<s>
A	O
virtual	B-Operating_System
IP	I-Operating_System
address	I-Operating_System
(	O
VIP	O
or	O
VIPA	O
)	O
is	O
an	O
IP	B-Protocol
address	I-Protocol
that	O
does	O
not	O
correspond	O
to	O
a	O
physical	O
network	O
interface	O
.	O
</s>
<s>
Uses	O
for	O
VIPs	O
include	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
especially	O
,	O
one-to-many	O
NAT	O
)	O
,	O
fault-tolerance	O
,	O
and	O
mobility	O
.	O
</s>
<s>
For	O
one-to-many	O
NAT	O
,	O
a	O
VIP	B-Operating_System
address	I-Operating_System
is	O
advertised	O
from	O
the	O
NAT	B-Protocol
device	I-Protocol
(	O
often	O
a	O
router	O
)	O
,	O
and	O
incoming	O
data	O
packets	O
destined	O
to	O
that	O
VIP	B-Operating_System
address	I-Operating_System
are	O
routed	O
to	O
different	O
actual	O
IP	B-Protocol
addresses	I-Protocol
(	O
with	O
address	O
translation	O
)	O
.	O
</s>
<s>
These	O
VIP	O
addresses	O
have	O
several	O
variations	O
and	O
implementation	O
scenarios	O
,	O
including	O
Common	B-Application
Address	I-Application
Redundancy	I-Application
Protocol	I-Application
(	O
CARP	O
)	O
and	O
Proxy	B-Protocol
ARP	I-Protocol
.	O
</s>
<s>
In	O
addition	O
,	O
if	O
there	O
are	O
multiple	O
actual	O
IP	B-Protocol
addresses	I-Protocol
,	O
load	B-Application
balancing	I-Application
can	O
be	O
performed	O
as	O
part	O
of	O
NAT	O
.	O
</s>
<s>
For	O
this	O
to	O
work	O
,	O
the	O
host	O
has	O
to	O
run	O
an	O
interior	O
gateway	O
protocol	O
like	O
Open	B-Protocol
Shortest	I-Protocol
Path	I-Protocol
First	I-Protocol
(	O
OSPF	B-Protocol
)	O
,	O
and	O
appear	O
as	O
a	O
router	O
to	O
the	O
rest	O
of	O
the	O
network	O
.	O
</s>
<s>
If	O
one	O
network	O
interface	O
fails	O
,	O
normal	O
OSPF	B-Protocol
topology	O
reconvergence	O
will	O
cause	O
traffic	O
to	O
be	O
sent	O
via	O
another	O
interface	O
.	O
</s>
<s>
A	O
VIP	B-Operating_System
address	I-Operating_System
can	O
be	O
used	O
to	O
provide	O
nearly	O
unlimited	O
mobility	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
an	O
application	O
has	O
an	O
IP	B-Protocol
address	I-Protocol
on	O
a	O
physical	O
subnet	O
,	O
that	O
application	O
can	O
be	O
moved	O
only	O
to	O
a	O
host	O
on	O
that	O
same	O
subnet	O
.	O
</s>
