<s>
An	O
IPv6	B-Protocol
transition	I-Protocol
mechanism	I-Protocol
is	O
a	O
technology	O
that	O
facilitates	O
the	O
transitioning	B-Architecture
of	O
the	O
Internet	O
from	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
version	I-Protocol
4	I-Protocol
(	O
IPv4	B-Protocol
)	O
infrastructure	O
in	O
use	O
since	O
1983	O
to	O
the	O
successor	O
addressing	O
and	O
routing	O
system	O
of	O
Internet	B-Protocol
Protocol	I-Protocol
Version	I-Protocol
6	I-Protocol
(	O
IPv6	B-Protocol
)	O
.	O
</s>
<s>
As	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
networks	O
are	O
not	O
directly	O
interoperable	O
,	O
transition	O
technologies	O
are	O
designed	O
to	O
permit	O
hosts	O
on	O
either	O
network	O
type	O
to	O
communicate	O
with	O
any	O
other	O
host	O
.	O
</s>
<s>
To	O
meet	O
its	O
technical	O
criteria	O
,	O
IPv6	B-Protocol
must	O
have	O
a	O
straightforward	O
transition	O
plan	O
from	O
the	O
current	O
IPv4	B-Protocol
.	O
</s>
<s>
Some	O
basic	O
IPv6	B-Protocol
transition	I-Protocol
mechanisms	I-Protocol
are	O
defined	O
in	O
RFC	O
4213	O
.	O
</s>
<s>
Stateless	O
IP/ICMP	O
Translation	O
(	O
SIIT	O
)	O
translates	O
between	O
the	O
packet	O
header	O
formats	O
in	O
IPv6	B-Protocol
and	O
IPv4	B-Protocol
.	O
</s>
<s>
The	O
SIIT	O
method	O
defines	O
a	O
class	O
of	O
IPv6	B-Protocol
addresses	O
called	O
IPv4-translated	O
addresses	O
.	O
</s>
<s>
They	O
have	O
the	O
prefix	O
and	O
may	O
be	O
written	O
as	O
,	O
in	O
which	O
the	O
IPv4	B-Protocol
formatted	O
address	O
refers	O
to	O
an	O
IPv6-enabled	O
node	O
.	O
</s>
<s>
The	O
prefix	O
was	O
chosen	O
to	O
yield	O
a	O
zero-valued	O
checksum	B-Algorithm
to	O
avoid	O
changes	O
to	O
the	O
transport	O
protocol	O
header	B-Algorithm
checksum	I-Algorithm
.	O
</s>
<s>
The	O
algorithm	O
can	O
be	O
used	O
in	O
a	O
solution	O
that	O
allows	O
IPv6	B-Protocol
hosts	O
that	O
do	O
not	O
have	O
a	O
permanently	O
assigned	O
IPv4	B-Protocol
address	O
to	O
communicate	O
with	O
IPv4-only	O
hosts	O
.	O
</s>
<s>
SIIT	O
can	O
be	O
viewed	O
as	O
a	O
special	O
case	O
of	O
stateless	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
.	O
</s>
<s>
A	O
tunnel	B-Protocol
broker	I-Protocol
provides	O
IPv6	B-Protocol
connectivity	O
by	O
encapsulating	O
IPv6	B-Protocol
traffic	O
in	O
IPv4	B-Protocol
Internet	I-Protocol
transit	O
links	O
,	O
typically	O
using	O
6in4	B-Protocol
.	O
</s>
<s>
This	O
establishes	O
IPv6	B-Protocol
tunnels	O
within	O
the	O
IPv4	B-Protocol
Internet	I-Protocol
.	O
</s>
<s>
The	O
tunnels	O
may	O
be	O
managed	O
with	O
the	O
Tunnel	B-Protocol
Setup	I-Protocol
Protocol	I-Protocol
(	O
TSP	O
