<s>
A	O
bastion	B-Protocol
host	I-Protocol
is	O
a	O
special-purpose	O
computer	O
on	O
a	O
network	O
specifically	O
designed	O
and	O
configured	O
to	O
withstand	O
attacks	O
,	O
so	O
named	O
by	O
analogy	O
to	O
the	O
military	B-Application
fortification	I-Application
.	O
</s>
<s>
The	O
computer	O
generally	O
hosts	O
a	O
single	O
application	O
or	O
process	O
,	O
for	O
example	O
,	O
a	O
proxy	B-Application
server	I-Application
or	O
load	O
balancer	O
,	O
and	O
all	O
other	O
services	O
are	O
removed	O
or	O
limited	O
to	O
reduce	O
the	O
threat	O
to	O
the	O
computer	O
.	O
</s>
<s>
It	O
is	O
hardened	O
in	O
this	O
manner	O
primarily	O
due	O
to	O
its	O
location	O
and	O
purpose	O
,	O
which	O
is	O
either	O
on	O
the	O
outside	O
of	O
a	O
firewall	B-Application
or	O
inside	O
of	O
a	O
demilitarized	B-General_Concept
zone	I-General_Concept
(	O
DMZ	B-General_Concept
)	O
and	O
usually	O
involves	O
access	O
from	O
untrusted	O
networks	O
or	O
computers	O
.	O
</s>
<s>
The	O
term	O
is	O
generally	O
attributed	O
to	O
a	O
1990	O
article	O
discussing	O
firewalls	B-Application
by	O
Marcus	O
J	O
.	O
Ranum	O
,	O
who	O
defined	O
a	O
bastion	B-Protocol
host	I-Protocol
as	O
"	O
a	O
system	O
identified	O
by	O
the	O
firewall	B-Application
administrator	O
as	O
a	O
critical	O
strong	O
point	O
in	O
the	O
network	O
security	O
.	O
</s>
<s>
Generally	O
,	O
bastion	B-Protocol
hosts	I-Protocol
will	O
have	O
some	O
degree	O
of	O
extra	O
attention	O
paid	O
to	O
their	O
security	O
,	O
may	O
undergo	O
regular	O
audits	O
,	O
and	O
may	O
have	O
modified	O
software	O
"	O
.	O
</s>
<s>
It	O
has	O
also	O
been	O
described	O
as	O
"	O
any	O
computer	O
that	O
is	O
fully	O
exposed	O
to	O
attack	O
by	O
being	O
on	O
the	O
public	O
side	O
of	O
the	O
DMZ	B-General_Concept
,	O
unprotected	O
by	O
a	O
firewall	B-Application
or	O
filtering	O
router	O
.	O
</s>
<s>
Firewalls	B-Application
and	O
routers	O
,	O
anything	O
that	O
provides	O
perimeter	O
access	O
control	O
security	O
can	O
be	O
considered	O
bastion	B-Protocol
hosts	I-Protocol
.	O
</s>
<s>
Other	O
types	O
of	O
bastion	B-Protocol
hosts	I-Protocol
can	O
include	O
web	O
,	O
mail	O
,	O
DNS	B-Protocol
,	O
and	O
FTP	O
servers	O
.	O
</s>
<s>
Due	O
to	O
their	O
exposure	O
,	O
a	O
great	O
deal	O
of	O
effort	O
must	O
be	O
put	O
into	O
designing	O
and	O
configuring	O
bastion	B-Protocol
hosts	I-Protocol
to	O
minimize	O
the	O
chances	O
of	O
penetration.	O
"	O
</s>
<s>
There	O
are	O
two	O
common	O
network	O
configurations	O
that	O
include	O
bastion	B-Protocol
hosts	I-Protocol
and	O
their	O
placement	O
.	O
</s>
<s>
The	O
first	O
requires	O
two	O
firewalls	B-Application
,	O
with	O
bastion	B-Protocol
hosts	I-Protocol
sitting	O
between	O
the	O
first	O
"	O
outside	O
world	O
"	O
firewall	B-Application
,	O
and	O
an	O
inside	O
firewall	B-Application
,	O
in	O
a	O
DMZ	B-General_Concept
.	O
</s>
<s>
Often	O
,	O
smaller	O
networks	O
do	O
not	O
have	O
multiple	O
firewalls	B-Application
,	O
so	O
if	O
only	O
one	O
firewall	B-Application
exists	O
in	O
a	O
network	O
,	O
bastion	B-Protocol
hosts	I-Protocol
are	O
commonly	O
placed	O
outside	O
the	O
firewall	B-Application
.	O
</s>
<s>
These	O
are	O
several	O
examples	O
of	O
bastion	B-Protocol
host	I-Protocol
systems/services	O
:	O
</s>
