<s>
A	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
zone	B-Protocol
file	I-Protocol
is	O
a	O
text	B-General_Concept
file	I-General_Concept
that	O
describes	O
a	O
DNS	B-Protocol
zone	I-Protocol
.	O
</s>
<s>
A	O
DNS	B-Protocol
zone	I-Protocol
is	O
a	O
subset	O
,	O
often	O
a	O
single	O
domain	O
,	O
of	O
the	O
hierarchical	O
domain	O
name	O
structure	O
of	O
the	O
DNS	B-Protocol
.	O
</s>
<s>
The	O
zone	B-Protocol
file	I-Protocol
contains	O
mappings	O
between	O
domain	O
names	O
and	O
IP	B-Protocol
addresses	I-Protocol
and	O
other	O
resources	O
,	O
organized	O
in	O
the	O
form	O
of	O
text	O
representations	O
of	O
resource	O
records	O
(	O
RR	O
)	O
.	O
</s>
<s>
A	O
zone	B-Protocol
file	I-Protocol
may	O
be	O
either	O
a	O
DNS	B-Protocol
master	O
file	O
,	O
authoritatively	O
describing	O
a	O
zone	O
,	O
or	O
it	O
may	O
be	O
used	O
to	O
list	O
the	O
contents	O
of	O
a	O
DNS	B-Protocol
cache	O
.	O
</s>
<s>
The	O
format	O
of	O
a	O
zone	B-Protocol
file	I-Protocol
is	O
defined	O
in	O
(	O
section	O
5	O
)	O
and	O
(	O
section	O
3.6.1	O
)	O
.	O
</s>
<s>
This	O
format	O
was	O
originally	O
used	O
by	O
the	O
Berkeley	B-Protocol
Internet	I-Protocol
Name	I-Protocol
Domain	I-Protocol
(	O
BIND	B-Protocol
)	O
software	O
package	O
,	O
but	O
has	O
been	O
widely	O
adopted	O
by	O
other	O
DNS	B-Protocol
server	I-Protocol
software	O
–	O
though	O
some	O
of	O
them	O
(	O
e.g.	O
</s>
<s>
NSD	B-Protocol
,	O
PowerDNS	B-Language
)	O
are	O
using	O
the	O
zone	B-Protocol
files	I-Protocol
only	O
as	O
a	O
starting	O
point	O
to	O
compile	O
them	O
into	O
database	O
format	O
,	O
see	O
also	O
Microsoft	B-Protocol
DNS	I-Protocol
with	O
Active	O
Directory-database	O
integration	O
.	O
</s>
<s>
A	O
zone	B-Protocol
file	I-Protocol
is	O
a	O
sequence	O
of	O
line-oriented	O
entries	O
,	O
each	O
of	O
which	O
is	O
either	O
a	O
directive	O
or	O
a	O
text	O
description	O
that	O
defines	O
a	O
single	O
resource	O
record	O
(	O
RR	O
)	O
.	O
</s>
<s>
Entries	O
may	O
occur	O
in	O
any	O
order	O
in	O
a	O
zone	B-Protocol
file	I-Protocol
,	O
with	O
some	O
exceptions	O
.	O
</s>
<s>
Directives	O
are	O
control	O
entries	O
that	O
affect	O
the	O
rest	O
of	O
the	O
zone	B-Protocol
file	I-Protocol
.	O
</s>
<s>
$GENERATE	O
,	O
a	O
non-standard	O
extension	O
accepted	O
by	O
BIND	B-Protocol
and	O
some	O
other	O
name	B-Protocol
server	I-Protocol
software	O
to	O
insert	O
multiple	O
resource	O
records	O
with	O
one	O
entry	O
,	O
is	O
followed	O
by	O
a	O
concise	O
representation	O
of	O
an	O
increasing	O
sequence	O
of	O
nonnegative	O
numbers	O
and	O
then	O
a	O
template	O
RR	O
entry	O
.	O
</s>
<s>
Some	O
name	B-Protocol
servers	I-Protocol
,	O
including	O
BIND	B-Protocol
,	O
allow	O
nonstandard	O
representations	O
that	O
use	O
time	O
unit	O
abbreviations	O
(	O
for	O
example	O
,	O
"	O
2d	O
"	O
meaning	O
two	O
24-hour	O
days	O
or	O
"	O
1h30m	O
"	O
meaning	O
one	O
hour	O
and	O
30	O
minutes	O
)	O
.	O
</s>
<s>
The	O
most	O
commonly	O
used	O
namespace	O
is	O
that	O
of	O
the	O
Internet	O
,	O