)	O
or	O
AYIYA	B-Protocol
.	O
</s>
<s>
6rd	B-Protocol
is	O
a	O
mechanism	O
to	O
facilitate	O
rapid	O
deployment	O
of	O
the	O
IPv6	B-Protocol
service	O
across	O
IPv4	B-Protocol
infrastructures	O
of	O
Internet	O
service	O
providers	O
(	O
ISPs	O
)	O
.	O
</s>
<s>
It	O
uses	O
stateless	O
address	O
mappings	O
between	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
addresses	O
,	O
and	O
transmits	O
IPv6	B-Protocol
packets	O
across	O
automatic	O
tunnels	O
that	O
follow	O
the	O
same	O
optimized	O
routes	O
between	O
customer	O
nodes	O
as	O
IPv4	B-Protocol
packets	O
.	O
</s>
<s>
It	O
was	O
used	O
for	O
an	O
early	O
large	O
deployment	O
of	O
an	O
IPv6	B-Protocol
service	O
with	O
native	O
addresses	O
during	O
2007	O
(	O
RFC	O
5569	O
)	O
.	O
</s>
<s>
TRT	O
employs	O
DNS	B-Protocol
translation	O
between	O
AAAA	O
and	O
A	B-Protocol
records	I-Protocol
known	O
as	O
DNS-ALG	O
as	O
defined	O
in	O
RFC	O
2694	O
.	O
</s>
<s>
NAT64	B-Protocol
is	O
a	O
mechanism	O
to	O
allow	O
IPv6	B-Protocol
hosts	O
to	O
communicate	O
with	O
IPv4	B-Protocol
servers	O
.	O
</s>
<s>
The	O
NAT64	B-Protocol
server	O
is	O
the	O
endpoint	O
for	O
at	O
least	O
one	O
IPv4	B-Protocol
address	O
and	O
an	O
IPv6	B-Protocol
network	O
segment	O
of	O
32-bits	O
,	O
e.g.	O
,	O
.	O
</s>
<s>
The	O
IPv6	B-Protocol
client	O
embeds	O
the	O
IPv4	B-Protocol
address	O
with	O
which	O
it	O
wishes	O
to	O
communicate	O
using	O
these	O
bits	O
,	O
and	O
sends	O
its	O
packets	O
to	O
the	O
resulting	O
address	O
.	O
</s>
<s>
The	O
NAT64	B-Protocol
server	O
then	O
creates	O
a	O
NAT-mapping	O
between	O
the	O
IPv6	B-Protocol
and	O
the	O
IPv4	B-Protocol
address	O
,	O
allowing	O
them	O
to	O
communicate	O
.	O
</s>
<s>
DNS64	O
describes	O
a	O
DNS	B-Protocol
server	I-Protocol
that	O
when	O
asked	O
for	O
a	O
domain	O
's	O
AAAA	B-Protocol
records	I-Protocol
,	O
but	O
only	O
finds	O
A	B-Protocol
records	I-Protocol
,	O
synthesizes	O
the	O
AAAA	B-Protocol
records	I-Protocol
from	O
the	O
A	B-Protocol
records	I-Protocol
.	O
</s>
<s>
The	O
first	O
part	O
of	O
the	O
synthesized	O
IPv6	B-Protocol
address	O
points	O
to	O
an	O
IPv6/IPv4	O
translator	O
and	O
the	O
second	O
part	O
embeds	O
the	O
IPv4	B-Protocol
address	O
from	O
the	O
A	B-Protocol
record	I-Protocol
.	O
</s>
<s>
The	O
translator	O
in	O
question	O
is	O
usually	O
a	O
NAT64	B-Protocol
server	O
.	O
</s>
<s>
It	O
only	O
works	O
for	O
cases	O
where	O
DNS	B-Protocol
is	O
used	O
to	O
find	O
the	O
remote	O
host	O
address	O
,	O
if	O
IPv4	B-Protocol
literals	O
are	O
used	O
the	O
DNS64	O
server	O
will	O
never	O
be	O
involved	O
.	O
</s>
<s>
Because	O
the	O
