<s>
In	O
Internet	O
networking	O
,	O
a	O
private	B-Protocol
network	I-Protocol
is	O
a	O
computer	B-Architecture
network	I-Architecture
that	O
uses	O
a	O
private	B-Protocol
address	I-Protocol
space	O
of	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
These	O
addresses	O
are	O
commonly	O
used	O
for	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
in	O
residential	O
,	O
office	O
,	O
and	O
enterprise	O
environments	O
.	O
</s>
<s>
Both	O
the	O
IPv4	B-Protocol
and	O
the	O
IPv6	B-Protocol
specifications	O
define	O
private	B-Protocol
IP	I-Protocol
address	I-Protocol
ranges	O
.	O
</s>
<s>
Private	B-Protocol
network	I-Protocol
addresses	O
are	O
not	O
allocated	O
to	O
any	O
specific	O
organization	O
.	O
</s>
<s>
Private	B-Protocol
IP	I-Protocol
address	I-Protocol
spaces	O
were	O
originally	O
defined	O
to	O
assist	O
in	O
delaying	O
IPv4	B-Protocol
address	I-Protocol
exhaustion	I-Protocol
.	O
</s>
<s>
IP	O
packets	B-Protocol
originating	O
from	O
or	O
addressed	O
to	O
a	O
private	B-Protocol
IP	I-Protocol
address	I-Protocol
cannot	O
be	O
routed	B-Protocol
through	O
the	O
public	O
Internet	O
.	O
</s>
<s>
The	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
has	O
directed	O
the	O
Internet	O
Assigned	O
Numbers	O
Authority	O
(	O
IANA	O
)	O
to	O
reserve	B-Protocol
the	O
following	O
IPv4	B-Protocol
address	B-General_Concept
ranges	I-General_Concept
for	O
private	B-Protocol
networks	I-Protocol
:	O
</s>
<s>
In	O
April	O
2012	O
,	O
IANA	O
allocated	O
the	O
block	O
100.64.0.0/10	O
(	O
100.64.0.0	O
to	O
100.127.255.255	O
,	O
netmask	O
255.192.0.0	O
)	O
for	O
use	O
in	O
carrier-grade	B-Protocol
NAT	I-Protocol
scenarios	O
.	O
</s>
<s>
This	O
address	O
block	O
should	O
not	O
be	O
used	O
on	O
private	B-Protocol
networks	I-Protocol
or	O
on	O
the	O
public	O
Internet	O
.	O
</s>
<s>
The	O
concept	O
of	O
private	B-Protocol
networks	I-Protocol
has	O
been	O
extended	O
in	O
the	O
next	O
generation	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
IPv6	B-Protocol
,	O
and	O
special	O
address	O
blocks	O
are	O
reserved	O
.	O
</s>
<s>
They	O
are	O
unicast	B-Protocol
addresses	O
,	O
but	O
contain	O
a	O
40-bit	O
random	O
number	O
in	O
the	O
routing	B-Protocol
prefix	O
to	O
prevent	O
collisions	O
when	O
two	O
private	B-Protocol
networks	I-Protocol
are	O
interconnected	O
.	O
</s>
<s>
Despite	O
being	O
inherently	O
local	O
in	O
usage	O
,	O
the	O
IPv6	B-Protocol
address	O
scope	O
of	O
unique	O
local	O
addresses	O
is	O
global	O
.	O
</s>
<s>
The	O
first	O
block	O
defined	O
is	O
,	O
designed	O
for	O
/48	B-Protocol
routing	B-Protocol
blocks	O
,	O
in	O
which	O
users	O
can	O
create	O
multiple	O
subnets	O
,	O
as	O
needed	O
.	O
</s>
<s>
Another	O
type	O
of	O
private	O
networking	O
uses	O
the	O
link-local	O
address	B-General_Concept
range	I-General_Concept
.	O
</s>
<s>
to	O
all	O
computers	O
connected	O
to	O
a	O
switch	B-Protocol
,	O
or	O
to	O
one	O
wireless	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Hosts	O
on	O
different	O
sides	O
