<s>
A	O
network	B-Application
extrusion	I-Application
is	O
a	O
kind	O
of	O
VPN	B-Application
tunnel	O
where	O
a	O
subnet	B-Protocol
(	O
or	O
host	O
)	O
is	O
moved	O
to	O
another	O
location	O
,	O
without	O
any	O
router	O
advertisement	O
changes	O
.	O
</s>
<s>
Such	O
a	O
subnet	B-Protocol
is	O
routed	O
to	O
normally	O
,	O
but	O
then	O
send	O
via	O
a	O
VPN	B-Application
tunnel	O
to	O
appear	O
anywhere	O
else	O
on	O
the	O
internet	O
.	O
</s>
<s>
This	O
type	O
of	O
VPN	B-Application
connection	O
is	O
often	O
used	O
for	O
:	O
</s>
<s>
Assigning	O
a	O
static	O
IP	B-Protocol
address	I-Protocol
to	O
a	O
roaming	O
laptop	O
to	O
ensure	O
it	O
is	O
always	O
reachable	O
on	O
1	O
static	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
IPsec/Openswan	O
IPv4	B-Protocol
configuration	O
,	O
this	O
corresponds	O
to	O
a	O
policy	O
on	O
the	O
client	O
system	O
like	O
:	O
</s>
<s>
When	O
this	O
IPsec	B-Protocol
connection	O
is	O
active	O
,	O
the	O
default	O
IP	B-Protocol
address	I-Protocol
for	O
outgoing	O
connections	O
is	O
192.0.0.1	O
.	O
</s>
<s>
Since	O
this	O
is	O
covered	O
by	O
the	O
IPsec	B-Protocol
tunnel	O
,	O
the	O
packet	O
will	O
be	O
encrypted	O
and	O
send	O
to	O
the	O
remote	O
IPsec	B-Protocol
gateway	O
at	O
192.1.0.1	O
.	O
</s>
<s>
When	O
using	O
leftsubnet	O
=	O
192.0.0.0/24	O
,	O
one	O
could	O
even	O
run	O
a	O
small	O
network	O
with	O
the	O
laptop	O
as	O
default	O
gateway	O
and	O
provide	O
public	O
IP	B-Protocol
addresses	I-Protocol
to	O
many	O
computers	O
,	O
all	O
appearing	O
to	O
live	O
at	O
the	O
remote	O
site	O
.	O
</s>
<s>
Generally	O
,	O
IPsec	B-Protocol
VPNs	B-Application
are	O
used	O
in	O
many	O
cases	O
to	O
route	O
private	B-Protocol
networks	I-Protocol
rather	O
than	O
public	O
ones	O
,	O
so	O
while	O
this	O
configuration	O
is	O
not	O
implausible	O
,	O
it	O
is	O
unusual	O
for	O
VPN	B-Application
administrators	O
.	O
</s>
<s>
Many	O
remote	O
access	O
situations	O
run	O
as	O
network	B-Application
extrusions	I-Application
so	O
that	O
a	O
corporate	O
firewall	B-Application
can	O
inspect	O
the	O
traffic	O
that	O
travels	O
to	O
and	O
from	O
the	O
laptop	O
computer	O
.	O
</s>
<s>
These	O
tunnels	O
are	O
invisible	O
to	O
traceroute	B-Protocol
because	O
the	O
IPsec	B-Protocol
tunnel	O
appears	O
as	O
a	O
single	O
additional	O
hop	O
,	O
just	O
like	O
a	O
subnet	B-Protocol
.	O
</s>