DNS64	O
server	O
needs	O
to	O
return	O
records	O
not	O
specified	O
by	O
the	O
domain	O
owner	O
,	O
DNSSEC	B-Protocol
validation	O
against	O
the	O
root	O
will	O
fail	O
in	O
cases	O
where	O
the	O
DNS	B-Protocol
server	I-Protocol
doing	O
the	O
translation	O
is	O
not	O
the	O
domain	O
owner	O
's	O
server	O
.	O
</s>
<s>
ISATAP	O
(	O
Intra-Site	O
Automatic	O
Tunnel	O
Addressing	O
Protocol	O
)	O
is	O
an	O
IPv6	B-Protocol
transition	I-Protocol
mechanism	I-Protocol
meant	O
to	O
transmit	O
IPv6	B-Protocol
packets	O
between	O
dual-stack	O
nodes	O
on	O
top	O
of	O
an	O
IPv4	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Unlike	O
6over4	O
(	O
an	O
older	O
similar	O
protocol	O
using	O
IPv4	B-Protocol
multicast	O
)	O
,	O
ISATAP	O
uses	O
IPv4	B-Protocol
as	O
a	O
virtual	O
nonbroadcast	O
multiple-access	O
network	O
(	O
NBMA	O
)	O
data	O
link	O
layer	O
,	O
so	O
that	O
it	O
does	O
not	O
require	O
the	O
underlying	O
IPv4	B-Protocol
network	I-Protocol
infrastructure	O
to	O
support	O
multicast	O
.	O
</s>
<s>
464XLAT	O
(	O
RFC	O
6877	O
)	O
allows	O
clients	O
on	O
IPv6-only	O
networks	O
to	O
access	O
IPv4-only	O
Internet	O
services	O
,	O
such	O
as	O
Skype	O
.	O
</s>
<s>
The	O
client	O
uses	O
a	O
SIIT	O
translator	O
to	O
convert	O
packets	O
from	O
IPv4	B-Protocol
to	O
IPv6	B-Protocol
.	O
</s>
<s>
These	O
are	O
then	O
sent	O
to	O
a	O
NAT64	B-Protocol
translator	O
which	O
translates	O
them	O
from	O
IPv6	B-Protocol
back	O
into	O
IPv4	B-Protocol
and	O
on	O
to	O
an	O
IPv4-only	O
server	O
.	O
</s>
<s>
The	O
NAT64	B-Protocol
translator	O
,	O
or	O
PLAT	O
(	O
Provider-side	O
transLATor	O
)	O
,	O
must	O
be	O
able	O
to	O
reach	O
both	O
the	O
server	O
and	O
the	O
client	O
(	O
through	O
the	O
CLAT	O
)	O
.	O
</s>
<s>
The	O
use	O
of	O
NAT64	B-Protocol
limits	O
connections	O
to	O
a	O
client-server	O
model	O
using	O
UDP	O
,	O
TCP	O
,	O
and	O
ICMP	B-Protocol
.	O
</s>
<s>
T-Mobile	O
US	O
became	O
IPv6-only	O
using	O
464XLAT	O
.	O
</s>
<s>
Orange	O
Polska	O
began	O
IPv6-only	O
(	O
CLAT/NAT64/DNS	O
)	O
service	O
in	O
September	O
2013	O
,	O
migrating	O
all	O
ADSL	O
,	O
VSLS	O
,	O
and	O
FTTH	B-Architecture
gateways	O
by	O
January	O
2015	O
.	O
</s>
<s>
Android	B-Application
includes	O
a	O
native	O
implementation	O
of	O
CLAT	O
since	O
Jelly	B-Application
Bean	I-Application
4.3	O
,	O
released	O
in	O
2013	O
.	O
</s>
<s>
Windows	B-Operating_System
10	I-Operating_System
has	O
a	O
native	O
WWAN-only	O
implementation	O
of	O
464XLAT	O
for	O
desktop	O
and	O
mobile	O
since	O
the	O
2017	O
Creators	O
Update	O
.	O
</s>
<s>
Apple	O
has	O
implemented	O
DNS64/NAT64	O
since	O
