O
the	O
representation	O
of	O
IPv6	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
For	O
mitigation	O
of	O
these	O
complications	O
,	O
the	O
IETF	O
has	O
defined	O
a	O
canonical	O
format	O
for	O
rendering	O
IPv6	B-Protocol
addresses	I-Protocol
in	O
text	O
:	O
</s>
<s>
These	O
methods	O
can	O
lead	O
to	O
very	O
short	O
representations	O
for	O
IPv6	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
the	O
localhost	B-Protocol
(	O
loopback	B-Protocol
)	O
address	O
,	O
,	O
and	O
the	O
IPv6	B-Protocol
unspecified	O
address	O
,	O
,	O
are	O
reduced	O
to	O
and	O
,	O
respectively	O
.	O
</s>
<s>
During	O
the	O
transition	O
of	O
the	O
Internet	O
from	O
IPv4	B-Protocol
to	O
IPv6	B-Protocol
,	O
it	O
is	O
typical	O
to	O
operate	O
in	O
a	O
mixed	O
addressing	O
environment	O
.	O
</s>
<s>
For	O
such	O
use	O
cases	O
,	O
a	O
special	O
notation	O
has	O
been	O
introduced	O
,	O
which	O
expresses	O
IPv4-mapped	O
and	O
IPv4-compatible	O
IPv6	B-Protocol
addresses	I-Protocol
by	O
writing	O
the	O
least-significant	O
32	O
bits	O
of	O
an	O
address	O
in	O
the	O
familiar	O
IPv4	B-Protocol
dot-decimal	B-Protocol
notation	I-Protocol
,	O
whereas	O
the	O
96	O
most-significant	O
bits	O
are	O
written	O
in	O
IPv6	B-Protocol
format	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
IPv4-mapped	O
IPv6	B-Protocol
address	I-Protocol
is	O
written	O
as	O
,	O
thus	O
expressing	O
clearly	O
the	O
original	O
IPv4	B-Protocol
address	O
that	O
was	O
mapped	O
to	O
IPv6	B-Protocol
.	O
</s>
<s>
An	O
IPv6	B-Protocol
network	O
uses	O
an	O
address	O
block	O
that	O
is	O
a	O
contiguous	O
group	O
of	O
IPv6	B-Protocol
addresses	I-Protocol
of	O
a	O
size	O
that	O
is	O
a	O
power	O
of	O
two	O
.	O
</s>
<s>
The	O
leading	O
set	O
of	O
bits	O
of	O
the	O
addresses	O
are	O
identical	O
for	O
all	O
hosts	O
in	O
a	O
given	O
network	O
,	O
and	O
are	O
called	O
the	O
network	O
's	O
address	O
or	O
routing	B-Protocol
prefix	O
.	O
</s>
<s>
Network	O
address	B-General_Concept
ranges	I-General_Concept
are	O
written	O
in	O
CIDR	B-Protocol
notation	I-Protocol
.	O
</s>
<s>
A	O
network	O
is	O
denoted	O
by	O
the	O
first	O
address	O
in	O
the	O
block	O
(	O
ending	O
in	O
all	O
zeroes	O
)	O
,	O
a	O
slash	O
(	O
/	O
)	O
,	O
and	O
a	O
decimal	B-Application
value	O
equal	O
to	O
the	O
size	O
in	O
bits	O
of	O
the	O
prefix	O
.	O
</s>
<s>
The	O
routing	B-Protocol
prefix	O
of	O
an	O
interface	B-Protocol
address	O
may	O
be	O
directly	O
indicated	O
with	O
the	O
address	O
using	O
CIDR	B-Protocol
notation	I-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
the	O
configuration	O
of	O
an	O
interface	B-Protocol
with	O
address	O
connected	O
to	O
subnet	O
is	O
written	O
as	O
.	O
</s>
<s>
The	O
size	O
of	O
a	O
block	O
of	O
addresses	O
is	O
specified	O
by	O
writing	O
a	O
slash	O
(	O
/	O
)	O
followed	O
by	O
a	O
number	O
in	O
decimal	B-Application
whose	O
value	O
is	O
the	O
length	O
of	O
the	O
network	O
prefix	O
in	O
bits	O
.	O
</s>
<s>
Colon	O
(	O
:	O
)	O
characters	O
in	O
IPv6	B-Protocol
addresses	I-Protocol
may	O
conflict	O
with	O
the	O
established	O
syntax	O
of	O
resource	O
identifiers	O
,	O
such	O
as	O
URIs	B-Protocol
and	O
URLs	O
.	O
</s>
<s>
The	O
colon	O
is	O
conventionally	O
used	O
to	O
terminate	O
the	O
host	O
path	O
before	O
a	O
port	B-Protocol
number	I-Protocol
.	O
</s>
<s>
To	O
alleviate	O
this	O
conflict	O
,	O
literal	O
IPv6	B-Protocol
addresses	I-Protocol
are	O
enclosed	O
in	O
square	O
brackets	O
in	O
such	O
resource	O
identifiers	O
,	O
for	O
example	O
:	O
</s>
<s>
When	O
the	O
URL	O
also	O
contains	O
a	O
port	B-Protocol
number	I-Protocol
the	O
notation	O
is	O
:	O
</s>
<s>
where	O
the	O
trailing	O
443	O
is	O
the	O
example	O
's	O
port	B-Protocol
number	I-Protocol
.	O
</s>
<s>
For	O
addresses	O
with	O
other	O
than	O
global	O
scope	O
(	O
as	O
described	O
in	O
)	O
,	O
and	O
in	O
particular	O
for	O
link-local	O
addresses	O
,	O
the	O
choice	O
of	O
the	O
network	O
interface	B-Protocol
for	O
sending	O
a	O
packet	O
may	O
depend	O
on	O
which	O
zone	O
the	O
address	O
belongs	O
to	O
.	O
</s>
<s>
Even	O
if	O
a	O
single	O
address	O
is	O
not	O
in	O
use	O
in	O
different	O
zones	O
,	O
the	O
address	O
prefixes	O
for	O
addresses	O
in	O
those	O
zones	O
may	O
still	O
be	O
identical	O
,	O
which	O
makes	O
the	O
operating	B-General_Concept
system	I-General_Concept
unable	O
to	O
select	O
an	O
outgoing	O
interface	B-Protocol
based	O
on	O
the	O
information	O
in	O
the	O
routing	B-Protocol
table	O
(	O
which	O
is	O
prefix-based	O
)	O
.	O
</s>
<s>
The	O
former	O
(	O
using	O
an	O
interface	B-Protocol
name	O
)	O
is	O
customary	O
on	O
most	O
Unix-like	O
operating	B-General_Concept
systems	I-General_Concept
(	O
e.g.	O
,	O
BSD	B-Operating_System
,	O
Linux	B-Application
,	O
macOS	B-Application
)	O
.	O
</s>
<s>
The	O
latter	O
(	O
using	O
an	O
interface	B-Protocol
number	O
)	O
is	O
the	O
standard	O
syntax	O
on	O
Microsoft	B-Application
Windows	I-Application
,	O
but	O
as	O
support	O
for	O
