<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
policy-based	B-Protocol
routing	I-Protocol
(	O
PBR	O
)	O
is	O
a	O
technique	O
used	O
to	O
make	O
routing	B-Protocol
decisions	O
based	O
on	O
policies	O
set	O
by	O
the	O
network	O
administrator	O
.	O
</s>
<s>
When	O
a	O
router	B-Protocol
receives	O
a	O
packet	O
it	O
normally	O
decides	O
where	O
to	O
forward	O
it	O
based	O
on	O
the	O
destination	O
address	O
in	O
the	O
packet	O
,	O
which	O
is	O
then	O
used	O
to	O
look	O
up	O
an	O
entry	O
in	O
a	O
routing	B-Protocol
table	I-Protocol
.	O
</s>
<s>
This	O
permits	O
routing	B-Protocol
of	O
packets	O
originating	O
from	O
different	O
sources	O
to	O
different	O
networks	O
even	O
when	O
the	O
destinations	O
are	O
the	O
same	O
and	O
can	O
be	O
useful	O
when	O
interconnecting	O
several	O
private	O
networks	O
.	O
</s>
<s>
Policy-based	B-Protocol
routing	I-Protocol
may	O
also	O
be	O
based	O
on	O
the	O
size	O
of	O
the	O
packet	O
,	O
the	O
protocol	O
of	O
the	O
payload	O
,	O
or	O
other	O
information	O
available	O
in	O
a	O
packet	O
header	O
or	O
payload	O
.	O
</s>
<s>
In	O
the	O
Cisco	B-Protocol
IOS	I-Protocol
,	O
PBR	O
is	O
implemented	O
using	O
route	O
maps	O
.	O
</s>
<s>
Linux	O
supports	O
multiple	O
routing	B-Protocol
tables	I-Protocol
since	O
version	O
2.2	O
.	O
</s>
<s>
FreeBSD	O
supports	O
PBR	O
using	O
either	O
IPFW	B-Protocol
,	O
IPFilter	B-Protocol
or	O
OpenBSD	O
's	O
PF	B-Protocol
.	O
</s>
<s>
PBR	O
can	O
be	O
used	O
to	O
redirect	O
traffic	O
to	O
a	O
proxy	O
server	O
by	O
using	O
a	O
PBR-aware	O
L3-switch	O
(	O
router	B-Protocol
)	O
.	O
</s>