of	O
a	O
network	B-Protocol
bridge	I-Protocol
are	O
also	O
on	O
the	O
same	O
link	O
,	O
whereas	O
hosts	O
on	O
different	O
sides	O
of	O
a	O
network	B-Protocol
router	I-Protocol
are	O
on	O
different	O
links	O
.	O
</s>
<s>
In	O
IPv4	B-Protocol
,	O
link-local	O
addresses	O
are	O
codified	O
in	O
RFC	O
6890	O
and	O
RFC	O
3927	O
.	O
</s>
<s>
Their	O
utility	O
is	O
in	O
zero-configuration	B-Application
networking	I-Application
when	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
services	O
are	O
not	O
available	O
and	O
manual	O
configuration	O
by	O
a	O
network	O
administrator	O
is	O
not	O
desirable	O
.	O
</s>
<s>
If	O
a	O
host	O
on	O
an	O
IEEE	O
802	O
(	O
Ethernet	O
)	O
network	O
cannot	O
obtain	O
a	O
network	O
address	O
via	O
DHCP	B-Protocol
,	O
an	O
address	O
from	O
to	O
may	O
be	O
assigned	O
pseudorandomly	O
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
the	O
block	O
is	O
reserved	O
for	O
IP	B-Protocol
address	I-Protocol
autoconfiguration	O
.	O
</s>
<s>
The	O
implementation	O
of	O
these	O
link-local	O
addresses	O
is	O
mandatory	O
,	O
as	O
various	O
functions	O
of	O
the	O
IPv6	B-Protocol
protocol	O
depend	O
on	O
them	O
.	O
</s>
<s>
These	O
addresses	O
are	O
private	O
and	O
link-local	O
by	O
definition	O
,	O
since	O
packets	B-Protocol
never	O
leave	O
the	O
host	O
device	O
.	O
</s>
<s>
IPv4	B-Protocol
reserves	O
the	O
entire	O
class	O
A	O
address	O
block	O
for	O
use	O
as	O
private	O
loopback	O
addresses	O
.	O
</s>
<s>
IPv6	B-Protocol
reserves	O
the	O
single	O
address	O
.	O
</s>
<s>
Private	O
addresses	O
are	O
commonly	O
used	O
in	O
residential	O
IPv4	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
Most	O
Internet	O
service	O
providers	O
(	O
ISPs	O
)	O
allocate	O
only	O
a	O
single	O
publicly	O
routable	B-Protocol
IPv4	B-Protocol
address	O
to	O
each	O
residential	O
customer	O
,	O
but	O
many	O
homes	O
have	O
more	O
than	O
one	O
computer	O
,	O
smartphone	B-Application
,	O
or	O
other	O
Internet-connected	O
device	O
.	O
</s>
<s>
In	O
this	O
situation	O
,	O
a	O
network	B-Protocol
address	I-Protocol
translator	I-Protocol
(	O
NAT/PAT	O
)	O
gateway	O
is	O
usually	O
used	O
to	O
provide	O
Internet	O
connectivity	O
to	O
multiple	O
hosts	O
.	O
</s>
<s>
Private	O
addresses	O
are	O
also	O
commonly	O
used	O
in	O
corporate	B-General_Concept
networks	I-General_Concept
which	O
,	O
for	O
security	O
reasons	O
,	O
are	O
not	O
connected	O
directly	O
to	O
the	O
Internet	O
.	O
</s>
<s>
Often	O
a	O
proxy	O
,	O
SOCKS	B-Application
gateway	O
,	O
or	O
similar	O
devices	O
are	O
used	O
to	O
provide	O
restricted	O
Internet	O
access	O
to	O
network-internal	O
users	O
.	O
</s>
<s>
24-bit	O
block	O
private	O
addresses	O
are	O
also	O
commonly	O
used	O
in	O
the	O
North	O
Korean	O
Kwangmyong	B-Language
network	I-Language
.	O
</s>
<s>
In	O
both	O
cases	O
,	O
private	O
addresses	O
are	O
often	O
seen	O
as	O
enhancing	O
network	O
security	O
for	O
the	O
internal	B-General_Concept
network	I-General_Concept
,	O
since	O
use	O
of	O
private	O