this	O
syntax	O
is	O
mandatory	O
,	O
it	O
is	O
also	O
available	O
on	O
other	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
BSD-based	O
operating	B-General_Concept
systems	I-General_Concept
(	O
including	O
macOS	B-Application
)	O
also	O
support	O
an	O
alternative	O
,	O
non-standard	O
syntax	O
,	O
where	O
a	O
numeric	O
zone	O
index	O
is	O
encoded	O
in	O
the	O
second	O
16-bit	O
word	O
of	O
the	O
address	O
.	O
</s>
<s>
In	O
all	O
operating	B-General_Concept
systems	I-General_Concept
mentioned	O
above	O
,	O
the	O
zone	O
index	O
for	O
link-local	O
addresses	O
actually	O
refers	O
to	O
an	O
interface	B-Protocol
,	O
not	O
to	O
a	O
zone	O
.	O
</s>
<s>
When	O
used	O
in	O
uniform	B-Protocol
resource	I-Protocol
identifiers	I-Protocol
(	O
URI	B-Protocol
)	O
,	O
the	O
use	O
of	O
the	O
percent	O
sign	O
causes	O
a	O
syntax	O
conflict	O
,	O
therefore	O
it	O
must	O
be	O
escaped	O
via	O
percent-encoding	O
,	O
e.g.	O
</s>
<s>
In	O
Microsoft	B-Application
Windows	I-Application
operating	I-Application
systems	I-Application
,	O
IPv4	B-Protocol
addresses	O
are	O
valid	O
location	O
identifiers	O
in	O
Uniform	O
Naming	O
Convention	O
(	O
UNC	O
)	O
path	O
names	O
.	O
</s>
<s>
Thus	O
,	O
the	O
use	O
of	O
IPv6	B-Protocol
addresses	I-Protocol
is	O
also	O
illegal	O
in	O
UNC	O
names	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
Microsoft	O
implemented	O
a	O
transcription	O
algorithm	O
to	O
represent	O
an	O
IPv6	B-Protocol
address	I-Protocol
in	O
the	O
form	O
of	O
a	O
domain	O
name	O
that	O
can	O
be	O
used	O
in	O
UNC	O
paths	O
.	O
</s>
<s>
For	O
this	O
purpose	O
,	O
Microsoft	O
registered	O
and	O
reserved	O
the	O
second-level	B-Protocol
domain	I-Protocol
ipv6-literal.net	O
on	O
the	O
Internet	O
(	O
although	O
they	O
gave	O
up	O
the	O
domain	O
in	O
January	O
2014	O
)	O
.	O
</s>
<s>
IPv6	B-Protocol
addresses	I-Protocol
are	O
transcribed	O
as	O
a	O
hostname	B-Protocol
or	O
subdomain	O
name	O
within	O
this	O
namespace	O
,	O
in	O
the	O
following	O
fashion	O
:	O
</s>
<s>
This	O
notation	O
is	O
automatically	O
resolved	O
locally	O
by	O
Microsoft	O
software	O
,	O
without	O
any	O
queries	O
to	O
DNS	B-Protocol
name	I-Protocol
servers	O
.	O
</s>
<s>
If	O
the	O
IPv6	B-Protocol
address	I-Protocol
contains	O
a	O
zone	O
index	O
,	O
it	O
is	O
appended	O
to	O
the	O
address	O
portion	O
after	O
an	O
'	O
s	O
 '	O
character	O
:	O
</s>
<s>
Every	O
IPv6	B-Protocol
address	I-Protocol
,	O
except	O
the	O
unspecified	O
address	O
(	O
)	O
,	O
has	O
a	O
scope	O
,	O
which	O
specifies	O
in	O
which	O
part	O
of	O
the	O
network	O
it	O
is	O
valid	O
.	O
</s>
<s>
For	O
unicast	B-Protocol
addresses	O
,	O
two	O
scopes	O
are	O
defined	O
:	O
link-local	O
and	O
global	O
.	O
</s>
<s>
Link-local	O
addresses	O
and	O
the	O
loopback	B-Protocol
address	I-Protocol
have	O
link-local	O
scope	O
,	O
which	O
means	O
they	O
can	O
only	O
be	O
used	O
on	O
a	O
single	O
directly	O
attached	O
network	O
.	O
</s>
<s>
All	O
other	O
addresses	O
(	O
including	O
Unique	O
local	O
addresses	O
)	O
have	O
global	O
(	O
or	O
universal	O
)	O
scope	O
,	O
which	O
means	O
they	O
are	O
potentially	O
globally	O
routable	B-Protocol
and	O
can	O
be	O
used	O
to	O
connect	O
to	O
addresses	O
with	O
global	O
scope	O
anywhere	O
,	O
or	O
to	O
addresses	O
with	O
link-local	O
scope	O
on	O
the	O
directly	O
attached	O
network	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
only	O
other	O
hosts	O
in	O
the	O
same	O
administrative	O
domain	O
(	O
e.g.	O
,	O
an	O
organization	O
)	O
,	O
or	O
within	O
a	O
cooperating	O
administrative	O
domain	O
are	O
able	O
to	O
reach	O
such	O
addresses	O
,	O
if	O
properly	O
routed	B-Protocol
.	O
</s>
<s>
Anycast	B-Protocol
addresses	O
are	O
syntactically	O
identical	O
to	O
and	O
indistinguishable	O
from	O
unicast	B-Protocol
addresses	O
.	O
</s>
<s>
Scopes	O
for	O
anycast	B-Protocol
addresses	O
are	O
therefore	O
the	O
same	O
as	O
for	O
unicast	B-Protocol
addresses	O
.	O
</s>
<s>
+	O
Scope	O
values	O
Value	O
Scope	O
name	O
Notes	O
0x0	O
reserved	O
0x1	O
interface-local	O
Interface-local	O
scope	O
spans	O
only	O
a	O
single	O
interface	B-Protocol
on	O
a	O
node	O
,	O
and	O
is	O
useful	O
only	O
for	O
loopback	B-Protocol
transmission	O
of	O
multicast	O
.	O
</s>
<s>
0x2	O
link-local	O
Link-local	O
scope	O
spans	O
the	O
same	O
topological	O
region	O
as	O
the	O
corresponding	O
unicast	B-Protocol
scope	O
.	O
</s>
<s>
The	O
management	O
of	O
IPv6	B-Protocol
address	I-Protocol
allocation	O
process	O
is	O
delegated	O
to	O
the	O
Internet	O
Assigned	O
Numbers	O
Authority	O
(	O
IANA	O
)	O
by	O
the	O
Internet	O
Architecture	O
Board	O
and	O
the	O
Internet	O
Engineering	O
Steering	O
Group	O
.	O
</s>
<s>
The	O
IANA	O
has	O
maintained	O
the	O
official	O
list	O
of	O
allocations	O
of	O
the	O
IPv6	B-Protocol
address	I-Protocol
space	I-Protocol
since	O
December	O
1995	O
.	O
</s>
<s>
In	O
order	O
to	O
allow	O
efficient	O
route	B-Protocol
aggregation	I-Protocol
,	O
thereby	O