the	O
2015	O
release	O
of	O
MacOS	B-Operating_System
X	I-Operating_System
El	I-Operating_System
Capitan	I-Operating_System
and	O
iOS	B-Operating_System
9	I-Operating_System
,	O
mandating	O
IPv6	B-Protocol
support	O
for	O
all	O
apps	O
.	O
</s>
<s>
clatd	O
is	O
a	O
CLAT	O
implementation	O
for	O
Linux	B-Application
.	O
</s>
<s>
FreeBSD	B-Operating_System
has	O
implemented	O
NAT64	B-Protocol
CLAT	O
since	O
Release	O
12.1	O
.	O
</s>
<s>
Dual-Stack	O
Lite	O
technology	O
does	O
not	O
involve	O
allocating	O
an	O
IPv4	B-Protocol
address	O
to	O
customer-premises	O
equipment	O
(	O
CPE	O
)	O
for	O
providing	O
Internet	O
access	O
.	O
</s>
<s>
The	O
CPE	O
distributes	O
private	B-Protocol
IPv4	I-Protocol
addresses	I-Protocol
for	O
the	O
LAN	O
clients	O
,	O
according	O
to	O
the	O
networking	O
requirement	O
in	O
the	O
local	O
area	O
network	O
.	O
</s>
<s>
The	O
CPE	O
encapsulates	B-Protocol
IPv4	B-Protocol
packets	O
within	O
IPv6	B-Protocol
packets	O
.	O
</s>
<s>
The	O
CPE	O
uses	O
its	O
global	O
IPv6	B-Protocol
connection	O
to	O
deliver	O
the	O
packet	O
to	O
the	O
ISP	O
's	O
carrier-grade	B-Protocol
NAT	I-Protocol
(	O
CGN	O
)	O
,	O
which	O
has	O
a	O
global	O
IPv4	B-Protocol
address	O
.	O
</s>
<s>
The	O
original	O
IPv4	B-Protocol
packet	O
is	O
recovered	O
and	O
NAT	B-Protocol
is	O
performed	O
upon	O
the	O
IPv4	B-Protocol
packet	O
and	O
is	O
routed	O
to	O
the	O
public	O
IPv4	B-Protocol
Internet	I-Protocol
.	O
</s>
<s>
The	O
CGN	O
uniquely	O
identifies	O
traffic	O
flows	O
by	O
recording	O
the	O
CPE	O
public	O
IPv6	B-Protocol
address	O
,	O
the	O
private	O
IPv4	B-Protocol
address	O
,	O
and	O
TCP	O
or	O
UDP	O
port	O
number	O
as	O
a	O
session	O
.	O
</s>
<s>
Lightweight	B-Protocol
4over6	I-Protocol
extends	O
DS-Lite	O
by	O
moving	O
the	O
NAT	B-Protocol
functionality	O
from	O
the	O
ISP	O
side	O
to	O
the	O
CPE	O
,	O
eliminating	O
the	O
need	O
to	O
implement	O
carrier-grade	B-Protocol
NAT	I-Protocol
.	O
</s>
<s>
This	O
is	O
accomplished	O
by	O
allocating	O
a	O
port	O
range	O
for	O
a	O
shared	O
IPv4	B-Protocol
address	O
to	O
each	O
CPE	O
.	O
</s>
<s>
Moving	O
the	O
NAT	B-Protocol
functionality	O
to	O
the	O
CPE	O
allows	O
the	O
ISP	O
to	O
reduce	O
the	O
amount	O
of	O
state	O
tracked	O
for	O
each	O
subscriber	O
,	O
which	O
improves	O
the	O
scalability	O
of	O
the	O
translation	O
infrastructure	O
.	O
</s>
<s>
V4-via-v6	O
routing	O
is	O
a	O
technique	O
where	O
IPv4	B-Protocol
addresses	O
are	O
assigned	O
to	O
end	O
hosts	O
only	O
while	O
intermediate	O
routers	O
are	O
only	O
assigned	O
IPv6	B-Protocol
addresses	O
.	O
</s>
<s>
IPv4	B-Protocol
