<s>
NAT64	B-Protocol
is	O
an	O
IPv6	B-Protocol
transition	I-Protocol
mechanism	I-Protocol
that	O
facilitates	O
communication	O
between	O
IPv6	B-Protocol
and	O
IPv4	B-Protocol
hosts	O
by	O
using	O
a	O
form	O
of	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
NAT	O
)	O
.	O
</s>
<s>
The	O
NAT64	B-Protocol
gateway	O
is	O
a	O
translator	O
between	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
protocols	O
,	O
for	O
which	O
function	O
it	O
needs	O
at	O
least	O
one	O
IPv4	B-Protocol
address	I-Protocol
and	O
an	O
IPv6	B-Protocol
network	O
segment	O
comprising	O
a	O
32-bit	O
address	O
space	O
.	O
</s>
<s>
An	O
IPv6	B-Protocol
client	O
embeds	O
the	O
IPv4	B-Protocol
address	I-Protocol
it	O
wishes	O
to	O
communicate	O
with	O
using	O
the	O
host	O
part	O
of	O
the	O
IPv6	B-Protocol
network	O
segment	O
,	O
resulting	O
in	O
an	O
IPv4-embedded	B-Protocol
IPv6	I-Protocol
addresses	I-Protocol
(	O
hence	O
the	O
32-bit	O
address	O
space	O
in	O
the	O
IPv6	B-Protocol
network	O
segment	O
)	O
,	O
and	O
sends	O
packets	O
to	O
the	O
resulting	O
address	O
.	O
</s>
<s>
The	O
NAT64	B-Protocol
gateway	O
creates	O
a	O
mapping	O
between	O
the	O
IPv6	B-Protocol
and	O
the	O
IPv4	B-Protocol
addresses	O
,	O
which	O
may	O
be	O
manually	O
configured	O
or	O
determined	O
automatically	O
.	O
</s>
<s>
A	O
simple	O
NAT64	B-Protocol
installation	O
may	O
consist	O
of	O
a	O
gateway	O
with	O
two	O
interfaces	O
connected	O
to	O
an	O
IPv4	B-Protocol
network	I-Protocol
and	O
an	O
IPv6	B-Protocol
network	O
,	O
respectively	O
.	O
</s>
<s>
Traffic	O
from	O
the	O
IPv6	B-Protocol
network	O
is	O
routed	O
via	O
the	O
gateway	O
which	O
performs	O
all	O
the	O
necessary	O
translations	O
for	O
transferring	O
packets	O
between	O
the	O
two	O
networks	O
.	O
</s>
<s>
However	O
,	O
the	O
translation	O
is	O
not	O
symmetric	O
,	O
as	O
the	O
IPv6	B-Protocol
address	I-Protocol
space	I-Protocol
is	O
much	O
larger	O
than	O
the	O
IPv4	B-Protocol
address	I-Protocol
space	O
;	O
thus	O
,	O
one-to-one	O
address	O
mapping	O
is	O
not	O
possible	O
.	O
</s>
<s>
The	O
gateway	O
maintains	O
IPv6-to-IPv4	O
address	O
mapping	O
,	O
which	O
may	O
be	O
established	O
with	O
an	O
automatic	O
algorithm	O
(	O
stateless	O
mapping	O
)	O
or	O
with	O
special	O
and	O
manual	O
translations	O
(	O
stateful	O
mapping	O
)	O
when	O
the	O
first	O
packet	O
from	O
the	O
IPv6	B-Protocol
network	O
reaches	O
the	O
NAT64	B-Protocol
gateway	O
.	O
</s>
<s>
Stateless	O
translation	O
is	O
appropriate	O
when	O
a	O
NAT64	B-Protocol
translator	O
is	O
used	O
in	O
front	O
of	O
IPv4-only	O
servers	O
to	O
allow	O
them	O
to	O
be	O
reached	O
by	O
remote	O
IPv6-only	O
clients	O
.	O
</s>
<s>
Stateful	O
translation	O
is	O
suitable	O
for	O
deployment	O
at	O
the	O
client	O
side	O
or	O
at	O
the	O
service	O
provider	O
,	O
allowing	O
IPv6-only	O
client	O
hosts	O
to	O
reach	O
remote	O
IPv4-only	O
nodes	O
.	O
</s>
<s>
In	O
general	O
,	O
NAT64	B-Protocol
is	O
designed	O
to	O
be	O
used	O
when	O
the	O
communication	O
is	O
initiated	O
by	O
IPv6	B-Protocol
hosts	O
.	O
</s>
<s>
Not	O
every	O
type	O
of	O
resource	O
is	O
accessible	O
with	O
NAT64	B-Protocol
.	O
</s>
<s>
Protocols	O
that	O
embed	O
IPv4	B-Protocol
literal	O
addresses	O
,	O
such	O
as	O
SIP	B-Application
and	O
SDP	B-Language
,	O
FTP	B-Protocol
,	O
WebSocket	B-Protocol
,	O
Skype	B-Application
,	O
MSN	O
,	O
and	O
any	O
other	O
content	O
with	O
IPv4	B-Protocol
literals	O
are	O
excluded	O
,	O
but	O
a	O
dual-stacked	O
web	O
proxy	O
allows	O
IPv6-only	O
clients	O
to	O
access	O
even	O
web	O
pages	O
with	O
IPv4	B-Protocol
literals	O
in	O
URLs	O
.	O
</s>
<s>
However	O
,	O
464XLAT	O
,	O
which	O
uses	O
NAT64	B-Protocol
,	O
allows	O
use	O
of	O
such	O
protocols	O
over	O
IPv6-only	O
connections	O
.	O
</s>
<s>
For	O
SIP	B-Application
and	O
FTP	B-Protocol
,	O
the	O
problem	O
can	O
also	O
be	O
solved	O
using	O
an	O
application-level	O
gateway	O
,	O
or	O
using	O
Port	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
with	O
the	O
PREFIX64	O
extension	O
.	O
</s>