reducing	O
the	O
size	O
of	O
the	O
Internet	O
routing	B-Protocol
tables	O
,	O
only	O
one-eighth	O
of	O
the	O
total	O
address	B-General_Concept
space	I-General_Concept
(	O
)	O
is	O
currently	O
allocated	O
for	O
use	O
on	O
the	O
Internet	O
.	O
</s>
<s>
The	O
rest	O
of	O
the	O
IPv6	B-Protocol
address	I-Protocol
space	I-Protocol
is	O
reserved	O
for	O
future	O
use	O
or	O
for	O
special	O
purposes	O
.	O
</s>
<s>
The	O
address	B-General_Concept
space	I-General_Concept
is	O
assigned	O
to	O
the	O
RIRs	O
in	O
blocks	O
of	O
up	O
to	O
.	O
</s>
<s>
Global	O
unicast	B-Protocol
assignment	O
records	O
can	O
be	O
found	O
at	O
the	O
various	O
RIRs	O
or	O
other	O
websites	O
.	O
</s>
<s>
IPv6	B-Protocol
addresses	I-Protocol
are	O
assigned	O
to	O
organizations	O
in	O
much	O
larger	O
blocks	O
as	O
compared	O
to	O
IPv4	B-Protocol
address	O
assignments	O
—	O
the	O
recommended	O
allocation	O
is	O
a	O
block	O
which	O
contains	O
280	O
addresses	O
,	O
being	O
248	O
or	O
about	O
times	O
larger	O
than	O
the	O
entire	O
IPv4	B-Protocol
address	B-General_Concept
space	I-General_Concept
of	O
232	O
addresses	O
and	O
about	O
times	O
larger	O
than	O
the	O
blocks	O
of	O
IPv4	B-Protocol
addresses	O
,	O
which	O
are	O
the	O
largest	O
allocations	O
of	O
IPv4	B-Protocol
addresses	O
.	O
</s>
<s>
The	O
total	O
pool	O
,	O
however	O
,	O
is	O
sufficient	O
for	O
the	O
foreseeable	O
future	O
,	O
because	O
there	O
are	O
2128	O
(	O
exactly	O
340,282,366,920,938,463,463,374,607,431,768,211,456	O
)	O
or	O
about	O
(	O
340	O
trillion	O
trillion	O
trillion	O
)	O
unique	O
IPv6	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
In	O
contrast	O
,	O
the	O
entire	O
IPv4	B-Protocol
address	B-General_Concept
space	I-General_Concept
has	O
only	O
232	O
(	O
exactly	O
4,294,967,296	O
or	O
about	O
)	O
addresses	O
.	O
</s>
<s>
By	O
design	O
,	O
only	O
a	O
very	O
small	O
fraction	O
of	O
the	O
address	B-General_Concept
space	I-General_Concept
will	O
actually	O
be	O
used	O
.	O
</s>
<s>
The	O
large	O
address	B-General_Concept
space	I-General_Concept
ensures	O
that	O
addresses	O
are	O
almost	O
always	O
available	O
,	O
which	O
makes	O
the	O
use	O
of	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
NAT	O
)	O
for	O
the	O
purposes	O
of	O
address	O
conservation	O
completely	O
unnecessary	O
.	O
</s>
<s>
NAT	O
has	O
been	O
increasingly	O
used	O
for	O
IPv4	B-Protocol
networks	I-Protocol
to	O
help	O
alleviate	O
IPv4	B-Protocol
address	I-Protocol
exhaustion	I-Protocol
.	O
</s>
<s>
Provider-independent	B-Protocol
address	I-Protocol
space	I-Protocol
is	O
assigned	O
directly	O
to	O
the	O
end	O
user	O
by	O
the	O
RIRs	O
from	O
the	O
special	O
range	O
and	O
allows	O
customers	O
to	O
make	O
provider	O
changes	O
without	O
renumbering	O
their	O
networks	O
.	O
</s>
<s>
Internet	B-Protocol
Exchange	I-Protocol
Points	I-Protocol
(	O
IXPs	B-Protocol
)	O
are	O
assigned	O
special	O
addresses	O
from	O
the	O
ranges	O
,	O
,	O
and	O
for	O
communication	O
with	O
their	O
connected	O
ISPs	O
.	O
</s>
<s>
Root	B-Application
name	I-Application
servers	I-Application
have	O
been	O
assigned	O
addresses	O
from	O
the	O
range	O
.	O
</s>
<s>
The	O
lowest	O
address	O
within	O
each	O
subnet	O
prefix	O
(	O
the	O
interface	B-Protocol
identifier	O
set	O
to	O
all	O
zeroes	O
)	O
is	O
reserved	O
as	O
the	O
subnet-router	O
anycast	B-Protocol
address	O
.	O
</s>
<s>
Applications	O
may	O
use	O
this	O
address	O
when	O
talking	O
to	O
any	O
one	O
of	O
the	O
available	O
routers	B-Protocol
,	O
as	O
packets	O
sent	O
to	O
this	O
address	O
are	O
delivered	O
to	O
just	O
one	O
router	B-Protocol
.	O
</s>
<s>
The	O
128	O
highest	O
addresses	O
within	O
each	O
subnet	O
prefix	O
are	O
reserved	O
to	O
be	O
used	O
as	O
anycast	B-Protocol
addresses	O
.	O
</s>
<s>
These	O
addresses	O
usually	O
have	O
the	O
first	O
57	O
bits	O
of	O
the	O
interface	B-Protocol
identifier	O
set	O
to	O
1	O
,	O
followed	O
by	O
the	O
7-bit	O
anycast	B-Protocol
ID	O
.	O
</s>
<s>
Prefixes	O
for	O
the	O
network	O
can	O
be	O
of	O
any	O
length	O
for	O
routing	B-Protocol
purposes	O
,	O
but	O
subnets	O
are	O
required	O
to	O
have	O
a	O
length	O
of	O
64	O
bits	O
.	O
</s>
<s>
The	O
address	O
with	O
value	O
0x7e	O
in	O
the	O
7	O
least-significant	O
bits	O
is	O
defined	O
as	O
a	O
mobile	B-Protocol
IPv6	I-Protocol
home	O
agents	O
anycast	B-Protocol
address	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
addresses	O
with	O
special	O
meaning	O
in	O
IPv6	B-Protocol
.	O
</s>
<s>
They	O
represent	O
less	O
than	O
2%	O
of	O
the	O
entire	O
address	B-General_Concept
space	I-General_Concept
:	O
</s>
<s>
—	O
The	O
default	B-Protocol
route	I-Protocol
address	O
(	O
corresponding	O
to	O
in	O
IPv4	B-Protocol
)	O
for	O
destination	O
addresses	O
(	O
unicast	B-Protocol
,	O
multicast	O
and	O
others	O
)	O
not	O
specified	O
elsewhere	O
in	O
a	O
routing	B-Protocol
table	O
.	O
</s>
<s>
—	O
The	O
address	O
with	O
all	O
zero	O
bits	O
is	O
called	O
the	O
unspecified	O
