<s>
Flooding	B-Protocol
is	O
used	O
in	O
computer	B-Architecture
networks	I-Architecture
routing	B-Protocol
algorithm	I-Protocol
in	O
which	O
every	O
incoming	O
packet	B-Protocol
is	O
sent	O
through	O
every	O
outgoing	O
link	O
except	O
the	O
one	O
it	O
arrived	O
on	O
.	O
</s>
<s>
Flooding	B-Protocol
is	O
used	O
in	O
bridging	B-Protocol
and	O
in	O
systems	O
such	O
as	O
Usenet	B-Application
and	O
peer-to-peer	O
file	O
sharing	O
and	O
as	O
part	O
of	O
some	O
routing	B-Protocol
protocols	I-Protocol
,	O
including	O
OSPF	B-Protocol
,	O
DVMRP	B-Protocol
,	O
and	O
those	O
used	O
in	O
ad-hoc	B-General_Concept
wireless	I-General_Concept
networks	I-General_Concept
(	O
WANETs	B-General_Concept
)	O
.	O
</s>
<s>
There	O
are	O
generally	O
two	O
types	O
of	O
flooding	B-Protocol
available	O
,	O
uncontrolled	O
flooding	B-Protocol
and	O
controlled	O
flooding	B-Protocol
.	O
</s>
<s>
In	O
uncontrolled	O
flooding	B-Protocol
each	O
node	O
unconditionally	O
distributes	O
packets	B-Protocol
to	O
each	O
of	O
its	O
neighbors	O
.	O
</s>
<s>
Without	O
conditional	O
logic	O
to	O
prevent	O
indefinite	O
recirculation	O
of	O
the	O
same	O
packet	B-Protocol
,	O
broadcast	B-General_Concept
storms	I-General_Concept
are	O
a	O
hazard	O
.	O
</s>
<s>
Controlled	O
flooding	B-Protocol
has	O
its	O
own	O
two	O
algorithms	O
to	O
make	O
it	O
reliable	O
,	O
SNCF	O
(	O
Sequence	O
Number	O
Controlled	O
Flooding	B-Protocol
)	O
and	O
RPF	O
(	O
reverse-path	B-Protocol
forwarding	I-Protocol
)	O
.	O
</s>
<s>
In	O
SNCF	O
,	O
the	O
node	O
attaches	O
its	O
own	O
address	O
and	O
sequence	O
number	O
to	O
the	O
packet	B-Protocol
,	O
since	O
every	O
node	O
has	O
a	O
memory	O
of	O
addresses	O
and	O
sequence	O
numbers	O
.	O
</s>
<s>
If	O
it	O
receives	O
a	O
packet	B-Protocol
in	O
memory	O
,	O
it	O
drops	O
it	O
immediately	O
while	O
in	O
RPF	O
,	O
the	O
node	O
will	O
only	O
send	O
the	O
packet	B-Protocol
forward	O
.	O
</s>
<s>
There	O
are	O
several	O
variants	O
of	O
flooding	B-Protocol
algorithms	O
.	O
</s>
<s>
A	O
variant	O
of	O
flooding	B-Protocol
called	O
selective	O
flooding	B-Protocol
partially	O
addresses	O
these	O
issues	O
by	O
only	O
sending	O
packets	B-Protocol
to	O
routers	O
in	O
the	O
same	O
direction	O
.	O
</s>
<s>
In	O
selective	O
flooding	B-Protocol
,	O
the	O
routers	O
do	O
n't	O
send	O
every	O
incoming	O
packet	B-Protocol
on	O
every	O
line	O
but	O
only	O
on	O
those	O
lines	O
which	O
are	O
going	O
approximately	O
in	O
the	O
right	O
direction	O
.	O
</s>
<s>
if	O
a	O
packet	B-Protocol
can	O
be	O
delivered	O
then	O
it	O
will	O
(	O
probably	O
multiple	O
times	O
)	O
,	O
and	O
since	O
flooding	B-Protocol
naturally	O
utilizes	O
every	O
path	O
through	O
the	O
network	O
it	O
will	O
also	O
use	O
the	O
shortest	O
path	O
.	O
</s>
<s>
Flooding	B-Protocol
can	O
be	O
costly	O
in	O
terms	O
of	O
wasted	O
bandwidth	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
ping	B-General_Concept
flood	I-General_Concept
or	O
a	O
denial	O
of	O
service	O
attack	O
,	O
it	O
can	O
be	O
harmful	O
to	O
the	O
reliability	O
of	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
Duplicate	O
packets	B-Protocol
may	O
circulate	O
forever	O
,	O
unless	O
certain	O
precautions	O
are	O
taken	O
:	O
</s>
<s>
Use	O
a	O
hop	B-Protocol
count	I-Protocol
or	O
a	O
time	B-Protocol
to	I-Protocol
live	I-Protocol
(	O
TTL	O
)	O
count	O
and	O
include	O
it	O
with	O
each	O
packet	B-Protocol
.	O
</s>
<s>
This	O
value	O
should	O
take	O
into	O
account	O
the	O
number	O
of	O
nodes	O
that	O
a	O
packet	B-Protocol
may	O
have	O
to	O
pass	O
through	O
on	O
the	O
way	O
to	O
its	O
destination	O
.	O
</s>
<s>
Have	O
each	O
node	O
keep	O
track	O
of	O
every	O
packet	B-Protocol
seen	O
and	O
only	O
forward	O
each	O
packet	B-Protocol
once	O
.	O
</s>
<s>
Enforce	O
a	O
network	B-Architecture
topology	I-Architecture
without	O
loops	O
.	O
</s>
<s>
In	O
Open	B-Protocol
Shortest	I-Protocol
Path	I-Protocol
First	I-Protocol
(	O
OSPF	B-Protocol
)	O
,	O
flooding	B-Protocol
is	O
used	O
for	O
transferring	O
updates	O
to	O
the	O
topology	B-Architecture
(	O
LSAs	O
)	O
.	O
</s>
<s>
In	O
low	O
data	O
rate	O
communications	O
,	O
flooding	B-Protocol
can	O
achieve	O
fast	O
and	O
robust	O
data	O
communications	O
in	O
dedicated	O
protocols	O
such	O
as	O
VEmesh	O
,	O
which	O
operates	O
in	O
the	O
Sub-1GHz	O
frequency	O
band	O
and	O
Bluetooth	O
mesh	O
networking	O
,	O
which	O
operates	O
in	O
the	O
2.4GHz	O
frequency	O
band	O
.	O
</s>
