<s>
Sentry	B-Protocol
Firewall	I-Protocol
is	O
a	O
free	O
open-source	B-License
network	B-Application
firewall	I-Application
Linux	B-Application
distribution	I-Application
that	O
was	O
first	O
published	O
in	O
2001	O
and	O
has	O
been	O
the	O
subject	O
of	O
multiple	O
magazine	O
reviews	O
.	O
</s>
<s>
The	O
distribution	O
is	O
particularly	O
notable	O
because	O
it	O
consists	O
solely	O
of	O
a	O
bootable	B-Operating_System
CD-ROM	B-Device
that	O
is	O
designed	O
to	O
be	O
used	O
in	O
a	O
computer	O
with	O
no	O
hard	O
disk	O
.	O
</s>
<s>
Configuration	O
information	O
is	O
retrieved	O
at	O
boot	B-Operating_System
time	I-Operating_System
by	O
automatically	O
searching	O
on	O
an	O
attached	O
floppy	B-Device
disk	I-Device
drive	I-Device
,	O
USB	O
flash	O
memory	O
drive	O
,	O
or	O
another	O
server	O
on	O
the	O
local	O
network	O
willing	O
to	O
provide	O
the	O
configuration	O
.	O
</s>
<s>
Sentry	B-Protocol
Firewall	I-Protocol
starts	O
from	O
CD-ROM	B-Device
and	O
immediately	O
constructs	O
a	O
RAM	B-Application
disk	I-Application
in	O
the	O
computer	O
's	O
memory	O
.	O
</s>
<s>
If	O
that	O
file	O
is	O
found	O
,	O
it	O
may	O
contain	O
detailed	O
instructions	O
and	O
a	O
list	O
of	O
files	O
to	O
be	O
copied	O
from	O
the	O
removable	O
media	O
to	O
the	O
RAM	B-Application
disk	I-Application
before	O
the	O
system	O
is	O
finally	O
allowed	O
to	O
boot	B-Operating_System
.	O
</s>
<s>
The	O
CD-ROM	B-Device
is	O
pre-loaded	O
with	O
a	O
variety	O
of	O
configurable	O
network	O
tools	O
,	O
including	O
iptables	B-Application
.	O
</s>
<s>
Because	O
the	O
RAM	B-Application
disk	I-Application
is	O
created	O
each	O
time	O
the	O
machine	O
boots	O
,	O
it	O
is	O
possible	O
to	O
recover	O
from	O
any	O
sort	O
of	O
problem	O
simply	O
by	O
rebooting	O
the	O
machine	O
.	O
</s>
<s>
From	O
a	O
security	O
perspective	O
,	O
this	O
is	O
compelling	O
because	O
the	O
machine	O
essentially	O
becomes	O
immune	O
to	O
viruses	O
or	O
file	O
corruption	O
-	O
or	O
at	O
least	O
the	O
effects	O
of	O
either	O
problem	O
ca	O
n't	O
survive	O
a	O
reboot	B-Operating_System
.	O
</s>
<s>
While	O
basic	O
Linux	O
familiarity	O
is	O
necessary	O
to	O
configure	O
a	O
basic	O
set	O
of	O
files	O
necessary	O
to	O
use	O
the	O
firewall	B-Application
,	O
there	O
exists	O
Windows	O
programs	O
capable	O
of	O
creating	O
the	O
bulk	O
of	O
the	O
configuration	O
scripts	O
based	O
on	O
interaction	O
with	O
a	O
graphical	O
user	O
interface	O
.	O
</s>
<s>
is	O
one	O
such	O
example	O
;	O
this	O
program	O
also	O
works	O
with	O
other	O
firewall	B-Application
products	O
unrelated	O
to	O
Sentry	B-Protocol
Firewall	I-Protocol
.	O
</s>
<s>
According	O
to	O
the	O
project	O
's	O
maintainer	O
,	O
Sentry	B-Protocol
Firewall	I-Protocol
has	O
not	O
been	O
updated	O
since	O
its	O
January	O
2005	O
release	O
.	O
</s>