address	O
(	O
corresponding	O
to	O
in	O
IPv4	B-Protocol
)	O
.This	O
address	O
must	O
never	O
be	O
assigned	O
to	O
an	O
interface	B-Protocol
and	O
is	O
to	O
be	O
used	O
only	O
in	O
software	O
before	O
the	O
application	O
has	O
learned	O
its	O
host	O
's	O
source	O
address	O
appropriate	O
for	O
a	O
pending	O
connection	O
.	O
</s>
<s>
Routers	B-Protocol
must	O
not	O
forward	O
packets	O
with	O
the	O
unspecified	O
address.Applications	O
may	O
be	O
listening	O
on	O
one	O
or	O
more	O
specific	O
interfaces	O
for	O
incoming	O
connections	O
,	O
which	O
are	O
shown	O
in	O
listings	O
of	O
active	O
internet	O
connections	O
by	O
a	O
specific	O
IP	B-Protocol
address	I-Protocol
(	O
and	O
a	O
port	B-Protocol
number	I-Protocol
,	O
separated	O
by	O
a	O
colon	O
)	O
.	O
</s>
<s>
—	O
The	O
loopback	B-Protocol
address	I-Protocol
is	O
a	O
unicast	B-Protocol
localhost	B-Protocol
address	O
(	O
corresponding	O
to	O
in	O
IPv4	B-Protocol
)	O
.If	O
an	O
application	O
in	O
a	O
host	O
sends	O
packets	O
to	O
this	O
address	O
,	O
the	O
IPv6	B-Protocol
stack	O
will	O
loop	O
these	O
packets	O
back	O
on	O
the	O
same	O
virtual	O
interface	B-Protocol
.	O
</s>
<s>
—	O
Addresses	O
in	O
the	O
link-local	O
prefix	O
are	O
only	O
valid	O
and	O
unique	O
on	O
a	O
single	O
link	O
(	O
comparable	O
to	O
the	O
auto-configuration	O
addresses	O
of	O
IPv4	B-Protocol
)	O
.Within	O
this	O
prefix	O
only	O
one	O
subnet	O
is	O
allocated	O
(	O
54	O
zero	O
bits	O
)	O
,	O
yielding	O
an	O
effective	O
format	O
of	O
.	O
</s>
<s>
The	O
least	O
significant	O
64	O
bits	O
were	O
previously	O
chosen	O
as	O
the	O
interface	B-Protocol
hardware	O
address	O
constructed	O
in	O
modified	O
EUI-64	O
format	O
,	O
but	O
are	O
now	O
pseudo-random	B-Error_Name
values	O
for	O
privacy	O
.	O
</s>
<s>
A	O
link-local	B-Protocol
address	I-Protocol
is	O
required	O
on	O
every	O
IPv6-enabled	O
interface	B-Protocol
—	O
in	O
other	O
words	O
,	O
applications	O
may	O
rely	O
on	O
the	O
existence	O
of	O
a	O
link-local	B-Protocol
address	I-Protocol
even	O
when	O
there	O
is	O
no	O
IPv6	B-Protocol
routing	B-Protocol
.	O
</s>
<s>
—	O
Unique	O
local	O
addresses	O
(	O
ULAs	O
)	O
are	O
intended	O
for	O
local	O
communication	O
(	O
comparable	O
to	O
IPv4	B-Protocol
private	I-Protocol
addresses	I-Protocol
,	O
and	O
)	O
.They	O
are	O
routable	B-Protocol
only	O
within	O
a	O
set	O
of	O
cooperating	O
sites	O
.	O
</s>
<s>
The	O
upper	O
half	O
(	O
)	O
is	O
used	O
for	O
"	O
probabilistically	O
unique	O
"	O
addresses	O
in	O
which	O
the	O
prefix	O
is	O
combined	O
with	O
a	O
40-bit	O
locally	O
generated	O
pseudorandom	B-Error_Name
number	I-Error_Name
to	O
obtain	O
a	O
private	O
prefix	O
.	O
</s>
<s>
—	O
This	O
prefix	O
is	O
used	O
for	O
IPv6	B-Protocol
transition	I-Protocol
mechanisms	I-Protocol
and	O
designated	O
as	O
an	O
IPv4-mapped	O
IPv6	B-Protocol
address.With	O
a	O
few	O
exceptions	O
,	O
this	O
address	O
type	O
allows	O
the	O
transparent	O
use	O
of	O
the	O
transport	B-Architecture
layer	I-Architecture
protocols	O
over	O
IPv4	B-Protocol
through	O
the	O
IPv6	B-Protocol
networking	O
application	B-Application
programming	I-Application
interface	I-Application
.	O
</s>
<s>
Server	O
applications	O
only	O
need	O
to	O
open	O
a	O
single	O
listening	O
socket	B-Protocol
to	O
handle	O
connections	O
from	O
clients	O
using	O
IPv6	B-Protocol
or	O
IPv4	B-Protocol
protocols	O
.	O
</s>
<s>
IPv6	B-Protocol
clients	O
will	O
be	O
handled	O
natively	O
by	O
default	O
,	O
and	O
IPv4	B-Protocol
clients	O
appear	O
as	O
IPv6	B-Protocol
clients	O
at	O
their	O
IPv4-mapped	O
IPv6	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Transmission	O
is	O
handled	O
similarly	O
;	O
established	O
sockets	O
may	O
be	O
used	O
to	O
transmit	O
IPv4	B-Protocol
or	O
IPv6	B-Protocol
datagram	O
,	O
based	O
on	O
the	O
binding	O
to	O
an	O
IPv6	B-Protocol
address	I-Protocol
,	O
or	O
an	O
IPv4-mapped	O
address	O
.	O
</s>
<s>
—	O
A	O
prefix	O
used	O
for	O
IPv4-translated	O
addresses.These	O
are	O
used	O
by	O
the	O
Stateless	O
IP/ICMP	O
Translation	O
(	O
SIIT	O
)	O
protocol	O
.	O
</s>
<s>
—	O
The	O
"	O
Well-Known	O
"	O
Prefix.Addresses	O
with	O
this	O
prefix	O
are	O
used	O
for	O
automatic	O
IPv4/IPv6	O
translation	O
.	O
</s>
<s>
—	O
A	O
prefix	O
for	O
locally	O
translated	O
IPv4/IPv6	O
addresses.Addresses	O
with	O
this	O
prefix	O
can	O
be	O
used	O
for	O
multiple	O
IPv4/IPv6	O
translation	O
mechanisms	O
like	O
NAT64	B-Protocol
and	O
SIIT.It	O
is	O
defined	O
in	O
RFC8215	O
and	O
compared	O
to	O
64:ff9b::/96	O
it	O
contains	O
the	O
IPv4	B-Protocol
address	O
in	O
position	O
48-63	O
and	O
72-87	O
(	O
see	O
RFC6052	O
)	O
.	O
</s>
<s>
This	O
means	O
that	O
for	O
every	O
IPv4	B-Protocol
address	O
a	O
/80	O
IPv6	B-Protocol
prefix	O
is	O
assigned	O
to	O
the	O
device	O
.	O
</s>
<s>
This	O
enables	O
similar	O
use	O
cases	O
as	O
6to4	B-Protocol
,	O
where	O
a	O
single	O
public	O
IPv4	B-Protocol
address	O
gets	O
translated	O
into	O
a	O
