<s>
An	O
Internet	B-Protocol
Protocol	I-Protocol
address	I-Protocol
(	O
IP	B-Protocol
address	I-Protocol
)	O
is	O
a	O
numerical	O
label	O
such	O
as	O
that	O
is	O
connected	O
to	O
a	O
computer	B-Architecture
network	I-Architecture
that	O
uses	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
for	O
communication	O
.	O
</s>
<s>
An	O
IP	B-Protocol
address	I-Protocol
serves	O
two	O
main	O
functions	O
:	O
network	B-Protocol
interface	I-Protocol
identification	O
and	O
location	O
addressing	B-Protocol
.	O
</s>
<s>
Internet	B-Protocol
Protocol	I-Protocol
version	I-Protocol
4	I-Protocol
(	O
IPv4	B-Protocol
)	O
defines	O
an	O
IP	B-Protocol
address	I-Protocol
as	O
a	O
32-bit	O
number	O
.	O
</s>
<s>
However	O
,	O
because	O
of	O
the	O
growth	O
of	O
the	O
Internet	O
and	O
the	O
depletion	B-Protocol
of	I-Protocol
available	I-Protocol
IPv4	I-Protocol
addresses	I-Protocol
,	O
a	O
new	O
version	O
of	O
IP	B-Protocol
(	O
IPv6	B-Protocol
)	O
,	O
using	O
128	O
bits	O
for	O
the	O
IP	B-Protocol
address	I-Protocol
,	O
was	O
standardized	O
in	O
1998	O
.	O
</s>
<s>
IPv6	B-Architecture
deployment	I-Architecture
has	O
been	O
ongoing	O
since	O
the	O
mid-2000s	O
.	O
</s>
<s>
IP	B-Protocol
addresses	I-Protocol
are	O
written	O
and	O
displayed	O
in	O
human-readable	B-General_Concept
notations	O
,	O
such	O
as	O
in	O
IPv4	B-Protocol
,	O
and	O
in	O
IPv6	B-Protocol
.	O
</s>
<s>
The	O
size	O
of	O
the	O
routing	O
prefix	O
of	O
the	O
address	O
is	O
designated	O
in	O
CIDR	B-Protocol
notation	I-Protocol
by	O
suffixing	O
the	O
address	O
with	O
the	O
number	O
of	O
significant	B-Language
bits	I-Language
,	O
e.g.	O
,	O
,	O
which	O
is	O
equivalent	O
to	O
the	O
historically	O
used	O
subnet	B-Protocol
mask	I-Protocol
.	O
</s>
<s>
The	O
IP	B-Protocol
address	I-Protocol
space	O
is	O
managed	O
globally	O
by	O
the	O
Internet	O
Assigned	O
Numbers	O
Authority	O
(	O
IANA	O
)	O
,	O
and	O
by	O
five	O
regional	O
Internet	O
registries	O
(	O
RIRs	O
)	O
responsible	O
in	O
their	O
designated	O
territories	O
for	O
assignment	O
to	O
local	O
Internet	O
registries	O
,	O
such	O
as	O
Internet	O
service	O
providers	O
(	O
ISPs	O
)	O
,	O
and	O
other	O
end	O
users	O
.	O
</s>
<s>
IPv4	B-Protocol
addresses	O
were	O
distributed	O
by	O
IANA	O
to	O
the	O
RIRs	O
in	O
blocks	O
of	O
approximately	O
16.8million	O
addresses	O
each	O
,	O
but	O
have	O
been	O
exhausted	O
at	O
the	O
IANA	O
level	O
since	O
2011	O
.	O
</s>
<s>
Some	O
IPv4	B-Protocol
addresses	O
are	O
reserved	O
for	O
private	B-Protocol
networks	I-Protocol
and	O
are	O
not	O
globally	O
unique	O
.	O
</s>
<s>
Network	O
administrators	O
assign	O
an	O
IP	B-Protocol
address	I-Protocol
to	O
each	O
device	O
connected	O
to	O
a	O
network	O
.	O
</s>
<s>
An	O
IP	B-Protocol
address	I-Protocol
serves	O
two	O
principal	O
functions	O
:	O
it	O
identifies	O
the	O
host	O
,	O
or	O
more	O
specifically	O
its	O
network	B-Protocol
interface	I-Protocol
,	O
and	O
it	O
provides	O
the	O
location	O
of	O
the	O
host	O
in	O
the	O
network	O
,	O
and	O
thus	O
the	O
capability	O
of	O
establishing	O
a	O
path	O
to	O
that	O
host	O
.	O
</s>
<s>
A	O
route	B-Protocol
indicates	O
how	O
to	O
get	O
there.	O
"	O
</s>
<s>
The	O
header	B-General_Concept
of	O
each	O
IP	B-Protocol
packet	I-Protocol
contains	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
sending	O
host	O
and	O
that	O
of	O
the	O
destination	O
host	O
.	O
</s>
<s>
Two	O
versions	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
are	O
in	O
common	O
use	O
on	O
the	O
Internet	O
today	O
.	O
</s>
<s>
The	O
original	O
version	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
that	O
was	O
first	O
deployed	O
in	O
1983	O
in	O
the	O
ARPANET	O
,	O
the	O
predecessor	O
of	O
the	O
Internet	O
,	O
is	O
Internet	B-Protocol
Protocol	I-Protocol
version	I-Protocol
4	I-Protocol
(	O
IPv4	B-Protocol
)	O
.	O
</s>
<s>
By	O
the	O
early	O
1990s	O
,	O
the	O
rapid	O
exhaustion	B-Protocol
of	I-Protocol
