<s>
Query	B-Protocol
flooding	I-Protocol
is	O
a	O
method	O
to	O
search	O
for	O
a	O
resource	O
on	O
a	O
peer-to-peer	O
network	O
.	O
</s>
<s>
Early	O
versions	O
of	O
the	O
Gnutella	B-Protocol
protocol	O
operated	O
by	O
query	B-Protocol
flooding	I-Protocol
;	O
newer	O
versions	O
use	O
more	O
efficient	O
search	O
algorithms	O
.	O
</s>
<s>
If	O
a	O
node	O
wants	O
to	O
find	O
a	O
resource	O
on	O
the	O
network	O
,	O
which	O
may	O
be	O
on	O
a	O
node	O
it	O
does	O
not	O
know	O
about	O
,	O
it	O
could	O
simply	O
broadcast	B-Operating_System
its	O
search	O
query	O
to	O
its	O
immediate	O
neighbours	O
.	O
</s>
<s>
Query	B-Protocol
flooding	I-Protocol
is	O
simple	O
to	O
implement	O
and	O
is	O
practical	O
for	O
small	O
networks	O
with	O
few	O
requests	O
.	O
</s>
<s>
It	O
contacts	O
all	O
reachable	O
nodes	O
in	O
the	O
network	O
and	O
so	O
can	O
precisely	O
determine	O
whether	O
a	O
resource	O
can	O
be	O
found	O
in	O
the	O
network	O
(	O
Freenet	B-Protocol
,	O
for	O
example	O
,	O
only	O
returns	O
a	O
probabilistic	O
result	O
)	O
.	O
</s>
<s>
Version	O
0.6	O
of	O
the	O
Gnutella	B-Protocol
protocol	O
mandates	O
query	O
routing	O
.	O
</s>
<s>
Other	O
file-sharing	O
networks	O
,	O
such	O
as	O
the	O
Kad	O
network	O
,	O
use	O
distributed	B-Operating_System
hash	I-Operating_System
tables	I-Operating_System
to	O
index	O
files	O
and	O
for	O
keyword	O
searches	O
.	O
</s>
<s>
BitTorrent	B-Protocol
creates	O
individual	O
overlay	B-Architecture
networks	I-Architecture
for	O
sharing	O
individual	O
files	O
(	O
or	O
archives	O
)	O
.	O
</s>
<s>
Searches	O
are	O
performed	O
by	O
other	O
mechanisms	O
,	O
such	O
as	O
locating	O
torrent	B-Protocol
files	O
indexed	O
on	O
a	O
website	O
.	O
</s>
<s>
A	O
similar	O
mechanism	O
can	O
be	O
used	O
on	O
the	O
Gnutella	B-Protocol
network	O
with	O
magnet	B-Protocol
links	I-Protocol
.	O
</s>
<s>
For	O
instance	O
Bitzi	O
provides	O
a	O
web	O
interface	O
to	O
search	O
for	O
magnet	B-Protocol
links	I-Protocol
.	O
</s>
<s>
Earlier	O
P2P	O
networks	O
,	O
such	O
as	O
Napster	B-Application
,	O
used	O
a	O
centralized	O
database	O
to	O
locate	O
files	O
.	O
</s>
<s>
This	O
does	O
not	O
have	O
a	O
scaling	B-Architecture
problem	O
,	O
but	O
the	O
central	O
server	O
is	O
a	O
single	O
point	O
of	O
failure	O
.	O
</s>
