<s>
ISATAP	B-Protocol
(	O
intra-site	O
automatic	O
tunnel	O
addressing	O
protocol	O
)	O
is	O
an	O
IPv6	B-Protocol
transition	O
mechanism	O
meant	O
to	O
transmit	O
IPv6	B-Protocol
packets	B-Protocol
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	B-Protocol
(	O
an	O
older	O
similar	O
protocol	O
using	O
IPv4	B-Protocol
multicast	O
)	O
,	O
ISATAP	B-Protocol
uses	O
IPv4	B-Protocol
as	O
a	O
virtual	O
non-broadcast	B-Protocol
multiple-access	I-Protocol
network	I-Protocol
(	O
NBMA	B-Protocol
)	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
,	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>
ISATAP	B-Protocol
typically	O
builds	O
its	O
PRL	O
by	O
consulting	O
the	O
DNS	O
;	O
hence	O
,	O
in	O
the	O
OSI	O
model	O
it	O
is	O
a	O
lower-layer	O
protocol	O
that	O
relies	O
on	O
a	O
higher	O
layer	O
.	O
</s>
<s>
A	O
circularity	O
is	O
avoided	O
by	O
relying	O
on	O
an	O
IPv4	B-Protocol
DNS	O
server	O
,	O
which	O
does	O
not	O
rely	O
on	O
IPv6	B-Protocol
routing	O
being	O
established	O
;	O
however	O
,	O
some	O
network	O
specialists	O
claim	O
that	O
these	O
violations	O
lead	O
to	O
insufficient	O
protocol	O
robustness	O
.	O
</s>
<s>
ISATAP	B-Protocol
carries	O
the	O
same	O
security	O
risks	O
as	O
6over4	B-Protocol
:	O
the	O
IPv4	B-Protocol
virtual	O
link	O
must	O
be	O
delimited	O
carefully	O
at	O
the	O
network	O
edge	O
,	O
so	O
that	O
external	O
IPv4	B-Protocol
hosts	O
cannot	O
pretend	O
to	O
be	O
part	O
of	O
the	O
ISATAP	B-Protocol
link	O
.	O
</s>
<s>
That	O
is	O
normally	O
done	O
by	O
ensuring	O
that	O
proto-41	O
(	O
6in4	B-Protocol
)	O
cannot	O
pass	O
through	O
the	O
firewall	B-Application
.	O
</s>
<s>
ISATAP	B-Protocol
is	O
implemented	O
in	O
Microsoft	B-Application
Windows	I-Application
XP	I-Application
,	O
Windows	B-Application
Vista	I-Application
,	O
Windows	B-Device
7	I-Device
,	O
Windows	B-Application
8	I-Application
,	O
Windows	B-Operating_System
10	I-Operating_System
,	O
Windows	B-Device
Server	I-Device
2008	I-Device
,	O
Windows	B-Device
Server	I-Device
2012	I-Device
,	O
Windows	B-Device
Server	I-Device
2016	I-Device
,	O
Windows	B-Device
Server	I-Device
2019	I-Device
,	O
Windows	B-Operating_System
Mobile	I-Operating_System
,	O
Linux	B-Application
,	O
and	O
in	O
Cisco	B-Protocol
IOS	I-Protocol
(	O
since	O
IOS	B-Protocol
12.2(14 )	O
S	O
and	O
IOS	B-Protocol
XE	O
Release	O
2.1	O
)	O
.	O
</s>
<s>
Due	O
to	O
a	O
patent	O
claim	O
,	O
early	O
in-kernel	O
implementations	O
were	O
withdrawn	O
from	O
both	O
KAME	B-Application
( *	O
BSD	B-Operating_System
)	O
and	O
USAGI	O
(	O
Linux	B-Application
)	O
.	O
</s>
<s>
ISATAP	B-Protocol
support	O
has	O
been	O
supported	O
in	O
Linux	B-Application
since	O
kernel	B-Operating_System
version	O
2.6.25	O
,	O
the	O
tool	O
isatapd	O
provides	O
a	O
userspace	O
helper	O
.	O
</s>
<s>
For	O
prior	O
kernels	B-Operating_System
,	O
the	O
open	O
source	O
project	O
Miredo	B-Protocol
provided	O
an	O
incomplete	O
userland	O
ISATAP	B-Protocol
implementation	O
,	O
which	O
was	O
removed	O
in	O
version	O
1.1.6	O
.	O
</s>