IPv4	I-Protocol
address	I-Protocol
space	I-Protocol
available	O
for	O
assignment	O
to	O
Internet	O
service	O
providers	O
and	O
end-user	O
organizations	O
prompted	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
to	O
explore	O
new	O
technologies	O
to	O
expand	O
addressing	B-Protocol
capability	O
on	O
the	O
Internet	O
.	O
</s>
<s>
The	O
result	O
was	O
a	O
redesign	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
which	O
became	O
eventually	O
known	O
as	O
Internet	B-Protocol
Protocol	I-Protocol
Version	I-Protocol
6	I-Protocol
(	O
IPv6	B-Protocol
)	O
in	O
1995	O
.	O
</s>
<s>
IPv6	B-Protocol
technology	O
was	O
in	O
various	O
testing	O
stages	O
until	O
the	O
mid-2000s	O
when	O
commercial	O
production	O
deployment	O
commenced	O
.	O
</s>
<s>
Today	O
,	O
these	O
two	O
versions	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
are	O
in	O
simultaneous	O
use	O
.	O
</s>
<s>
Because	O
of	O
the	O
historical	O
prevalence	O
of	O
IPv4	B-Protocol
,	O
the	O
generic	O
term	O
IP	B-Protocol
address	I-Protocol
typically	O
still	O
refers	O
to	O
the	O
addresses	O
defined	O
by	O
IPv4	B-Protocol
.	O
</s>
<s>
The	O
gap	O
in	O
version	O
sequence	O
between	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
resulted	O
from	O
the	O
assignment	O
of	O
version	O
5	O
to	O
the	O
experimental	O
Internet	B-Protocol
Stream	I-Protocol
Protocol	I-Protocol
in	O
1979	O
,	O
which	O
however	O
was	O
never	O
referred	O
to	O
as	O
IPv5	B-Protocol
.	O
</s>
<s>
v1	O
and	O
v2	O
were	O
names	O
for	O
TCP	B-Protocol
protocols	I-Protocol
in	O
1974	O
and	O
1977	O
,	O
as	O
there	O
was	O
no	O
separate	O
IP	B-Protocol
specification	O
at	O
the	O
time	O
.	O
</s>
<s>
v3	O
was	O
defined	O
in	O
1978	O
,	O
and	O
v3.1	O
is	O
the	O
first	O
version	O
where	O
TCP	O
is	O
separated	O
from	O
IP	B-Protocol
.	O
</s>
<s>
v6	O
is	O
a	O
synthesis	O
of	O
several	O
suggested	O
versions	O
,	O
v6	O
Simple	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
v7	O
TP/IX	O
:	O
The	O
Next	O
Internet	O
,	O
v8	O
PIP	O
—	O
The	O
P	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
and	O
v9	O
TUBA	O
—	O
Tcp	O
&	O
Udp	O
with	O
Big	O
Addresses	O
.	O
</s>
<s>
IP	B-Protocol
networks	I-Protocol
may	O
be	O
divided	O
into	O
subnetworks	B-Protocol
in	O
both	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
.	O
</s>
<s>
For	O
this	O
purpose	O
,	O
an	O
IP	B-Protocol
address	I-Protocol
is	O
recognized	O
as	O
consisting	O
of	O
two	O
parts	O
:	O
the	O
network	O
prefix	O
in	O
the	O
high-order	O
bits	O
and	O
the	O
remaining	O
bits	O
called	O
the	O
rest	O
field	O
,	O
host	O
identifier	O
,	O
or	O
interface	O
identifier	O
(	O
IPv6	B-Protocol
)	O
,	O
used	O
for	O
host	O
numbering	O
within	O
a	O
network	O
.	O
</s>
<s>
The	O
subnet	B-Protocol
mask	I-Protocol
or	O
CIDR	B-Protocol
notation	I-Protocol
determines	O
how	O
the	O
IP	B-Protocol
address	I-Protocol
is	O
divided	O
into	O
network	O
and	O
host	O
parts	O
.	O
</s>
<s>
The	O
term	O
subnet	B-Protocol
mask	I-Protocol
is	O
only	O
used	O
within	O
IPv4	B-Protocol
.	O
</s>
<s>
Both	O
IP	B-Protocol
versions	O
however	O
use	O
the	O
CIDR	B-Protocol
concept	O
and	O
notation	O
.	O
</s>
<s>
In	O
this	O
,	O
the	O
IP	B-Protocol
address	I-Protocol
is	O
followed	O
by	O
a	O
slash	O
and	O
the	O
number	O
(	O
in	O
decimal	O
)	O
of	O
bits	O
used	O
for	O
the	O
network	O
part	O
,	O
also	O
called	O
the	O
routing	O
prefix	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
IPv4	B-Protocol
address	O
and	O
its	O
subnet	B-Protocol
mask	I-Protocol
may	O
be	O
and	O
,	O
respectively	O
.	O
</s>
<s>
The	O
CIDR	B-Protocol
notation	I-Protocol
for	O
the	O
same	O
IP	B-Protocol
address	I-Protocol
and	O
subnet	B-Protocol
is	O
,	O
because	O
the	O
first	O
24	O
bits	O
of	O
the	O
IP	B-Protocol
address	I-Protocol
indicate	O
the	O
network	O
and	O
subnet	B-Protocol
.	O
</s>
<s>
An	O
IPv4	B-Protocol
address	O
has	O
a	O
size	O
of	O
32	O
bits	O
,	O
which	O
limits	O