indicated	O
by	O
parameter	O
IN	O
,	O
but	O
others	O
exist	O
and	O
are	O
in	O
use	O
,	O
e.g.	O
,	O
CHAOS	B-General_Concept
.	O
</s>
<s>
For	O
example	O
:	O
an	O
address	O
record	O
(	O
type	O
A	O
for	O
IPv4	O
,	O
or	O
type	O
AAAA	O
for	O
IPv6	O
,	O
)	O
maps	O
the	O
domain	O
name	O
from	O
the	O
first	O
field	O
to	O
an	O
IP	B-Protocol
address	I-Protocol
in	O
the	O
record	O
data	O
;	O
a	O
mail	O
exchanger	O
record	O
(	O
type	O
MX	O
)	O
specifies	O
the	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
mail	O
host	O
for	O
a	O
domain	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
zone	B-Protocol
file	I-Protocol
for	O
the	O
domain	O
example.com	O
is	O
the	O
following	O
:	O
</s>
<s>
At	O
minimum	O
,	O
the	O
zone	B-Protocol
file	I-Protocol
must	O
specify	O
the	O
Start	O
of	O
Authority	O
(	O
SOA	O
)	O
record	O
with	O
the	O
name	O
of	O
the	O
authoritative	O
master	O
name	B-Protocol
server	I-Protocol
for	O
the	O
zone	O
and	O
the	O
email	O
address	O
of	O
someone	O
responsible	O
for	O
management	O
of	O
the	O
name	B-Protocol
server	I-Protocol
(	O
represented	O
as	O
a	O
domain	O
name	O
,	O
with	O
a	O
full	O
stop	O
character	O
in	O
place	O
of	O
the	O
usual	O
@	O
symbol	O
)	O
.	O
</s>
<s>
Some	O
name	B-Protocol
servers	I-Protocol
,	O
including	O
BIND	B-Protocol
,	O
also	O
require	O
at	O
least	O
one	O
additional	O
NS	O
record	O
.	O
</s>
<s>
In	O
the	O
zone	B-Protocol
file	I-Protocol
,	O
domain	O
names	O
that	O
end	O
with	O
a	O
full	O
stop	O
character	O
(	O
such	O
as	O
"	O
example.com	O
.	O
"	O
</s>
<s>
in	O
the	O
above	O
example	O
)	O
are	O
fully	B-Protocol
qualified	I-Protocol
while	O
those	O
that	O
do	O
not	O
end	O
with	O
a	O
full	O
stop	O
are	O
relative	O
to	O
the	O
current	O
origin	O
(	O
which	O
is	O
why	O
www	O
in	O
the	O
above	O
example	O
refers	O
to	O
www.example.com	O
)	O
.	O
</s>
<s>
A	O
zone	B-Protocol
file	I-Protocol
is	O
referenced	O
by	O
the	O
configuration	O
file	O
of	O
the	O
name	B-Protocol
server	I-Protocol
software	O
.	O
</s>
<s>
For	O
example	O
,	O
BIND	B-Protocol
typically	O
uses	O
a	O
statement	O
such	O
as	O
:	O
</s>
<s>
The	O
zone	B-Protocol
files	I-Protocol
for	O
the	O
DNS	B-Protocol
root	I-Protocol
zone	I-Protocol
and	O
for	O
the	O
set	O
of	O
top-level	O
domains	O
contain	O
resource	O
records	O
only	O
for	O
the	O
authoritative	O
domain	B-Protocol
name	I-Protocol
servers	I-Protocol
for	O
each	O
domain	O
name	O
.	O
</s>
<s>
Some	O
server	O
software	O
automatically	O
configures	O
resource	O
records	O
for	O
specially	O
recognized	O
domains	O
or	O
hostnames	O
,	O
such	O
as	O
localhost	B-Protocol
,	O
but	O
a	O
customized	O
zone	O
master	O
file	O
may	O
be	O
used	O
.	O
</s>
<s>
An	O
example	O
for	O
manual	O
configuration	O
of	O
the	O
forward	O
zone	O
for	O
localhost	B-Protocol
is	O
the	O
following	O
:	O
</s>
<s>
Such	O
zone	B-Protocol
files	I-Protocol
prevent	O
a	O
DNS	B-Protocol
server	I-Protocol
from	O
referring	O
to	O
other	O
,	O
possibly	O
external	O
DNS	B-Protocol
servers	I-Protocol
.	O
</s>