prefix	O
.	O
</s>
<s>
—	O
This	O
prefix	O
was	O
used	O
for	O
6to4	B-Protocol
addressing	O
(	O
an	O
address	O
from	O
the	O
IPv4	B-Protocol
network	I-Protocol
was	O
also	O
used	O
)	O
.The	O
6to4	B-Protocol
addressing	O
scheme	O
is	O
deprecated	O
.	O
</s>
<s>
—	O
Used	O
for	O
Teredo	B-Protocol
tunneling	I-Protocol
.	O
</s>
<s>
—	O
Used	O
for	O
benchmarking	O
IPv6	B-Protocol
(	O
corresponding	O
to	O
for	O
benchmarking	O
IPv4	B-Protocol
)	O
.Assigned	O
to	O
the	O
Benchmarking	O
Methodology	O
Working	O
Group	O
(	O
BMWG	O
)	O
.	O
</s>
<s>
—	O
ORCHIDv2	O
(	O
Overlay	O
Routable	B-Protocol
Cryptographic	O
Hash	B-Error_Name
Identifiers	O
)	O
.These	O
are	O
non-routed	O
IPv6	B-Protocol
addresses	I-Protocol
used	O
for	O
Cryptographic	O
Hash	B-Error_Name
Identifiers	O
.	O
</s>
<s>
—	O
This	O
prefix	O
is	O
used	O
in	O
documentation	O
(	O
corresponding	O
to	O
,	O
,	O
and	O
in	O
IPv4	B-Protocol
.	O
</s>
<s>
)	O
The	O
addresses	O
should	O
be	O
used	O
anywhere	O
an	O
example	O
IPv6	B-Protocol
address	I-Protocol
is	O
given	O
or	O
model	O
networking	O
scenarios	O
are	O
described	O
.	O
</s>
<s>
Some	O
common	O
IPv6	B-Protocol
multicast	O
addresses	O
are	O
the	O
following	O
:	O
</s>
<s>
Address	O
Description	O
Available	O
Scopes	O
ff0X::1	O
All	O
nodes	O
address	O
,	O
identify	O
the	O
group	O
of	O
all	O
IPv6	B-Protocol
nodes	O
Available	O
in	O
scope	O
1	O
(	O
interface-local	O
)	O
and	O
2	O
(	O
link-local	O
)	O
:	O
</s>
<s>
ff02::1	O
→	O
All	O
nodes	O
in	O
the	O
link-local	O
ff0X::2	O
All	O
routers	B-Protocol
Available	O
in	O
scope	O
1	O
(	O
interface-local	O
)	O
,	O
2	O
(	O
link-local	O
)	O
and	O
5	O
(	O
site-local	O
)	O
:	O
</s>
<s>
ff05::2	O
→	O
All	O
routers	B-Protocol
in	O
the	O
site-local	O
ff02::5	O
OSPFIGP	B-Protocol
2	O
(	O
link-local	O
)	O
ff02::6	O
OSPFIGP	B-Protocol
designated	O
routers	B-Protocol
2	O
(	O
link-local	O
)	O
ff02::9	O
RIP	B-Protocol
routers	B-Protocol
2	O
(	O
link-local	O
)	O
ff02::a	O
EIGRP	B-Protocol
routers	B-Protocol
2	O
(	O
link-local	O
)	O
ff02::d	O
All	O
PIM	B-Protocol
routers	B-Protocol
2	O
(	O
link-local	O
)	O
ff02::1a	O
All	O
RPL	B-Protocol
routers	B-Protocol
2	O
(	O
link-local	O
)	O
ff0X::fb	O
mDNSv6	B-Protocol
Available	O
in	O
all	O
scopes	O
ff0X::101	O
All	O
NTP	B-Protocol
servers	I-Protocol
Available	O
in	O
all	O
scopes	O
ff02::1:1	O
Link	O
name	O
2	O
(	O
link-local	O
)	O
ff02::1:2	O
All-dhcp-agents	O
(	O
DHCPv6	B-Protocol
)	O
2	O
(	O
link-local	O
)	O
ff02::1:3	O
Link-local	O
multicast	O
name	O
resolution	O
2	O
(	O
link-local	O
)	O
ff05::1:3	O
All-dhcp-servers	O
(	O
DHCPv6	B-Protocol
)	O
5	O
(	O
site-local	O
)	O
ff02::1:ff00:0/104	O
Solicited-node	B-Protocol
multicast	I-Protocol
address	I-Protocol
.	O
</s>
<s>
The	O
least	O
significant	O
24	O
bits	O
of	O
the	O
solicited-node	B-Protocol
multicast	I-Protocol
address	I-Protocol
group	O
ID	O
are	O
filled	O
with	O
the	O
least	O
significant	O
24	O
bits	O
of	O
the	O
interface	B-Protocol
's	O
unicast	B-Protocol
or	O
anycast	B-Protocol
address	O
.	O
</s>
<s>
These	O
addresses	O
allow	O
link	O
layer	O
address	O
resolution	O
via	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
(	O
NDP	O
)	O
on	O
the	O
link	O
without	O
disturbing	O
all	O
nodes	O
on	O
the	O
local	O
network	O
.	O
</s>
<s>
A	O
host	O
is	O
required	O
to	O
join	O
a	O
solicited-node	O
multicast	O
group	O
for	O
each	O
of	O
its	O
configured	O
unicast	B-Protocol
or	O
anycast	B-Protocol
addresses	O
.	O
</s>
<s>
On	O
system	O
startup	O
,	O
a	O
node	O
automatically	O
creates	O
a	O
link-local	B-Protocol
address	I-Protocol
on	O
each	O
IPv6-enabled	O
interface	B-Protocol
,	O
even	O
if	O
globally	O
routable	B-Protocol
addresses	O
are	O
manually	O
configured	O
or	O
obtained	O
through	O
"	O
configuration	O
protocols	O
"	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
It	O
does	O
so	O
independently	O
and	O
without	O
any	O
prior	O
configuration	O
by	O
stateless	B-Protocol
address	I-Protocol
autoconfiguration	I-Protocol
(	O
SLAAC	O
)	O
,	O
using	O
a	O
component	O
of	O
the	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
In	O
IPv4	B-Protocol
,	O
typical	O
"	O
configuration	O
protocols	O
"	O
include	O
DHCP	O
or	O
PPP	O
.	O
</s>
<s>
Although	O
DHCPv6	B-Protocol
exists	O
,	O
IPv6	B-Protocol
hosts	O
normally	O
use	O
the	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
to	O
create	O
a	O
globally	O
routable	B-Protocol
unicast	B-Protocol
address	I-Protocol
:	O
the	O
host	O
sends	O
router	B-Protocol
solicitation	O
requests	O
and	O
an	O
IPv6	B-Protocol
router	B-Protocol
responds	O
with	O
a	O
prefix	O
assignment	O
.	O
</s>
<s>
The	O
lower	O
64	O
bits	O
of	O
these	O
addresses	O
are	O
populated	O
with	O
a	O
64-bit	O
interface	B-Protocol
identifier	O
.	O
</s>
<s>
This	O
should	O
be	O
a	O
pseudo-random	B-Error_Name
number	I-Error_Name
for	O
privacy	O
reasons	O
.	O
</s>
<s>
Also	O
for	O
privacy	O
reasons	O
,	O
the	O
interface	B-Protocol
identifier	O
is	O
different	O