the	O
address	B-General_Concept
space	I-General_Concept
to	O
(	O
232	O
)	O
addresses	O
.	O
</s>
<s>
Of	O
this	O
number	O
,	O
some	O
addresses	O
are	O
reserved	O
for	O
special	O
purposes	O
such	O
as	O
private	B-Protocol
networks	I-Protocol
(	O
~	O
18million	O
addresses	O
)	O
and	O
multicast	O
addressing	B-Protocol
(	O
~	O
270million	O
addresses	O
)	O
.	O
</s>
<s>
IPv4	B-Protocol
addresses	O
are	O
usually	O
represented	O
in	O
dot-decimal	B-Protocol
notation	I-Protocol
,	O
consisting	O
of	O
four	O
decimal	O
numbers	O
,	O
each	O
ranging	O
from	O
0	O
to	O
255	O
,	O
separated	O
by	O
dots	O
,	O
e.g.	O
,	O
.	O
</s>
<s>
In	O
some	O
cases	O
of	O
technical	O
writing	O
,	O
IPv4	B-Protocol
addresses	O
may	O
be	O
presented	O
in	O
various	O
hexadecimal	O
,	O
octal	O
,	O
or	O
binary	O
representations	O
.	O
</s>
<s>
In	O
the	O
early	O
stages	O
of	O
development	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
the	O
network	O
number	O
was	O
always	O
the	O
highest	O
order	O
octet	O
(	O
most	O
significant	O
eight	O
bits	O
)	O
.	O
</s>
<s>
In	O
1981	O
,	O
the	O
addressing	B-Protocol
specification	O
was	O
revised	O
with	O
the	O
introduction	O
of	O
classful	B-Protocol
network	I-Protocol
architecture	O
.	O
</s>
<s>
Classful	B-Protocol
network	I-Protocol
design	O
allowed	O
for	O
a	O
larger	O
number	O
of	O
individual	O
network	O
assignments	O
and	O
fine-grained	O
subnetwork	B-Protocol
design	O
.	O
</s>
<s>
The	O
first	O
three	O
bits	O
of	O
the	O
most	O
significant	O
octet	O
of	O
an	O
IP	B-Protocol
address	I-Protocol
were	O
defined	O
as	O
the	O
class	O
of	O
the	O
address	O
.	O
</s>
<s>
Three	O
classes	O
(	O
A	O
,	O
B	O
,	O
and	O
C	O
)	O
were	O
defined	O
for	O
universal	O
unicast	B-Protocol
addressing	B-Protocol
.	O
</s>
<s>
Classful	B-Protocol
network	I-Protocol
design	O
served	O
its	O
purpose	O
in	O
the	O
startup	O
stage	O
of	O
the	O
Internet	O
,	O
but	O
it	O
lacked	O
scalability	B-Architecture
in	O
the	O
face	O
of	O
the	O
rapid	O
expansion	O
of	O
networking	O
in	O
the	O
1990s	O
.	O
</s>
<s>
The	O
class	O
system	O
of	O
the	O
address	B-General_Concept
space	I-General_Concept
was	O
replaced	O
with	O
Classless	B-Protocol
Inter-Domain	I-Protocol
Routing	I-Protocol
(	O
CIDR	B-Protocol
)	O
in	O
1993	O
.	O
</s>
<s>
CIDR	B-Protocol
is	O
based	O
on	O
variable-length	B-Protocol
subnet	I-Protocol
masking	I-Protocol
(	O
VLSM	O
)	O
to	O
allow	O
allocation	O
and	O
routing	O
based	O
on	O
arbitrary-length	O
prefixes	O
.	O
</s>
<s>
Today	O
,	O
remnants	O
of	O
classful	B-Protocol
network	I-Protocol
concepts	O
function	O
only	O
in	O
a	O
limited	O
scope	O
as	O
the	O
default	O
configuration	O
parameters	O
of	O
some	O
network	B-Architecture
software	I-Architecture
and	O
hardware	O
components	O
(	O
e.g.	O
</s>
<s>
netmask	B-Protocol
)	O
,	O
and	O
in	O
the	O
technical	O
jargon	O
used	O
in	O
network	O
administrators	O
 '	O
discussions	O
.	O
</s>
<s>
Early	O
network	O
design	O
,	O
when	O
global	O
end-to-end	O
connectivity	O
was	O
envisioned	O
for	O
communications	O
with	O
all	O
Internet	O
hosts	O
,	O
intended	O
that	O
IP	B-Protocol
addresses	I-Protocol
be	O
globally	O
unique	O
.	O
</s>
<s>
However	O
,	O
it	O
was	O
found	O
that	O
this	O
was	O
not	O
always	O
necessary	O
as	O
private	B-Protocol
networks	I-Protocol
developed	O
and	O
public	O
address	B-General_Concept
space	I-General_Concept
needed	O
to	O
be	O
conserved	O
.	O
</s>
<s>
Computers	O
not	O
connected	O
to	O
the	O
Internet	O
,	O
such	O
as	O
factory	O
machines	O
that	O
communicate	O
only	O
with	O
each	O
other	O
via	O
TCP/IP	B-Protocol
,	O
need	O
not	O
have	O
globally	O
unique	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
Today	O
,	O
such	O
private	B-Protocol
networks	I-Protocol
are	O
widely	O
used	O
and	O
typically	O
connect	O
to	O
the	O
Internet	O
with	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
NAT	O
)	O
,	O
when	O
needed	O
.	O
</s>
<s>
Three	O
non-overlapping	O
