<s>
A	O
care-of	B-Protocol
address	I-Protocol
(	O
usually	O
referred	O
to	O
as	O
CoA	O
)	O
is	O
a	O
temporary	O
IP	B-Protocol
address	I-Protocol
for	O
a	O
mobile	B-Application
device	I-Application
used	O
in	O
Internet	O
routing	O
.	O
</s>
<s>
This	O
allows	O
a	O
home	O
agent	O
to	O
forward	O
messages	O
to	O
the	O
mobile	B-Application
device	I-Application
.	O
</s>
<s>
A	O
separate	O
address	O
is	O
required	O
because	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
device	O
that	O
is	O
used	O
as	O
host	O
identification	O
is	O
topologically	O
incorrect	O
—	O
it	O
does	O
not	O
match	O
the	O
network	O
of	O
attachment	O
.	O
</s>
<s>
The	O
care-of	B-Protocol
address	I-Protocol
splits	O
the	O
dual	O
nature	O
of	O
an	O
IP	B-Protocol
address	I-Protocol
,	O
that	O
is	O
,	O
its	O
use	O
is	O
to	O
identify	O
the	O
host	O
and	O
the	O
location	O
within	O
the	O
global	O
IP	O
network	O
.	O
</s>
<s>
The	O
care-of	B-Protocol
address	I-Protocol
can	O
be	O
acquired	O
by	O
the	O
mobile	O
node	B-Protocol
in	O
two	O
different	O
ways	O
:	O
</s>
<s>
Foreign	O
agent	O
care-of	B-Protocol
address	I-Protocol
(	O
FACoA	O
)	O
:	O
The	O
mobile	O
node	B-Protocol
receives	O
the	O
same	O
CoA	O
as	O
the	O
foreign	O
agent	O
.	O
</s>
<s>
Co-located	O
care-of	B-Protocol
address	I-Protocol
:	O
Each	O
mobile	O
node	B-Protocol
in	O
the	O
foreign	O
network	O
is	O
assigned	O
its	O
own	O
CoA	O
,	O
usually	O
by	O
a	O
DHCP	B-Protocol
server	I-Protocol
.	O
</s>
<s>
Given	O
the	O
imminent	O
IPv4	B-Protocol
address	I-Protocol
exhaustion	I-Protocol
,	O
the	O
first	O
solution	O
is	O
more	O
frequently	O
chosen	O
,	O
because	O
it	O
does	O
not	O
waste	O
a	O
public	O
IP	B-Protocol
address	I-Protocol
for	O
every	O
mobile	O
node	B-Protocol
when	O
changing	O
network	O
location	O
,	O
as	O
the	O
collocated	O
CoA	O
does	O
.	O
</s>
<s>
The	O
care-of	B-Protocol
address	I-Protocol
has	O
to	O
be	O
a	O
valid	O
IP	B-Protocol
address	I-Protocol
within	O
the	O
foreign	O
network	O
,	O
so	O
that	O
it	O
allows	O
the	O
mobile	O
node	B-Protocol
to	O
receive	O
and	O
make	O
connections	O
with	O
any	O
host	O
in	O
the	O
outside	O
.	O
</s>
<s>
To	O
send	O
outgoing	O
packets	O
,	O
the	O
mobile	O
node	B-Protocol
may	O
as	O
well	O
use	O
its	O
home	O
address	O
but	O
,	O
since	O
it	O
is	O
not	O
a	O
connected	O
IP	B-Protocol
address	I-Protocol
for	O
the	O
current	O
network	O
attachment	O
,	O
some	O
routers	B-Protocol
in	O
the	O
way	O
might	O
prevent	O
the	O
packets	O
from	O
reaching	O
the	O
destination	O
.	O
</s>
<s>
That	O
is	O
why	O
,	O
in	O
IPv4	B-Protocol
,	O
the	O
outgoing	O
information	O
is	O
transported	O
to	O
the	O
home	O
agent	O
(	O
which	O
is	O
in	O
the	O
home	O
network	O
)	O
by	O
means	O
of	O
an	O
IP	B-Protocol
tunnel	I-Protocol
.	O
</s>
<s>
From	O
the	O
Home	O
Network	O
,	O
the	O
packets	O
of	O
the	O
Mobile	O
Node	B-Protocol
can	O
be	O
sent	O
using	O
its	O
original	O
Home	O
Address	O
,	O
without	O
any	O
routing	O
problem	O
.	O
</s>
<s>
The	O
Correspondent	O
Node	B-Protocol
will	O
send	O
its	O
information	O
again	O
to	O
the	O
Home	O
Network	O
.	O
</s>
<s>
Thus	O
,	O
it	O
has	O
to	O
be	O
sent	O
on	O
through	O
the	O
tunnel	O
to	O
the	O
foreign	O
agent	O
and	O
then	O
to	O
the	O
Mobile	O
Node	B-Protocol
.	O
</s>
<s>
When	O
all	O
mobile	O
nodes	O
share	O
the	O
same	O
IP	B-Protocol
address	I-Protocol
with	O
the	O
foreign	O
agent	O
,	O
this	O
is	O
implemented	O
by	O
the	O
foreign	O
agent	O
acting	O
as	O
a	O
proxy	B-Protocol
ARP	I-Protocol
.	O
</s>