for	O
each	O
automatically	O
configured	O
address	O
of	O
that	O
interface	B-Protocol
.	O
</s>
<s>
This	O
has	O
the	O
disadvantage	O
that	O
multiple	O
multicast	O
groups	O
need	O
to	O
be	O
joined	O
for	O
neighbor	B-Protocol
discovery	I-Protocol
.	O
</s>
<s>
For	O
this	O
,	O
a	O
multicast	B-Protocol
address	I-Protocol
is	O
used	O
,	O
formed	O
from	O
the	O
network	O
prefix	O
and	O
the	O
24	O
least	O
significant	O
bits	O
of	O
the	O
address	O
.	O
</s>
<s>
A	O
64-bit	O
interface	B-Protocol
identifier	O
was	O
previously	O
derived	O
from	O
the	O
interface	B-Protocol
's	O
48-bit	O
MAC	O
address	O
,	O
although	O
this	O
method	O
is	O
now	O
deprecated	O
.	O
</s>
<s>
When	O
this	O
EUI-64	O
is	O
used	O
to	O
form	O
an	O
IPv6	B-Protocol
address	I-Protocol
,	O
it	O
is	O
modified	O
:	O
the	O
meaning	O
of	O
the	O
Universal/Local	O
bit	O
(	O
the	O
7th	O
most	O
significant	O
bit	O
of	O
the	O
EUI-64	O
,	O
starting	O
from	O
1	O
)	O
is	O
inverted	O
,	O
so	O
that	O
a	O
1	O
now	O
means	O
Universal	O
.	O
</s>
<s>
To	O
create	O
an	O
IPv6	B-Protocol
address	I-Protocol
with	O
the	O
network	O
prefix	O
it	O
yields	O
the	O
address	O
(	O
with	O
the	O
Universal/Local	O
bit	O
,	O
the	O
second-least-significant	O
bit	O
of	O
the	O
underlined	O
quartet	O
,	O
inverted	O
to	O
1	O
in	O
this	O
case	O
because	O
the	O
MAC	O
address	O
is	O
universally	O
unique	O
)	O
.	O
</s>
<s>
The	O
assignment	O
of	O
a	O
unicast	B-Protocol
IPv6	B-Protocol
address	I-Protocol
to	O
an	O
interface	B-Protocol
involves	O
an	O
internal	O
test	O
for	O
the	O
uniqueness	O
of	O
that	O
address	O
using	O
Neighbor	O
Solicitation	O
and	O
Neighbor	O
Advertisement	O
(	O
ICMPv6	B-Protocol
type	O
135	O
and	O
136	O
)	O
messages	O
.	O
</s>
<s>
The	O
node	O
joins	O
the	O
solicited-node	B-Protocol
multicast	I-Protocol
address	I-Protocol
for	O
the	O
tentative	O
address	O
(	O
if	O
not	O
already	O
done	O
so	O
)	O
and	O
sends	O
neighbor	O
solicitations	O
,	O
with	O
the	O
tentative	O
address	O
as	O
target	O
address	O
and	O
the	O
unspecified	O
address	O
(	O
)	O
as	O
source	O
address	O
.	O
</s>
<s>
The	O
node	O
also	O
joins	O
the	O
all-hosts	O
multicast	B-Protocol
address	I-Protocol
,	O
so	O
it	O
will	O
be	O
able	O
to	O
receive	O
Neighbor	O
Advertisements	O
.	O
</s>
<s>
Only	O
after	O
having	O
successfully	O
established	O
that	O
an	O
address	O
is	O
unique	O
may	O
it	O
be	O
assigned	O
and	O
used	O
by	O
an	O
interface	B-Protocol
.	O
</s>
<s>
When	O
an	O
anycast	B-Protocol
address	O
is	O
assigned	O
to	O
an	O
interface	B-Protocol
,	O
like	O
a	O
subnet-router	O
anycast	B-Protocol
address	O
,	O
duplicate	O
address	O
detection	O
is	O
not	O
performed	O
.	O
</s>
<s>
Each	O
IPv6	B-Protocol
address	I-Protocol
that	O
is	O
bound	O
to	O
an	O
interface	B-Protocol
has	O
a	O
fixed	O
lifetime	O
.	O
</s>
<s>
Lifetimes	O
can	O
be	O
configured	O
in	O
routers	B-Protocol
that	O
provide	O
the	O
values	O
used	O
for	O
autoconfiguration	O
,	O
or	O
specified	O
when	O
manually	O
configuring	O
addresses	O
on	O
interfaces	O
.	O
</s>
<s>
When	O
an	O
address	O
is	O
assigned	O
to	O
an	O
interface	B-Protocol
it	O
gets	O
the	O
status	O
"	O
preferred	O
"	O
,	O
which	O
it	O
holds	O
during	O
its	O
preferred-lifetime	O
.	O
</s>
<s>
The	O
address	O
becomes	O
"	O
invalid	O
"	O
after	O
its	O
valid-lifetime	O
also	O
expires	O
;	O
the	O
address	O
is	O
removed	O
from	O
the	O
interface	B-Protocol
and	O
may	O
be	O
assigned	O
somewhere	O
else	O
on	O
the	O
Internet	O
.	O
</s>
<s>
Note	O
:	O
In	O
most	O
cases	O
,	O
the	O
lifetime	O
does	O
not	O
expire	O
because	O
new	O
Router	B-Protocol
Advertisements	O
(	O
RAs	O
)	O
refresh	O
the	O
timers	O
.	O
</s>
<s>
The	O
globally	O
unique	O
and	O
static	O
MAC	O
addresses	O
,	O
used	O
by	O
stateless	B-Protocol
address	I-Protocol
autoconfiguration	I-Protocol
to	O
create	O
interface	B-Protocol
identifiers	O
,	O
offer	O
an	O
opportunity	O
to	O
track	O
user	O
equipment	O
—	O
across	O
time	O
and	O
IPv6	B-Protocol
network	O
prefix	O
changes	O
—	O
and	O
so	O
users	O
.	O
</s>
<s>
To	O
reduce	O
the	O
prospect	O
of	O
a	O
user	O
identity	O
being	O
permanently	O
tied	O
to	O
an	O
IPv6	B-Protocol
address	I-Protocol
portion	O
,	O
a	O
node	O
may	O
create	O
temporary	O
addresses	O
with	O
interface	B-Protocol
identifiers	O
based	O
on	O
time-varying	O
random	O
bit	O
strings	O
and	O
relatively	O
short	O
lifetimes	O
(	O
hours	O
to	O
days	O
)	O
,	O
after	O
which	O
they	O
are	O
replaced	O
with	O
new	O
addresses	O
.	O
</s>
<s>
Temporary	O
addresses	O
may	O
be	O
used	O
as	O
source	O
address	O
for	O
originating	O
connections	O
,	O
while	O
external	O
hosts	O
use	O
a	O
public	O
address	O
by	O
querying	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
.	O
</s>
<s>
Network	O
interfaces	O
configured	O
for	O
IPv6	B-Protocol
use	O
temporary	O
addresses	O
by	O
default	O
in	O
OS	B-Application
X	I-Application
Lion	I-Application
and	O
later	O
Apple	O
systems	O
as	O
well	O
as	O
in	O
Windows	B-Application