ranges	O
of	O
IPv4	B-Protocol
addresses	O
for	O
private	B-Protocol
networks	I-Protocol
are	O
reserved	O
.	O
</s>
<s>
These	O
addresses	O
are	O
not	O
routed	O
on	O
the	O
Internet	O
and	O
thus	O
their	O
use	O
need	O
not	O
be	O
coordinated	O
with	O
an	O
IP	B-Protocol
address	I-Protocol
registry	O
.	O
</s>
<s>
Typically	O
,	O
a	O
network	O
administrator	O
will	O
divide	O
a	O
block	O
into	O
subnets	B-Protocol
;	O
for	O
example	O
,	O
many	O
home	B-Application
routers	I-Application
automatically	O
use	O
a	O
default	O
address	B-General_Concept
range	I-General_Concept
of	O
through	O
(	O
)	O
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
the	O
address	O
size	O
was	O
increased	O
from	O
32	O
bits	O
in	O
IPv4	B-Protocol
to	O
128	O
bits	O
,	O
thus	O
providing	O
up	O
to	O
2128	O
(	O
approximately	O
)	O
addresses	O
.	O
</s>
<s>
The	O
intent	O
of	O
the	O
new	O
design	O
was	O
not	O
to	O
provide	O
just	O
a	O
sufficient	O
quantity	O
of	O
addresses	O
,	O
but	O
also	O
redesign	O
routing	O
in	O
the	O
Internet	O
by	O
allowing	O
more	O
efficient	O
aggregation	O
of	O
subnetwork	B-Protocol
routing	O
prefixes	O
.	O
</s>
<s>
This	O
resulted	O
in	O
slower	O
growth	O
of	O
routing	B-Protocol
tables	I-Protocol
in	O
routers	B-Protocol
.	O
</s>
<s>
The	O
smallest	O
possible	O
individual	O
allocation	O
is	O
a	O
subnet	B-Protocol
for	O
264	O
hosts	O
,	O
which	O
is	O
the	O
square	O
of	O
the	O
size	O
of	O
the	O
entire	O
IPv4	B-Protocol
Internet	I-Protocol
.	O
</s>
<s>
At	O
these	O
levels	O
,	O
actual	O
address	O
utilization	O
ratios	O
will	O
be	O
small	O
on	O
any	O
IPv6	B-Protocol
network	O
segment	O
.	O
</s>
<s>
The	O
new	O
design	O
also	O
provides	O
the	O
opportunity	O
to	O
separate	O
the	O
addressing	B-Protocol
infrastructure	O
of	O
a	O
network	O
segment	O
,	O
i.e.	O
</s>
<s>
the	O
local	O
administration	O
of	O
the	O
segment	O
's	O
available	O
space	O
,	O
from	O
the	O
addressing	B-Protocol
prefix	O
used	O
to	O
route	B-Protocol
traffic	O
to	O
and	O
from	O
external	O
networks	O
.	O
</s>
<s>
IPv6	B-Protocol
has	O
facilities	O
that	O
automatically	O
change	O
the	O
routing	O
prefix	O
of	O
entire	O
networks	O
,	O
should	O
the	O
global	O
connectivity	O
or	O
the	O
routing	B-Protocol
policy	I-Protocol
change	O
,	O
without	O
requiring	O
internal	O
redesign	O
or	O
manual	O
renumbering	O
.	O
</s>
<s>
The	O
large	O
number	O
of	O
IPv6	B-Protocol
addresses	O
allows	O
large	O
blocks	O
to	O
be	O
assigned	O
for	O
specific	O
purposes	O
and	O
,	O
where	O
appropriate	O
,	O
to	O
be	O
aggregated	O
for	O
efficient	O
routing	O
.	O
</s>
<s>
With	O
a	O
large	O
address	B-General_Concept
space	I-General_Concept
,	O
there	O
is	O
no	O
need	O
to	O
have	O
complex	O
address	O
conservation	O
methods	O
as	O
used	O
in	O
CIDR	B-Protocol
.	O
</s>
<s>
All	O
modern	O
desktop	O
and	O
enterprise	O
server	O
operating	B-General_Concept
systems	I-General_Concept
include	O
native	O
support	O
for	O
IPv6	B-Protocol
,	O
but	O
it	O
is	O
not	O
yet	O
widely	O
deployed	O
in	O
other	O
devices	O
,	O
such	O
as	O
residential	O
networking	O
routers	B-Protocol
,	O
voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
and	O
multimedia	O
equipment	O
,	O
and	O
some	O
networking	B-Device
hardware	I-Device
.	O
</s>
<s>
Just	O
as	O
IPv4	B-Protocol
reserves	O
addresses	O
for	O
private	B-Protocol
networks	I-Protocol
,	O
blocks	O
of	O
addresses	O
are	O
set	O
aside	O
in	O
IPv6	B-Protocol
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
these	O
are	O
referred	O
to	O
as	O
unique	O
local	O
addresses	O
(	O
ULAs	O
)	O
.	O
</s>
<s>
The	O
addresses	O
include	O
a	O
40-bit	O
pseudorandom	B-Error_Name
number	I-Error_Name
that	O
minimizes	O
the	O
risk	O
of	O
address	O
collisions	O
if	O
sites	O
merge	O
or	O
packets	B-Protocol
are	O
misrouted	O
.	O
</s>
<s>
However	O
,	O
the	O
definition	O
of	O
what	O
constituted	O
a	O
site	O
remained	O
unclear	O
and	O
the	O
poorly	O
defined	O
