<s>
A	O
response	B-Protocol
policy	I-Protocol
zone	I-Protocol
(	O
RPZ	O
)	O
is	O
a	O
mechanism	O
to	O
introduce	O
a	O
customized	O
policy	O
in	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
servers	O
,	O
so	O
that	O
recursive	O
resolvers	O
return	O
possibly	O
modified	O
results	O
.	O
</s>
<s>
Usage	O
of	O
an	O
RPZ	O
is	O
based	O
on	O
DNS	B-Protocol
data	O
feeds	O
,	O
known	O
as	O
zone	B-Protocol
transfer	I-Protocol
,	O
from	O
an	O
RPZ	O
provider	O
to	O
the	O
deploying	O
server	O
.	O
</s>
<s>
With	O
respect	O
to	O
other	O
blocklist	O
methods	O
,	O
such	O
as	O
Google	B-Application
Safe	I-Application
Browsing	I-Application
,	O
the	O
actual	O
blocklist	O
is	O
not	O
managed	O
,	O
not	O
even	O
seen	O
,	O
by	O
the	O
client	O
application	O
.	O
</s>
<s>
Web	O
browsers	O
,	O
and	O
any	O
other	O
client	O
applications	O
which	O
connect	O
to	O
servers	O
on	O
the	O
Internet	O
,	O
need	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
server	O
in	O
order	O
to	O
open	O
the	O
connection	O
.	O
</s>
<s>
The	O
RPZ	O
mechanism	O
was	O
developed	O
by	O
the	O
Internet	O
Systems	O
Consortium	O
led	O
by	O
Paul	O
Vixie	O
as	O
a	O
component	O
of	O
the	O
BIND	B-Protocol
Domain	O
Name	O
Server	O
(	O
DNS	B-Protocol
)	O
.	O
</s>
<s>
It	O
was	O
first	O
available	O
in	O
BIND	B-Protocol
release	O
9.8.1	O
released	O
2010	O
,	O
and	O
first	O
publicly	O
announced	O
at	O
Black	O
Hat	O
in	O
July	O
,	O
2010	O
.	O
</s>
<s>
It	O
is	O
also	O
available	O
in	O
the	O
Unbound	B-Protocol
software	I-Protocol
as	O
of	O
version	O
1.14.0	O
.	O
</s>
<s>
The	O
RPZ	O
mechanism	O
is	O
published	O
as	O
an	O
open	O
and	O
vendor-neutral	O
standard	O
for	O
the	O
interchange	O
of	O
DNS	B-Protocol
Firewall	O
configuration	O
information	O
,	O
allowing	O
other	O
DNS	B-Protocol
resolution	O
software	O
to	O
implement	O
it	O
.	O
</s>
<s>
RPZ	O
was	O
developed	O
as	O
a	O
technology	O
to	O
combat	O
the	O
misuse	O
of	O
the	O
DNS	B-Protocol
by	O
groups	O
and/or	O
persons	O
with	O
malicious	O
intent	O
or	O
other	O
nefarious	O
purposes	O
.	O
</s>
<s>
RPZ	O
extends	O
the	O
use	O
of	O
reputation	O
data	O
into	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
.	O
</s>
<s>
RPZ	O
allows	O
a	O
DNS	B-Protocol
recursive	O
resolver	O
to	O
choose	O
specific	O
actions	O
to	O
be	O
performed	O
for	O
a	O
number	O
of	O
collections	O
of	O
domain	O
name	O
data	O
(	O
zones	O
)	O
.	O
</s>
<s>
For	O
each	O
zone	O
,	O
the	O
DNS	B-Protocol
service	O
may	O
choose	O
to	O
perform	O
full	O
resolution	O
(	O
normal	O
behaviour	O
)	O
,	O
or	O
other	O
actions	O
,	O
including	O
declaring	O
that	O
the	O
requested	O
domain	O
does	O
not	O
exist	O
(	O
technically	O
,	O
NXDOMAIN	O
)	O
,	O
or	O
that	O
the	O
user	O
should	O
visit	O
a	O
different	O
domain	O
(	O
technically	O
,	O
CNAME	O
)	O
,	O
amongst	O
other	O
potential	O
actions	O
.	O
</s>
<s>
As	O
zone	O
information	O
can	O
be	O
obtained	O
from	O
external	O
sources	O
(	O
via	O
a	O
zone	B-Protocol
transfer	I-Protocol
)	O
this	O
allows	O
a	O
DNS	B-Protocol
service	O
to	O
obtain	O
information	O
from	O
an	O
external	O
organisation	O
about	O
domain	O
information	O
and	O
then	O
choose	O
to	O
handle	O
that	O
information	O
in	O
a	O
non-standard	O
manner	O
.	O
</s>
<s>
RPZ	O
is	O
essentially	O
a	O
filtering	O
mechanism	O
,	O
either	O
preventing	O
people	O
from	O
visiting	O
internet	O
domains	O
,	O
or	O
pointing	O
them	O
to	O
other	O
locations	O
by	O
manipulating	O
the	O
DNS	B-Protocol
answers	O
in	O
different	O
ways	O
.	O
</s>
<s>
RPZ	O
provides	O
the	O
opportunity	O
for	O
DNS	B-Protocol
recursive	O
resolver	O
operators	O
to	O
be	O
able	O
to	O
obtain	O
reputational	O
data	O
from	O
external	O
organisations	O
about	O
domains	O
that	O
may	O
be	O
harmful	O
,	O
and	O
then	O
use	O
that	O
information	O
to	O
avoid	O
harm	O
coming	O
to	O
the	O
computers	O
that	O
use	O
the	O
recursive	O
resolver	O
by	O
preventing	O
those	O
computers	O
from	O
visiting	O
the	O
potentially	O
harmful	O
domains	O
.	O
</s>
<s>
Consider	O
that	O
Alice	O
uses	O
a	O
computer	O
which	O
uses	O
a	O
DNS	B-Protocol
service	O
(	O
recursive	O
resolver	O
)	O
which	O
is	O
configured	O
to	O
use	O
RPZ	O
and	O
has	O
access	O
to	O
some	O
source	O
of	O
zone	O
data	O
which	O
lists	O
domains	O
that	O
are	O
believed	O
to	O
be	O
dangerous	O
.	O
</s>
<s>
She	O
does	O
so	O
,	O
but	O
the	O
actual	O
location	O
is	O
not	O
the	O
trusted	O
source	O
that	O
she	O
read	O
but	O
a	O
dangerous	O
location	O
which	O
is	O
known	O
to	O
the	O
DNS	B-Protocol
service	O
.	O
</s>
<s>
As	O
the	O
DNS	B-Protocol
service	O
realizes	O
that	O
the	O
resulting	O
web	O
location	O
is	O
dangerous	O
,	O
instead	O
of	O
informing	O
her	O
computer	O
how	O
to	O
get	O
to	O
it	O
(	O
unmodified	O
response	O
)	O
,	O
it	O
sends	O
information	O
which	O
leads	O
to	O
a	O
safe	O
location	O
.	O
</s>
<s>
Depending	O
on	O
how	O
the	O
DNS	B-Protocol
service	O
configures	O
its	O
policy	O
actions	O
,	O
the	O
modified	O
response	O
can	O
be	O
a	O
fixed	O
page	O
on	O
a	O
web	O
site	O
which	O
informs	O
her	O
of	O
what	O
has	O
happened	O
,	O
or	O
a	O
DNS	B-Protocol
error	I-Protocol
code	O
such	O
as	O
NXDOMAIN	O
or	O
NODATA	O
,	O
or	O
send	O
no	O
response	O
at	O
all	O
.	O
</s>
