<s>
A	O
DNS	B-Protocol
sinkhole	I-Protocol
,	O
also	O
known	O
as	O
a	O
sinkhole	B-Protocol
server	I-Protocol
,	O
Internet	B-Protocol
sinkhole	I-Protocol
,	O
or	O
Blackhole	O
DNS	B-Protocol
is	O
a	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
server	O
that	O
has	O
been	O
configured	O
to	O
hand	O
out	O
non-routable	O
addresses	O
for	O
a	O
certain	O
set	O
of	O
domain	O
names	O
.	O
</s>
<s>
The	O
higher	O
up	O
the	O
DNS	B-Protocol
resolution	O
chain	O
the	O
sinkhole	O
is	O
,	O
the	O
more	O
requests	O
will	O
fail	O
,	O
because	O
of	O
the	O
greater	O
number	O
of	O
lower	O
nameservers	O
that	O
in	O
turn	O
serve	O
a	O
greater	O
number	O
of	O
clients	O
.	O
</s>
<s>
Some	O
of	O
the	O
larger	O
botnets	B-Architecture
have	O
been	O
made	O
unusable	O
by	O
top-level	O
domain	O
sinkholes	O
that	O
span	O
the	O
entire	O
Internet	O
.	O
</s>
<s>
DNS	B-Protocol
Sinkholes	I-Protocol
are	O
effective	O
at	O
detecting	O
and	O
blocking	O
bots	O
and	O
other	O
malicious	O
traffic	O
.	O
</s>
<s>
By	O
default	O
,	O
the	O
local	O
hosts	B-Protocol
file	I-Protocol
on	O
a	O
computer	O
is	O
checked	O
before	O
DNS	B-Protocol
servers	O
,	O
and	O
can	O
be	O
used	O
to	O
block	O
sites	O
in	O
the	O
same	O
way	O
.	O
</s>
<s>
Sinkholes	O
can	O
be	O
used	O
both	O
constructively	O
,	O
to	O
contain	O
threats	O
such	O
as	O
WannaCry	O
and	O
Avalanche	O
,	O
and	O
destructively	O
,	O
for	O
example	O
disrupting	O
DNS	B-Protocol
services	O
in	O
a	O
DoS	O
attack	O
.	O
</s>
<s>
DNS	B-Protocol
sinkholing	O
can	O
be	O
used	O
to	O
protect	O
users	O
by	O
intercepting	O
DNS	B-Protocol
request	O
attempting	O
to	O
connect	O
to	O
known	O
malicious	O
domains	O
and	O
instead	O
returning	O
an	O
IP	O
address	O
of	O
a	O
sinkhole	B-Protocol
server	I-Protocol
defined	O
by	O
the	O
DNS	B-Protocol
sinkhole	I-Protocol
administrator	O
.	O
</s>
<s>
One	O
example	O
of	O
blocking	O
malicious	O
domains	O
is	O
to	O
stop	O
botnets	B-Architecture
,	O
by	O
interrupting	O
the	O
DNS	B-Protocol
names	I-Protocol
the	O
botnet	B-Architecture
is	O
programmed	O
to	O
use	O
for	O
coordination	O
.	O
</s>
<s>
Another	O
use	O
is	O
to	O
block	O
ad	O
serving	O
sites	O
,	O
either	O
using	O
a	O
hosts	O
file-based	O
sinkhole	O
or	O
by	O
locally	O
running	O
a	O
DNS	B-Protocol
server	O
(	O
e.g.	O
,	O
using	O
a	O
Pi-hole	B-Application
)	O
.	O
</s>
<s>
Local	O
DNS	B-Protocol
servers	O
effectively	O
block	O
ads	O
for	O
all	O
devices	O
on	O
the	O
network	O
.	O
</s>