Vista	I-Application
,	O
Windows	B-Device
2008	I-Device
Server	I-Device
and	O
later	O
Microsoft	O
systems	O
.	O
</s>
<s>
As	O
a	O
means	O
to	O
enhance	O
security	O
for	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
cryptographically	O
generated	O
addresses	O
(	O
or	O
CGAs	O
)	O
were	O
introduced	O
in	O
2005	O
as	O
part	O
of	O
the	O
Secure	B-Protocol
Neighbor	I-Protocol
Discovery	I-Protocol
(	O
SEND	O
)	O
Protocol	O
.	O
</s>
<s>
Such	O
an	O
address	O
is	O
generated	O
using	O
two	O
hash	B-Error_Name
functions	I-Error_Name
that	O
take	O
several	O
inputs	O
.	O
</s>
<s>
The	O
first	O
uses	O
a	O
public	O
key	O
and	O
a	O
random	O
modifier	O
;	O
the	O
latter	O
being	O
incremented	O
repeatedly	O
until	O
a	O
specific	O
amount	O
of	O
zero	O
bits	O
of	O
the	O
resulting	O
hash	B-Error_Name
is	O
acquired	O
.	O
</s>
<s>
(	O
Comparable	O
with	O
the	O
'	O
proof	O
of	O
work	O
 '	O
field	O
in	O
Bitcoin	B-Protocol
mining	O
.	O
)	O
</s>
<s>
The	O
second	O
hash	B-Error_Name
function	I-Error_Name
takes	O
the	O
network	O
prefix	O
and	O
the	O
previous	O
hash	B-Error_Name
value	I-Error_Name
.	O
</s>
<s>
The	O
least	O
significant	O
64	O
bits	O
of	O
the	O
second	O
hash	B-Error_Name
result	O
is	O
appended	O
to	O
the	O
64-bit	O
network	O
prefix	O
to	O
form	O
a	O
128-bit	O
address	O
.	O
</s>
<s>
The	O
hash	B-Error_Name
functions	I-Error_Name
can	O
also	O
be	O
used	O
to	O
verify	O
if	O
a	O
specific	O
IPv6	B-Protocol
address	I-Protocol
satisfies	O
the	O
requirement	O
of	O
being	O
a	O
valid	O
CGA	O
.	O
</s>
<s>
It	O
also	O
permits	O
vendor-specific	O
attack	O
strategies	O
,	O
and	O
reduces	O
the	O
size	O
of	O
the	O
address	B-General_Concept
space	I-General_Concept
for	O
searching	O
for	O
attack	O
targets	O
.	O
</s>
<s>
They	O
are	O
chosen	O
deterministically	O
,	O
but	O
randomly	O
,	O
in	O
the	O
entire	O
address	B-General_Concept
space	I-General_Concept
of	O
the	O
network	O
.	O
</s>
<s>
Generation	O
of	O
a	O
stable	O
privacy	O
address	O
is	O
based	O
on	O
a	O
hash	B-Error_Name
function	I-Error_Name
that	O
uses	O
several	O
stable	O
parameters	O
.	O
</s>
<s>
It	O
is	O
implementation	O
specific	O
,	O
but	O
it	O
is	O
recommended	O
to	O
use	O
at	O
least	O
the	O
network	O
prefix	O
,	O
the	O
name	O
of	O
the	O
network	O
interface	B-Protocol
,	O
a	O
duplicate	O
address	O
counter	O
,	O
and	O
a	O
secret	O
key	O
.	O
</s>
<s>
The	O
resulting	O
hash	B-Error_Name
value	I-Error_Name
is	O
used	O
to	O
construct	O
the	O
final	O
address	O
:	O
Typically	O
the	O
64	O
least	O
significant	O
bits	O
are	O
concatenated	O
to	O
the	O
64-bit	O
network	O
prefix	O
,	O
to	O
yield	O
a	O
128-bit	O
address	O
.	O
</s>
<s>
If	O
the	O
network	O
prefix	O
is	O
smaller	O
than	O
64	O
bits	O
,	O
more	O
bits	O
of	O
the	O
hash	B-Error_Name
are	O
used	O
.	O
</s>
<s>
If	O
the	O
resulting	O
address	O
does	O
not	O
conflict	O
with	O
existing	O
or	O
reserved	O
addresses	O
,	O
it	O
is	O
assigned	O
to	O
the	O
interface	B-Protocol
.	O
</s>
<s>
IPv6-enabled	O
network	O
interfaces	O
usually	O
have	O
more	O
than	O
one	O
IPv6	B-Protocol
address	I-Protocol
,	O
for	O
example	O
,	O
a	O
link-local	O
and	O
a	O
global	O
address	O
.	O
</s>
<s>
IPv6	B-Protocol
introduces	O
the	O
concepts	O
of	O
address	O
scope	O
and	O
selection	O
preference	O
,	O
yielding	O
multiple	O
choices	O
for	O
source	O
and	O
destination	O
address	O
selections	O
in	O
communication	O
with	O
another	O
host	O
.	O
</s>
<s>
The	O
preference	O
selection	O
algorithm	O
selects	O
the	O
most	O
appropriate	O
address	O
to	O
use	O
in	O
communications	O
with	O
a	O
particular	O
destination	O
,	O
including	O
the	O
use	O
of	O
IPv4-mapped	O
addresses	O
in	O
dual-stack	O
implementations	O
.	O
</s>
<s>
It	O
uses	O
a	O
configurable	O
preference	O
table	O
that	O
associates	O
each	O
routing	B-Protocol
prefix	O
with	O
a	O
precedence	O
level	O
.	O
</s>
<s>
The	O
default	O
configuration	O
places	O
preference	O
on	O
IPv6	B-Protocol
usage	O
,	O
and	O
selects	O
destination	O
addresses	O
within	O
the	O
smallest	O
possible	O
scope	O
,	O
so	O
that	O
link-local	O
communication	O
is	O
preferred	O
over	O
globally	O
routed	B-Protocol
paths	O
when	O
otherwise	O
equally	O
suitable	O
.	O
</s>
<s>
The	O
prefix	O
policy	O
table	O
is	O
similar	O
to	O
a	O
routing	B-Protocol
table	O
,	O
with	O
the	O
precedence	O
value	O
serving	O
as	O
the	O
role	O
of	O
a	O
link	O
cost	O
,	O
where	O
higher	O
preference	O
is	O
expressed	O
as	O
a	O
larger	O
value	O
.	O
</s>
<s>
Candidate	O
source	O
addresses	O
are	O
obtained	O
from	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
candidate	O
destination	O
addresses	O
may	O
be	O
queried	O
via	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
.	O
</s>
<s>
For	O
minimizing	O
the	O
time	O
of	O
establishing	O
connections	O
when	O
multiple	O
addresses	O
are	O
available	O
for	O
communication	O
,	O
the	O
Happy	B-Protocol
Eyeballs	I-Protocol
algorithm	O
was	O
devised	O
.	O
</s>
<s>
It	O