routes	O
are	O
propagated	O
as	O
usual	O
,	O
and	O
no	O
packet	O
translation	O
or	O
encapsulation	O
is	O
employed	O
,	O
but	O
use	O
an	O
IPv6	B-Protocol
next	O
hop	O
.	O
</s>
<s>
V4-via-v6	O
reduces	O
the	O
amount	O
of	O
management	O
required	O
,	O
since	O
the	O
core	O
network	O
only	O
needs	O
to	O
be	O
assigned	O
IPv6	B-Protocol
addresses	O
,	O
but	O
still	O
requires	O
that	O
the	O
core	O
network	O
be	O
able	O
to	O
forward	O
IPv4	B-Protocol
packets	O
.	O
</s>
<s>
V4-via-v6	O
is	O
defined	O
for	O
the	O
Border	B-Protocol
Gateway	I-Protocol
Protocol	I-Protocol
(	O
BGP	B-Protocol
)	O
and	O
the	O
Babel	B-Protocol
routing	I-Protocol
protocol	I-Protocol
.	O
</s>
<s>
It	O
has	O
been	O
implemented	O
the	O
Bird	B-Protocol
Internet	I-Protocol
routing	I-Protocol
daemon	I-Protocol
and	O
in	O
babeld	O
.	O
</s>
<s>
IPv4	B-Protocol
Residual	I-Protocol
Deployment	I-Protocol
(	O
4rd	B-Protocol
)	O
is	O
an	O
experimental	O
mechanism	O
to	O
facilitate	O
residual	O
deployment	O
of	O
the	O
IPv4	B-Protocol
service	O
across	O
IPv6	B-Protocol
networks	O
.	O
</s>
<s>
Like	O
6rd	B-Protocol
,	O
it	O
uses	O
stateless	O
address	O
mappings	O
between	O
IPv6	B-Protocol
and	O
IPv4	B-Protocol
.	O
</s>
<s>
It	O
supports	O
an	O
extension	O
of	O
IPv4	B-Protocol
addressing	O
based	O
on	O
transport-layer	O
ports	O
.	O
</s>
<s>
This	O
is	O
a	O
stateless	O
variant	O
of	O
the	O
A+P	B-Protocol
model	O
.	O
</s>
<s>
Mapping	B-Protocol
of	I-Protocol
Address	I-Protocol
and	I-Protocol
Port	I-Protocol
(	O
MAP	O
)	O
is	O
a	O
Cisco	O
IPv6	B-Protocol
transition	I-Protocol
proposal	O
which	O
combines	O
A+P	B-Protocol
port	O
address	O
translation	O
with	O
tunneling	O
of	O
the	O
IPv4	B-Protocol
packets	O
over	O
an	O
ISP	O
provider	O
's	O
internal	O
IPv6	B-Protocol
network	O
.	O
</s>
<s>
,	O
MAP-T	B-Protocol
and	O
MAP-E	O
are	O
proposed	O
standards	O
.	O
</s>
<s>
Network	O
Address	O
Translation/Protocol	O
Translation	O
(	O
NAT-PT	B-Protocol
)	O
is	O
defined	O
in	O
RFC	O
2766	O
,	O
but	O
due	O
to	O
numerous	O
problems	O
,	O
it	O
has	O
been	O
obsoleted	O
by	O
RFC	O
4966	O
and	O
deprecated	O
to	O
historic	O
status	O
.	O
</s>
<s>
It	O
is	O
typically	O
used	O
in	O
conjunction	O
with	O
a	O
DNS	B-Protocol
application-level	O
gateway	O
(	O
DNS-ALG	O
)	O
implementation	O
.	O
</s>
<s>
While	O
almost	O
identical	O
to	O
NAT-PT	B-Protocol
,	O
Network	B-Protocol
Address	I-Protocol
Port	I-Protocol
Translation	I-Protocol
+	O
Protocol	O
Translation	O
,	O
which	O
is	O
also	O
described	O
in	O
RFC	O
2766	O
,	O
adds	O
translation	O
of	O
the	O
ports	O
as	O
well	O
as	O
the	O
address	O
.	O
</s>