addressing	B-Protocol
policy	O
created	O
ambiguities	O
for	O
routing	O
.	O
</s>
<s>
The	O
addresses	O
are	O
automatically	O
generated	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
each	O
network	B-Protocol
interface	I-Protocol
.	O
</s>
<s>
This	O
provides	O
instant	O
and	O
automatic	O
communication	O
between	O
all	O
IPv6	B-Protocol
hosts	O
on	O
a	O
link	O
.	O
</s>
<s>
This	O
feature	O
is	O
used	O
in	O
the	O
lower	O
layers	O
of	O
IPv6	B-Protocol
network	O
administration	O
,	O
such	O
as	O
for	O
the	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
Private	O
and	O
link-local	B-Protocol
address	I-Protocol
prefixes	O
may	O
not	O
be	O
routed	O
on	O
the	O
public	O
Internet	O
.	O
</s>
<s>
IP	B-Protocol
addresses	I-Protocol
are	O
assigned	O
to	O
a	O
host	O
either	O
dynamically	O
as	O
they	O
join	O
the	O
network	O
,	O
or	O
persistently	O
by	O
configuration	O
of	O
the	O
host	O
hardware	O
or	O
software	O
.	O
</s>
<s>
Persistent	O
configuration	O
is	O
also	O
known	O
as	O
using	O
a	O
static	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
contrast	O
,	O
when	O
a	O
computer	O
's	O
IP	B-Protocol
address	I-Protocol
is	O
assigned	O
each	O
time	O
it	O
restarts	O
,	O
this	O
is	O
known	O
as	O
using	O
a	O
dynamic	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Dynamic	O
IP	B-Protocol
addresses	I-Protocol
are	O
assigned	O
by	O
network	O
using	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
.	O
</s>
<s>
DHCP	B-Protocol
is	O
the	O
most	O
frequently	O
used	O
technology	O
for	O
assigning	O
addresses	O
.	O
</s>
<s>
It	O
also	O
allows	O
devices	O
to	O
share	O
the	O
limited	O
address	B-General_Concept
space	I-General_Concept
on	O
a	O
network	O
if	O
only	O
some	O
of	O
them	O
are	O
online	O
at	O
a	O
particular	O
time	O
.	O
</s>
<s>
Typically	O
,	O
dynamic	O
IP	B-Protocol
configuration	O
is	O
enabled	O
by	O
default	O
in	O
modern	O
desktop	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
The	O
address	O
assigned	O
with	O
DHCP	B-Protocol
is	O
associated	O
with	O
a	O
lease	O
and	O
usually	O
has	O
an	O
expiration	O
period	O
.	O
</s>
<s>
Some	O
DHCP	B-Protocol
implementations	O
attempt	O
to	O
reassign	O
the	O
same	O
IP	B-Protocol
address	I-Protocol
to	O
a	O
host	O
,	O
based	O
on	O
its	O
MAC	O
address	O
,	O
each	O
time	O
it	O
joins	O
the	O
network	O
.	O
</s>
<s>
A	O
network	O
administrator	O
may	O
configure	O
DHCP	B-Protocol
by	O
allocating	O
specific	O
IP	B-Protocol
addresses	I-Protocol
based	O
on	O
MAC	O
address	O
.	O
</s>
<s>
DHCP	B-Protocol
is	O
not	O
the	O
only	O
technology	O
used	O
to	O
assign	O
IP	B-Protocol
addresses	I-Protocol
dynamically	O
.	O
</s>
<s>
Bootstrap	B-Device
Protocol	I-Device
is	O
a	O
similar	O
protocol	O
and	O
predecessor	O
to	O
DHCP	B-Protocol
.	O
</s>
<s>
Dialup	O
and	O
some	O
broadband	O
networks	O
use	O
dynamic	O
address	O
features	O
of	O
the	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
Computers	O
and	O
equipment	O
used	O
for	O
the	O
network	B-Architecture
infrastructure	I-Architecture
,	O
such	O
as	O
routers	B-Protocol
and	O
mail	O
servers	O
,	O
are	O
typically	O
configured	O
with	O
static	O
addressing	B-Protocol
.	O
</s>
<s>
In	O
the	O
absence	O
or	O
failure	O
of	O
static	O
or	O
dynamic	O
address	O
configurations	O
,	O
an	O
operating	B-General_Concept
system	I-General_Concept
may	O
assign	O
a	O
link-local	B-Protocol
address	I-Protocol
to	O
a	O
host	O
using	O
stateless	B-Protocol
address	I-Protocol
autoconfiguration	I-Protocol
.	O
</s>
<s>
Sticky	O
is	O
an	O
informal	O
term	O
used	O
to	O
describe	O
a	O
dynamically	O
assigned	O
IP	B-Protocol
address	I-Protocol
that	O
seldom	O
changes	O
.	O
</s>
<s>
IPv4	B-Protocol
addresses	O
,	O
for	O
example	O
,	O
are	O
usually	O
assigned	O
with	O
DHCP	B-Protocol
,	O
and	O
a	O
DHCP	B-Protocol
service	O
can	O
use	O
rules	O
that	O
maximize	O
the	O
chance	O
of	O
assigning	O
the	O
same	O
address	O
each	O
time	O
a	O
client	O
