<s>
The	O
Internet	B-Protocol
Protocol	I-Protocol
Version	I-Protocol
4	I-Protocol
address	O
can	O
have	O
multiple	O
uses	O
.	O
</s>
<s>
It	O
prohibits	O
this	O
as	O
a	O
destination	O
address	O
in	O
IPv4	B-Protocol
and	O
only	O
allows	O
it	O
as	O
a	O
source	O
address	O
under	O
specific	O
circumstances	O
.	O
</s>
<s>
Such	O
as	O
when	O
sending	O
the	O
initial	O
DHCPDISCOVER	O
packet	O
when	O
using	O
DHCP	B-Protocol
.	O
</s>
<s>
These	O
uses	O
do	O
not	O
result	O
in	O
IPv4	B-Protocol
packets	O
containing	O
and	O
so	O
are	O
not	O
necessarily	O
governed	O
by	O
RFC	O
1122	O
.	O
</s>
<s>
In	O
Linux	O
a	O
program	O
may	O
specify	O
as	O
the	O
remote	O
address	O
to	O
connect	O
to	O
the	O
current	O
host	O
(	O
AKA	O
localhost	B-Protocol
)	O
.	O
</s>
<s>
The	O
address	O
a	O
host	O
assigns	O
to	O
itself	O
when	O
address	O
request	O
via	O
DHCP	B-Protocol
has	O
failed	O
,	O
provided	O
the	O
host	O
's	O
IP	O
stack	O
supports	O
this	O
.	O
</s>
<s>
This	O
usage	O
has	O
been	O
replaced	O
with	O
the	O
APIPA	B-Protocol
mechanism	O
in	O
modern	O
operating	O
systems	O
.	O
</s>
<s>
For	O
example	O
use	O
in	O
DNS	O
can	O
cause	O
Linux	O
to	O
connect	O
to	O
Localhost	B-Protocol
instead	O
of	O
nothing	O
at	O
all	O
.	O
</s>
<s>
This	O
indicates	O
that	O
the	O
gateway	O
to	O
reach	O
the	O
corresponding	O
destination	O
subnet	B-Protocol
is	O
unspecified	O
.	O
</s>
<s>
This	O
should	O
not	O
be	O
confused	O
with	O
the	O
CIDR	B-Protocol
notation	I-Protocol
which	O
defines	O
an	O
IP	O
block	O
containing	O
all	O
possible	O
IP	O
addresses	O
.	O
</s>
<s>
It	O
is	O
commonly	O
used	O
in	O
routing	O
to	O
depict	O
the	O
default	B-Protocol
route	I-Protocol
as	O
a	O
destination	O
subnet	B-Protocol
.	O
</s>
<s>
It	O
matches	O
all	O
addresses	O
in	O
the	O
IPv4	B-Protocol
address	O
space	O
and	O
is	O
present	O
on	O
most	O
hosts	O
,	O
directed	O
towards	O
a	O
local	O
router	O
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
the	O
all-zeros	O
address	O
is	O
typically	O
represented	O
by	O
(	O
two	O
colons	O
)	O
,	O
which	O
is	O
the	O
short	O
notation	O
of	O
.	O
</s>
<s>
The	O
IPv6	B-Protocol
variant	O
serves	O
the	O
same	O
purpose	O
as	O
its	O
IPv4	B-Protocol
counterpart	O
.	O
</s>
