<s>
In	O
a	O
router	B-Protocol
,	O
route	B-Protocol
redistribution	I-Protocol
allows	O
a	O
network	O
that	O
uses	O
one	O
routing	B-Protocol
protocol	I-Protocol
to	O
route	O
traffic	O
dynamically	O
based	O
on	O
information	O
learned	O
from	O
another	O
routing	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
On	O
the	O
Internet	O
,	O
routers	B-Protocol
forward	O
data	B-Protocol
packets	I-Protocol
between	O
computer	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
In	O
order	O
for	O
a	O
router	B-Protocol
to	B-Protocol
determine	I-Protocol
where	I-Protocol
to	I-Protocol
forward	I-Protocol
each	O
packet	B-Protocol
,	O
it	O
may	O
use	O
:	O
</s>
<s>
default	B-Protocol
or	O
static	B-Protocol
routes	I-Protocol
that	O
are	O
manually	O
configured	O
,	O
</s>
<s>
on-demand	O
routing	B-Protocol
,	O
</s>
<s>
Policy-based	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
In	O
a	O
small	O
network	O
such	O
as	O
a	O
home	O
or	O
home	O
office	O
,	O
a	O
default	B-Protocol
route	I-Protocol
is	O
often	O
used	O
to	O
send	O
all	O
traffic	O
to	O
the	O
user	O
's	O
Internet	O
service	O
provider	O
.	O
</s>
<s>
Likewise	O
,	O
medium-sized	O
networks	O
such	O
as	O
branch	O
offices	O
or	O
small	O
Internet	O
service	O
providers	O
may	O
use	O
default	B-Protocol
routes	I-Protocol
for	O
traffic	O
intended	O
for	O
the	O
public	O
Internet	O
.	O
</s>
<s>
But	O
in	O
medium-sized	O
and	O
large	O
networks	O
,	O
routers	B-Protocol
use	O
dynamic	B-Protocol
routing	I-Protocol
protocols	I-Protocol
to	O
determine	O
the	O
best	O
paths	O
to	O
various	O
network	O
destinations	O
.	O
</s>
<s>
Sometimes	O
,	O
a	O
network	O
may	O
use	O
more	O
than	O
one	O
dynamic	B-Protocol
routing	I-Protocol
protocol	I-Protocol
,	O
for	O
example	O
,	O
if	O
two	O
different	O
companies	O
merge	O
or	O
if	O
networking	O
devices	O
from	O
multiple	O
vendors	O
are	O
used	O
.	O
</s>
<s>
In	O
such	O
networks	O
,	O
it	O
is	O
often	O
useful	O
to	O
redistribute	O
information	O
from	O
one	O
routing	B-Protocol
protocol	I-Protocol
into	O
another	O
.	O
</s>
<s>
Route	B-Protocol
redistribution	I-Protocol
may	O
be	O
used	O
to	O
allow	O
different	O
networks	O
belonging	O
to	O
the	O
same	O
company	O
to	O
communicate	O
with	O
each	O
other	O
.	O
</s>
<s>
It	O
may	O
also	O
be	O
used	O
when	O
two	O
companies	O
merge	O
and	O
their	O
networks	O
use	O
different	O
routing	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
And	O
it	O
may	O
be	O
used	O
in	O
conjunction	O
with	O
VRFs	O
or	O
MP-BGP	B-Protocol
.	O
</s>
<s>
If	O
not	O
implemented	O
carefully	O
,	O
route	B-Protocol
redistribution	I-Protocol
may	O
cause	O
routing	B-Protocol
loops	I-Protocol
.	O
</s>
<s>
Each	O
routing	B-Protocol
protocol	I-Protocol
contains	O
loop-avoidance	O
mechanisms	O
,	O
but	O
the	O
information	O
needed	O
for	O
loops	O
to	O
be	O
avoided	O
is	O
lost	O
when	O
routes	O
are	O
redistributed	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
distance-vector	B-Protocol
routing	I-Protocol
protocol	I-Protocol
may	O
prevent	O
loops	O
by	O
the	O
"	O
split-horizon	O
"	O
rule	O
;	O
that	O
is	O
to	O
say	O
,	O
if	O
a	O
router	B-Protocol
learns	O
a	O
route	O
from	O
a	O
particular	O
interface	O
it	O
will	O
not	O
re-advertise	O
the	O
route	O
out	O
the	O
same	O
interface	O
.	O
</s>
<s>
In	O
other	O
words	O
if	O
A	O
learns	O
from	O
B	O
that	O
the	O
path	O
to	O
C	O
is	O
through	O
B	O
then	O
it	O
will	O
not	O
tell	O
B	O
to	O
route	O
packets	B-Protocol
destined	O
for	O
C	O
through	O
A	O
.	O
</s>
<s>
Likewise	O
,	O
a	O
link-state	B-Protocol
routing	I-Protocol
protocol	I-Protocol
may	O
keep	O
a	O
database	O
containing	O
the	O
state	O
of	O
different	O
links	O
in	O
the	O
network	O
,	O
representing	O
a	O
"	O
map	O
"	O
(	O
so	O
to	O
speak	O
)	O
of	O
the	O
network	O
.	O
</s>
<s>
The	O
chance	O
of	O
loops	O
is	O
increased	O
if	O
there	O
are	O
more	O
than	O
one	O
router	B-Protocol
that	O
performs	O
redistribution	O
in	O
the	O
same	O
network	O
,	O
and	O
if	O
redistribution	O
occurs	O
in	O
both	O
directions	O
(	O
for	O
example	O
,	O
both	O
from	O
EIGRP	O
into	O
OSPF	O
and	O
from	O
OSPF	O
into	O
EIGRP	O
)	O
.	O
</s>