asks	O
for	O
an	O
assignment	O
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
a	O
prefix	B-Protocol
delegation	I-Protocol
can	O
be	O
handled	O
similarly	O
,	O
to	O
make	O
changes	O
as	O
rare	O
as	O
feasible	O
.	O
</s>
<s>
In	O
a	O
typical	O
home	O
or	O
small-office	O
setup	O
,	O
a	O
single	O
router	B-Protocol
is	O
the	O
only	O
device	O
visible	O
to	O
an	O
Internet	O
service	O
provider	O
(	O
ISP	O
)	O
,	O
and	O
the	O
ISP	O
may	O
try	O
to	O
provide	O
a	O
configuration	O
that	O
is	O
as	O
stable	O
as	O
feasible	O
,	O
i.e.	O
</s>
<s>
On	O
the	O
local	O
network	O
of	O
the	O
home	O
or	O
business	O
,	O
a	O
local	O
DHCP	B-Protocol
server	I-Protocol
may	O
be	O
designed	O
to	O
provide	O
sticky	O
IPv4	B-Protocol
configurations	O
,	O
and	O
the	O
ISP	O
may	O
provide	O
a	O
sticky	O
IPv6	B-Protocol
prefix	B-Protocol
delegation	I-Protocol
,	O
giving	O
clients	O
the	O
option	O
to	O
use	O
sticky	O
IPv6	B-Protocol
addresses	O
.	O
</s>
<s>
Address	O
block	O
is	O
defined	O
for	O
the	O
special	O
use	O
of	O
link-local	B-Protocol
addressing	I-Protocol
for	O
IPv4	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
every	O
interface	O
,	O
whether	O
using	O
static	O
or	O
dynamic	O
addresses	O
,	O
also	O
receives	O
a	O
link-local	B-Protocol
address	I-Protocol
automatically	O
in	O
the	O
block	O
.	O
</s>
<s>
These	O
addresses	O
are	O
not	O
routable	O
and	O
,	O
like	O
private	O
addresses	O
,	O
cannot	O
be	O
the	O
source	O
or	O
destination	O
of	O
packets	B-Protocol
traversing	O
the	O
Internet	O
.	O
</s>
<s>
When	O
the	O
link-local	O
IPv4	B-Protocol
address	O
block	O
was	O
reserved	O
,	O
no	O
standards	O
existed	O
for	O
mechanisms	O
of	O
address	B-Protocol
autoconfiguration	I-Protocol
.	O
</s>
<s>
Filling	O
the	O
void	O
,	O
Microsoft	O
developed	O
a	O
protocol	O
called	O
Automatic	O
Private	O
IP	B-Protocol
Addressing	I-Protocol
(	O
APIPA	B-Protocol
)	O
,	O
whose	O
first	O
public	O
implementation	O
appeared	O
in	O
Windows	B-Device
98	I-Device
.	O
</s>
<s>
APIPA	B-Protocol
has	O
been	O
deployed	O
on	O
millions	O
of	O
machines	O
and	O
became	O
a	O
de	O
facto	O
standard	O
in	O
the	O
industry	O
.	O
</s>
<s>
An	O
IP	B-Protocol
address	I-Protocol
conflict	O
occurs	O
when	O
two	O
devices	O
on	O
the	O
same	O
local	O
physical	O
or	O
wireless	O
network	O
claim	O
to	O
have	O
the	O
same	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
A	O
second	O
assignment	O
of	O
an	O
address	O
generally	O
stops	O
the	O
IP	B-Protocol
functionality	O
of	O
one	O
or	O
both	O
of	O
the	O
devices	O
.	O
</s>
<s>
Many	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
notify	O
the	O
administrator	O
of	O
IP	B-Protocol
address	I-Protocol
conflicts	O
.	O
</s>
<s>
When	O
IP	B-Protocol
addresses	I-Protocol
are	O
assigned	O
by	O
multiple	O
people	O
and	O
systems	O
with	O
differing	O
methods	O
,	O
any	O
of	O
them	O
may	O
be	O
at	O
fault	O
.	O
</s>
<s>
If	O
one	O
of	O
the	O
devices	O
involved	O
in	O
the	O
conflict	O
is	O
the	O
default	B-Protocol
gateway	I-Protocol
access	O
beyond	O
the	O
LAN	O
for	O
all	O
devices	O
on	O
the	O
LAN	O
,	O
all	O
devices	O
may	O
be	O
impaired	O
.	O
</s>
<s>
IP	B-Protocol
addresses	I-Protocol
are	O
classified	O
into	O
several	O
classes	O
of	O
operational	O
characteristics	O
:	O
unicast	B-Protocol
,	O
multicast	O
,	O
anycast	B-Protocol
and	O
broadcast	B-Operating_System
addressing	B-Protocol
.	O
</s>
<s>
The	O
most	O
common	O
concept	O
of	O
an	O
IP	B-Protocol
address	I-Protocol
is	O
in	O
unicast	B-Protocol
addressing	B-Protocol
,	O
available	O
in	O
both	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
.	O
</s>
<s>
Usually	O
,	O
a	O
unicast	B-Protocol
address	I-Protocol
is	O
associated	O
with	O
a	O
single	O
device	O
or	O
host	O
,	O
but	O
a	O
device	O
or	O
host	O
may	O
have	O
more	O
than	O
one	O
unicast	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Sending	O
the	O
same	O
data	O
to	O
multiple	O
unicast	B-Protocol
