<s>
Route	B-Protocol
poisoning	I-Protocol
is	O
a	O
method	O
to	O
prevent	O
a	O
router	O
from	O
sending	O
packets	B-Protocol
through	O
a	O
route	O
that	O
has	O
become	O
invalid	O
within	O
computer	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
Distance-vector	B-Protocol
routing	I-Protocol
protocols	I-Protocol
in	O
computer	B-Architecture
networks	I-Architecture
use	O
route	B-Protocol
poisoning	I-Protocol
to	O
indicate	O
to	O
other	O
routers	O
that	O
a	O
route	O
is	O
no	O
longer	O
reachable	O
and	O
should	O
not	O
be	O
considered	O
from	O
their	O
routing	O
tables	O
.	O
</s>
<s>
Unlike	O
the	O
split	B-Protocol
horizon	I-Protocol
with	O
poison	B-Protocol
reverse	I-Protocol
,	O
route	B-Protocol
poisoning	I-Protocol
provides	O
for	O
sending	O
updates	O
with	O
unreachable	O
hop	O
counts	O
immediately	O
to	O
all	O
the	O
nodes	O
in	O
the	O
network	O
.	O
</s>
<s>
This	O
makes	O
all	O
nodes	O
on	O
the	O
invalid	O
route	O
seem	O
infinitely	O
distant	O
,	O
preventing	O
any	O
of	O
the	O
routers	O
from	O
sending	O
packets	B-Protocol
over	O
the	O
invalid	O
route	O
.	O
</s>
<s>
Some	O
distance-vector	B-Protocol
routing	I-Protocol
protocols	I-Protocol
,	O
such	O
as	O
RIP	B-Protocol
,	O
use	O
a	O
maximum	O
hop	O
count	O
to	O
determine	O
how	O
many	O
routers	O
the	O
traffic	O
must	O
go	O
through	O
to	O
reach	O
the	O
destination	O
.	O
</s>
<s>
Route	B-Protocol
poisoning	I-Protocol
is	O
a	O
method	O
of	O
quickly	O
forgetting	O
outdated	O
routing	O
information	O
from	O
other	O
router	O
's	O
routing	O
tables	O
by	O
changing	O
its	O
hop	O
count	O
to	O
be	O
unreachable	O
(	O
higher	O
than	O
the	O
maximum	O
number	O
of	O
hops	O
allowed	O
)	O
and	O
sending	O
a	O
routing	O
update	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
RIP	B-Protocol
,	O
the	O
maximum	O
hop	O
count	O
is	O
15	O
,	O
so	O
to	O
perform	O
route	B-Protocol
poisoning	I-Protocol
on	O
a	O
route	O
its	O
hop	O
count	O
is	O
changed	O
to	O
16	O
,	O
deeming	O
it	O
unreachable	O
,	O
and	O
a	O
routing	O
update	O
is	O
sent	O
.	O
</s>
<s>
If	O
these	O
updates	O
are	O
lost	O
,	O
some	O
nodes	O
in	O
the	O
network	O
would	O
not	O
be	O
informed	O
that	O
a	O
route	O
is	O
invalid	O
,	O
so	O
they	O
could	O
attempt	O
to	O
send	O
packets	B-Protocol
over	O
the	O
bad	O
route	O
and	O
cause	O
a	O
problem	O
known	O
as	O
a	O
routing	B-Protocol
loop	I-Protocol
.	O
</s>
<s>
Therefore	O
route	B-Protocol
poisoning	I-Protocol
is	O
used	O
in	O
conjunction	O
with	O
holddowns	B-Protocol
to	O
keep	O
update	O
messages	O
from	O
falsely	O
reinstating	O
the	O
validity	O
of	O
a	O
bad	O
route	O
.	O
</s>
<s>
This	O
prevents	O
routing	B-Protocol
loops	I-Protocol
,	O
improving	O
the	O
overall	O
efficiency	O
of	O
the	O
network	O
.	O
</s>
