<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
TUN	O
and	O
TAP	O
are	O
kernel	B-Operating_System
virtual	B-Protocol
network	I-Protocol
devices	O
.	O
</s>
<s>
Being	O
network	O
devices	O
supported	O
entirely	O
in	O
software	O
,	O
they	O
differ	O
from	O
ordinary	O
network	O
devices	O
which	O
are	O
backed	O
by	O
physical	O
network	B-Protocol
adapters	I-Protocol
.	O
</s>
<s>
The	O
Universal	O
TUN/TAP	B-Protocol
Driver	O
originated	O
in	O
2000	O
as	O
a	O
merger	O
of	O
the	O
corresponding	O
drivers	O
in	O
Solaris	B-Application
,	O
Linux	B-Application
and	O
BSD	O
.	O
</s>
<s>
The	O
driver	O
continues	O
to	O
be	O
maintained	O
as	O
part	O
of	O
the	O
Linux	B-Application
and	O
FreeBSD	B-Operating_System
kernels	B-Operating_System
.	O
</s>
<s>
Though	O
both	O
are	O
for	O
tunneling	O
purposes	O
,	O
TUN	O
and	O
TAP	O
ca	O
n't	O
be	O
used	O
together	O
because	O
they	O
transmit	O
and	O
receive	O
packets	O
at	O
different	O
layers	O
of	O
the	O
network	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
TUN	O
,	O
namely	O
network	B-Protocol
TUNnel	I-Protocol
,	O
simulates	O
a	O
network	B-Application
layer	I-Application
device	O
and	O
operates	O
in	O
layer	B-Application
3	I-Application
carrying	O
IP	B-Protocol
packets	O
.	O
</s>
<s>
TAP	O
,	O
namely	O
network	B-Device
TAP	I-Device
,	O
simulates	O
a	O
link	B-Protocol
layer	I-Protocol
device	O
and	O
operates	O
in	O
layer	O
2	O
carrying	O
Ethernet	O
frames	O
.	O
</s>
<s>
TUN	O
is	O
used	O
with	O
routing	B-Protocol
.	O
</s>
<s>
TAP	O
can	O
be	O
used	O
to	O
create	O
a	O
user	B-Operating_System
space	I-Operating_System
network	B-Protocol
bridge	I-Protocol
.	O
</s>
<s>
Packets	O
sent	O
by	O
an	O
operating	B-General_Concept
system	I-General_Concept
via	O
a	O
TUN/TAP	B-Protocol
device	O
are	O
delivered	O
to	O
a	O
user	B-Operating_System
space	I-Operating_System
program	O
which	O
attaches	O
itself	O
to	O
the	O
device	O
.	O
</s>
<s>
A	O
user	B-Operating_System
space	I-Operating_System
program	O
may	O
also	O
pass	O
packets	O
into	O
a	O
TUN/TAP	B-Protocol
device	O
.	O
</s>
<s>
In	O
this	O
case	O
the	O
TUN/TAP	B-Protocol
device	O
delivers	O
(	O
or	O
"	O
injects	O
"	O
)	O
these	O
packets	O
to	O
the	O
operating-system	O
network	B-Protocol
stack	I-Protocol
thus	O
emulating	O
their	O
reception	O
from	O
an	O
external	O
source	O
.	O
</s>
<s>
FreeLAN	B-Application
,	O
open-source	O
,	O
free	O
,	O
multi-platform	O
IPv4	O
,	O
IPv6	B-Protocol
and	O
peer-to-peer	O
VPN	B-Application
software	O
over	O
UDP/IP	B-Protocol
.	O
</s>
<s>
Platforms	O
with	O
TUN/TAP	B-Protocol
drivers	O
include	O
:	O
</s>