addresses	O
internally	O
makes	O
it	O
difficult	O
for	O
an	O
Internet	O
(	O
external	O
)	O
host	O
to	O
initiate	O
a	O
connection	O
to	O
an	O
internal	O
system	O
.	O
</s>
<s>
It	O
is	O
common	O
for	O
packets	B-Protocol
originating	O
in	O
private	B-Protocol
address	I-Protocol
spaces	O
to	O
be	O
misrouted	O
onto	O
the	O
Internet	O
.	O
</s>
<s>
Private	B-Protocol
networks	I-Protocol
often	O
do	O
not	O
properly	O
configure	O
DNS	O
services	O
for	O
addresses	O
used	O
internally	O
and	O
attempt	O
reverse	B-Protocol
DNS	I-Protocol
lookups	I-Protocol
for	O
these	O
addresses	O
,	O
causing	O
extra	O
traffic	O
to	O
the	O
Internet	O
root	B-Application
nameservers	I-Application
.	O
</s>
<s>
The	O
AS112	O
project	O
attempted	O
to	O
mitigate	O
this	O
load	O
by	O
providing	O
special	O
blackhole	O
anycast	B-Protocol
nameservers	O
for	O
private	B-Protocol
address	I-Protocol
ranges	O
which	O
only	O
return	O
negative	O
result	O
codes	O
(	O
not	O
found	O
)	O
for	O
these	O
queries	O
.	O
</s>
<s>
Organizational	O
edge	B-Protocol
routers	I-Protocol
are	O
usually	O
configured	O
to	O
drop	O
ingress	O
IP	O
traffic	O
for	O
these	O
networks	O
,	O
which	O
can	O
occur	O
either	O
by	O
misconfiguration	O
,	O
or	O
from	O
malicious	O
traffic	O
using	O
a	O
spoofed	O
source	O
address	O
.	O
</s>
<s>
Less	O
commonly	O
,	O
ISP	O
edge	B-Protocol
routers	I-Protocol
drop	O
such	O
egress	O
traffic	O
from	O
customers	O
,	O
which	O
reduces	O
the	O
impact	O
to	O
the	O
Internet	O
of	O
such	O
misconfigured	O
or	O
malicious	O
hosts	O
on	O
the	O
customer	O
's	O
network	O
.	O
</s>
<s>
Since	O
the	O
private	O
IPv4	B-Protocol
address	B-General_Concept
space	I-General_Concept
is	O
relatively	O
small	O
,	O
many	O
private	O
IPv4	B-Protocol
networks	I-Protocol
unavoidably	O
use	O
the	O
same	O
address	B-General_Concept
ranges	I-General_Concept
.	O
</s>
<s>
In	O
this	O
case	O
,	O
networks	O
or	O
hosts	O
must	O
be	O
renumbered	O
,	O
often	O
a	O
time-consuming	O
task	O
,	O
or	O
a	O
network	B-Protocol
address	I-Protocol
translator	I-Protocol
must	O
be	O
placed	O
between	O
the	O
networks	O
to	O
translate	O
or	O
masquerade	O
one	O
of	O
the	O
address	B-General_Concept
ranges	I-General_Concept
.	O
</s>
<s>
IPv6	B-Protocol
defines	O
unique	O
local	O
addresses	O
in	O
RFC	O
4193	O
,	O
providing	O
a	O
very	O
large	O
private	B-Protocol
address	I-Protocol
space	O
from	O
which	O
each	O
organization	O
can	O
randomly	O
or	O
pseudo-randomly	O
allocate	O
a	O
40-bit	O
prefix	O
,	O
each	O
of	O
which	O
allows	O
65536	O
organizational	O
subnets	O
.	O
</s>
<s>
When	O
two	O
such	O
private	O
IPv6	B-Protocol
networks	O
are	O
connected	O
or	O
merged	O
,	O
the	O
risk	O
of	O
an	O
address	O
conflict	O
is	O
therefore	O
virtually	O
absent	O
.	O
</s>
<s>
Despite	O
official	O
warnings	O
,	O
historically	O
some	O
organizations	O
have	O
used	O
other	O
parts	O
of	O
the	O
reserved	B-Protocol
IP	I-Protocol
addresses	I-Protocol
for	O
their	O
internal	B-General_Concept
networks	I-General_Concept
.	O
</s>