queries	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
for	O
IPv6	B-Protocol
and	O
IPv4	B-Protocol
addresses	O
of	O
the	O
target	O
host	O
,	O
sorts	O
candidate	O
addresses	O
using	O
the	O
default	O
address	O
selection	O
table	O
,	O
and	O
tries	O
to	O
establish	O
connections	O
in	O
parallel	O
.	O
</s>
<s>
In	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
,	O
hostnames	B-Protocol
are	O
mapped	O
to	O
IPv6	B-Protocol
addresses	I-Protocol
by	O
AAAA	O
resource	O
records	O
,	O
so-called	O
quad-A	O
records	O
.	O
</s>
<s>
For	O
reverse	B-Protocol
lookup	I-Protocol
the	O
IETF	O
reserved	O
the	O
domain	O
ip6.arpa	O
,	O
where	O
the	O
name	O
space	O
is	O
hierarchically	O
divided	O
by	O
the	O
1-digit	O
hexadecimal	O
representation	O
of	O
nibble	O
units	O
(	O
4	O
bits	O
)	O
of	O
the	O
IPv6	B-Protocol
address	I-Protocol
.	O
</s>
<s>
As	O
in	O
IPv4	B-Protocol
,	O
each	O
host	O
is	O
represented	O
in	O
the	O
DNS	B-Protocol
by	O
two	O
DNS	B-Protocol
records	O
:	O
an	O
address	O
record	O
and	O
a	O
reverse	O
mapping	O
pointer	O
record	O
.	O
</s>
<s>
a	O
host	O
computer	O
named	O
derrick	O
in	O
zone	O
example.com	O
has	O
the	O
Unique	B-Protocol
Local	I-Protocol
Address	I-Protocol
.	O
</s>
<s>
The	O
DNS	B-Protocol
protocol	I-Protocol
is	O
independent	O
of	O
its	O
transport	B-Architecture
layer	I-Architecture
protocol	O
.	O
</s>
<s>
Queries	O
and	O
replies	O
may	O
be	O
transmitted	O
over	O
IPv6	B-Protocol
or	O
IPv4	B-Protocol
transports	O
regardless	O
of	O
the	O
address	O
family	O
of	O
the	O
data	O
requested	O
.	O
</s>
<s>
It	O
was	O
part	O
of	O
the	O
original	O
addressing	O
architecture	O
in	O
December	O
1995	O
,	O
but	O
its	O
use	O
was	O
deprecated	O
in	O
September	O
2004	O
because	O
the	O
definition	O
of	O
the	O
term	O
site	O
was	O
ambiguous	O
,	O
which	O
led	O
to	O
confusing	O
routing	B-Protocol
rules	O
.	O
</s>
<s>
The	O
96-bit	O
zero-value	O
prefix	O
,	O
originally	O
known	O
as	O
IPv4-compatible	O
addresses	O
,	O
was	O
mentioned	O
in	O
1995	O
but	O
never	O
fully	O
described	O
.	O
</s>
<s>
This	O
range	O
of	O
addresses	O
was	O
used	O
to	O
represent	O
IPv4	B-Protocol
addresses	O
within	O
an	O
IPv6	B-Protocol
transition	I-Protocol
technology	I-Protocol
.	O
</s>
<s>
Such	O
an	O
IPv6	B-Protocol
address	I-Protocol
has	O
its	O
first	O
(	O
most	O
significant	O
)	O
96	O
bits	O
set	O
to	O
zero	O
,	O
while	O
its	O
last	O
32	O
bits	O
are	O
the	O
IPv4	B-Protocol
address	O
that	O
is	O
represented	O
.	O
</s>
<s>
In	O
February	O
2006	O
,	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
deprecated	O
the	O
use	O
of	O
IPv4-compatible	O
addresses	O
.	O
</s>
<s>
The	O
only	O
remaining	O
use	O
of	O
this	O
address	O
format	O
is	O
to	O
represent	O
an	O
IPv4	B-Protocol
address	O
in	O
a	O
table	O
or	O
database	O
with	O
fixed	O
size	O
members	O
that	O
must	O
also	O
be	O
able	O
to	O
store	O
an	O
IPv6	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Address	O
block	O
was	O
allocated	O
for	O
test	O
purposes	O
for	O
the	O
6bone	B-Protocol
network	O
in	O
December	O
1998	O
.	O
</s>
<s>
Due	O
to	O
operational	O
problems	O
with	O
6to4	B-Protocol
the	O
use	O
of	O
address	O
block	O
is	O
diminishing	O
,	O
since	O
the	O
6to4	B-Protocol
mechanism	O
is	O
deprecated	O
since	O
May	O
2015	O
.	O
</s>
<s>
Although	O
IPv4	B-Protocol
address	O
block	O
is	O
deprecated	O
,	O
is	O
not	O
.	O
</s>
<s>
In	O
April	O
2007	O
the	O
address	O
block	O
was	O
assigned	O
for	O
Overlay	O
Routable	B-Protocol
Cryptographic	O
Hash	B-Error_Name
Identifiers	O
(	O
ORCHID	O
)	O
.	O
</s>
<s>
For	O
reverse	B-Protocol
DNS	I-Protocol
lookup	I-Protocol
,	O
IPv6	B-Protocol
addresses	I-Protocol
were	O
originally	O
registered	O
in	O
the	O
DNS	B-Protocol
zone	O
ip6.int,	O
because	O
it	O
was	O
expected	O
that	O
the	O
top-level	O
domain	O
arpa	O
would	O
be	O
retired	O
.	O
</s>
<s>
Originally	O
,	O
two	O
proposals	O
existed	O
for	O
translating	O
domain	O
names	O
to	O
IPv6	B-Protocol
addresses	I-Protocol
:	O
one	O
using	O
AAAA	O
records	O
,	O
the	O
other	O
using	O
A6	O
records	O
.	O
</s>
<s>
AAAA	O
records	O
,	O
the	O
method	O
that	O
prevailed	O
,	O
are	O
comparable	O
to	O
A	O
records	O
for	O
IPv4	B-Protocol
,	O
providing	O
a	O
simple	O
mapping	O
from	O
hostname	B-Protocol
to	O
IPv6	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
2009	O
,	O
many	O
DNS	B-Protocol
resolvers	O
in	O
home-networking	O
NAT	B-Protocol
devices	I-Protocol
and	O
routers	B-Protocol
were	O
found	O
to	O
handle	O
AAAA	O
records	O
improperly	O
.	O
</s>
<s>
Some	O
of	O
these	O
simply	O
dropped	O
DNS	B-Protocol
requests	O
for	O
such	O
records	O
,	O
instead	O
of	O
properly	O
returning	O
the	O
appropriate	O
negative	O
DNS	B-Protocol
response	O
.	O
</s>
<s>
This	O
often	O
causes	O
a	O
slow-down	O
when	O
connecting	O
to	O
dual-stack	O
IPv6/IPv4	O
hosts	O
,	O
as	O
the	O
client	O
software	O
will	O
wait	O
for	O
the	O
IPv6	B-Protocol
connection	O
to	O
fail	O
before	O
trying	O
IPv4	B-Protocol
.	O
</s>