addresses	O
requires	O
the	O
sender	O
to	O
send	O
all	O
the	O
data	O
many	O
times	O
over	O
,	O
once	O
for	O
each	O
recipient	O
.	O
</s>
<s>
Broadcasting	B-Operating_System
is	O
an	O
addressing	B-Protocol
technique	O
available	O
in	O
IPv4	B-Protocol
to	O
address	O
data	O
to	O
all	O
possible	O
destinations	O
on	O
a	O
network	O
in	O
one	O
transmission	O
operation	O
as	O
an	O
all-hosts	O
broadcast	B-Operating_System
.	O
</s>
<s>
All	O
receivers	O
capture	O
the	O
network	B-Protocol
packet	I-Protocol
.	O
</s>
<s>
The	O
address	O
is	O
used	O
for	O
network	O
broadcast	B-Operating_System
.	O
</s>
<s>
In	O
addition	O
,	O
a	O
more	O
limited	O
directed	O
broadcast	B-Operating_System
uses	O
the	O
all-ones	O
host	B-Protocol
address	I-Protocol
with	O
the	O
network	O
prefix	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
destination	O
address	O
used	O
for	O
directed	O
broadcast	B-Operating_System
to	O
devices	O
on	O
the	O
network	O
is	O
.	O
</s>
<s>
IPv6	B-Protocol
does	O
not	O
implement	O
broadcast	B-Operating_System
addressing	B-Protocol
and	O
replaces	O
it	O
with	O
multicast	O
to	O
the	O
specially	O
defined	O
all-nodes	O
multicast	B-Protocol
address	I-Protocol
.	O
</s>
<s>
A	O
multicast	B-Protocol
address	I-Protocol
is	O
associated	O
with	O
a	O
group	O
of	O
interested	O
receivers	O
.	O
</s>
<s>
In	O
IPv4	B-Protocol
,	O
addresses	O
through	O
(	O
the	O
former	O
Class	B-Protocol
D	I-Protocol
addresses	O
)	O
are	O
designated	O
as	O
multicast	O
addresses	O
.	O
</s>
<s>
IPv6	B-Protocol
uses	O
the	O
address	O
block	O
with	O
the	O
prefix	O
for	O
multicast	O
.	O
</s>
<s>
In	O
either	O
case	O
,	O
the	O
sender	O
sends	O
a	O
single	O
datagram	B-Protocol
from	O
its	O
unicast	B-Protocol
address	I-Protocol
to	O
the	O
multicast	O
group	O
address	O
and	O
the	O
intermediary	O
routers	B-Protocol
take	O
care	O
of	O
making	O
copies	O
and	O
sending	O
them	O
to	O
all	O
interested	O
receivers	O
(	O
those	O
that	O
have	O
joined	O
the	O
corresponding	O
multicast	O
group	O
)	O
.	O
</s>
<s>
Like	O
broadcast	B-Operating_System
and	O
multicast	O
,	O
anycast	B-Protocol
is	O
a	O
one-to-many	O
routing	O
topology	O
.	O
</s>
<s>
However	O
,	O
the	O
data	O
stream	O
is	O
not	O
transmitted	O
to	O
all	O
receivers	O
,	O
just	O
the	O
one	O
which	O
the	O
router	B-Protocol
decides	O
is	O
closest	O
in	O
the	O
network	O
.	O
</s>
<s>
Anycast	B-Protocol
addressing	B-Protocol
is	O
a	O
built-in	O
feature	O
of	O
IPv6	B-Protocol
.	O
</s>
<s>
In	O
IPv4	B-Protocol
,	O
anycast	B-Protocol
addressing	B-Protocol
is	O
implemented	O
with	O
Border	B-Protocol
Gateway	I-Protocol
Protocol	I-Protocol
using	O
the	O
shortest-path	O
metric	O
to	O
choose	O
destinations	O
.	O
</s>
<s>
Anycast	B-Protocol
methods	O
are	O
useful	O
for	O
global	O
load	B-Application
balancing	I-Application
and	O
are	O
commonly	O
used	O
in	O
distributed	O
DNS	B-Protocol
systems	I-Protocol
.	O
</s>
<s>
A	O
host	O
may	O
use	O
geolocation	B-Application
to	O
deduce	O
the	O
geographic	O
position	O
of	O
its	O
communicating	O
peer	O
.	O
</s>
<s>
A	O
public	O
IP	B-Protocol
address	I-Protocol
is	O
a	O
globally	O
routable	O
unicast	B-Protocol
IP	B-Protocol
address	I-Protocol
,	O
meaning	O
that	O
the	O
address	O
is	O
not	O
an	O
address	O
reserved	O
for	O
use	O
in	O
private	B-Protocol
networks	I-Protocol
,	O
such	O
as	O
those	O
reserved	O
by	O
,	O
or	O
the	O
various	O
IPv6	B-Protocol
address	O
formats	O
of	O
local	O
scope	O
or	O
site-local	O
scope	O
,	O
for	O
example	O
for	O
link-local	B-Protocol
addressing	I-Protocol
.	O
</s>
<s>
Public	O
IP	B-Protocol
addresses	I-Protocol
may	O
be	O
used	O
for	O
communication	O
between	O
hosts	O
on	O
the	O
global	O
Internet	O
.	O
</s>
<s>
In	O
a	O
home	O
situation	O
,	O
a	O
public	O
IP	B-Protocol
address	I-Protocol
is	O
the	O
IP	B-Protocol
address	I-Protocol
assigned	O
to	O
the	O
home	O
's	O
network	O
by	O
the	O
ISP	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
it	O
is	O
also	O
locally	O
visible	O
by	O
logging	O
into	O
the	O
router	B-Protocol
configuration	O
.	O
</s>
<s>
Most	O
public	O
IP	B-Protocol
addresses	I-Protocol
change	O
,	O
and	O
relatively	O
often	O
.	O
</s>
<s>
Any	O
type	O
of	O
IP	B-Protocol
address	I-Protocol
that	O
changes	O
is	O
called	O
a	O
dynamic	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
home	O
networks	O
,	O
the	O
ISP	O
usually	O
assigns	O
a	O
dynamic	O
IP	B-Protocol
.	O
</s>
<s>
If	O
an	O
ISP	O
gave	O
a	O
home	O
network	O
an	O
unchanging	O
address	O
,	O
it	O
's	O
more	O
likely	O
to	O
be	O
abused	O
by	O
customers	O
who	O
host	O
websites	O
from	O
home	O
,	O
or	O
by	O
hackers	B-Application
who	O
can	O
try	O
the	O
same	O
IP	B-Protocol
address	I-Protocol
over	O
and	O
over	O
until	O
they	O
breach	O
a	O
network	O
.	O
</s>
<s>
For	O
security	O
and	O
privacy	O
considerations	O
,	O
network	O
administrators	O
often	O
desire	O
to	O
restrict	O
public	O
Internet	O
traffic	O
within	O
their	O
private	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
The	O
source	O
and	O
destination	O
IP	B-Protocol
addresses	I-Protocol
contained	O
in	O
the	O
headers	B-General_Concept
of	O
each	O
IP	B-Protocol
packet	I-Protocol
are	O
a	O
convenient	O
means	O
to	O
discriminate	O
traffic	O
by	O
IP	B-Protocol
address	I-Protocol
blocking	O
or	O
by	O
selectively	O
tailoring	O
responses	O
to	O
external	O
requests	O
to	O
internal	O
servers	O
.	O
</s>
<s>
This	O
is	O
achieved	O
with	O
firewall	B-Application
software	I-Application
running	O
on	O
the	O
network	O
's	O
gateway	B-Application
router	I-Application
.	O
</s>
<s>
A	O
database	O
of	O
IP	B-Protocol
addresses	I-Protocol
of	O
restricted	O
and	O
permissible	O
traffic	O
may	O
be	O
maintained	O
in	O
blacklists	O
and	O
whitelists	O
,	O
respectively	O
.	O
</s>
<s>
Multiple	O
client	O
devices	O
can	O
appear	O
to	O
share	O
an	O
IP	B-Protocol
address	I-Protocol
,	O
either	O
because	O
they	O
are	O
part	O
of	O
a	O
shared	O
web	O
hosting	O
service	O
environment	O
or	O
because	O
an	O
IPv4	B-Protocol
network	I-Protocol
address	O
translator	O
(	O
NAT	O
)	O
or	O
proxy	B-Application
server	I-Application
acts	O
as	O
an	O
intermediary	O
agent	O
on	O
behalf	O
of	O
the	O
client	O
,	O
in	O
which	O
case	O
the	O
real	O
originating	O
IP	B-Protocol
address	I-Protocol
is	O
masked	O
from	O
the	O
server	O
receiving	O
a	O
request	O
.	O
</s>
<s>
A	O
common	O
practice	O
is	O
to	O
have	O
a	O
NAT	O
mask	O
many	O
devices	O
in	O
a	O
private	B-Protocol
network	I-Protocol
.	O
</s>
<s>
The	O
NAT	B-Protocol
device	I-Protocol
maps	O
different	O
IP	B-Protocol
addresses	I-Protocol
on	O
the	O
private	B-Protocol
network	I-Protocol
to	O
different	O
TCP	O
or	O
UDP	O
port	B-Protocol
numbers	I-Protocol
on	O
the	O
public	O
network	O
.	O
</s>
<s>
In	O
residential	O
networks	O
,	O
NAT	O
functions	O
are	O
usually	O
implemented	O
in	O
a	O
residential	B-Application
gateway	I-Application
.	O
</s>
<s>
In	O
this	O
scenario	O
,	O
the	O
computers	O
connected	O
to	O
the	O
router	B-Protocol
have	O
private	B-Protocol
IP	I-Protocol
addresses	I-Protocol
and	O
the	O
router	B-Protocol
has	O
a	O
public	O
address	O
on	O
its	O
external	O
interface	O
to	O
communicate	O
on	O
the	O
Internet	O
.	O
</s>
<s>
The	O
internal	O
computers	O
appear	O
to	O
share	O
one	O
public	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
provide	O
various	O
diagnostic	O
tools	O
to	O
examine	O
network	O
interfaces	O
and	O
address	O
configuration	O
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
provides	O
the	O
command-line	B-Application
interface	I-Application
tools	O
ipconfig	O
and	O
netsh	O
and	O
users	O
of	O
Unix-like	B-Operating_System
systems	I-Operating_System
may	O
use	O
ifconfig	B-Protocol
,	O
netstat	B-Application
,	O
route	B-Protocol
,	O
lanstat	O
,	O
fstat	B-Language
,	O
and	O
iproute2	B-Protocol
utilities	O
to	O
accomplish	O
the	O
task	O
.	O
</s>
