<s>
A	O
start	B-Protocol
of	I-Protocol
authority	I-Protocol
record	O
(	O
abbreviated	O
as	O
SOA	B-Protocol
record	I-Protocol
)	O
is	O
a	O
type	O
of	O
resource	O
record	O
in	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
containing	O
administrative	O
information	O
about	O
the	O
zone	O
,	O
especially	O
regarding	O
zone	B-Protocol
transfers	I-Protocol
.	O
</s>
<s>
The	O
SOA	B-Protocol
record	I-Protocol
format	O
is	O
specified	O
in	O
RFC	O
1035	O
.	O
</s>
<s>
Normally	O
DNS	B-Protocol
name	I-Protocol
servers	O
are	O
set	O
up	O
in	O
clusters	O
.	O
</s>
<s>
The	O
database	O
within	O
each	O
cluster	O
is	O
synchronized	O
through	O
zone	B-Protocol
transfers	I-Protocol
.	O
</s>
<s>
The	O
SOA	B-Protocol
record	I-Protocol
for	O
a	O
zone	O
contains	O
data	O
to	O
control	O
the	O
zone	B-Protocol
transfer	I-Protocol
.	O
</s>
<s>
Usually	O
the	O
SOA	B-Protocol
record	I-Protocol
is	O
located	O
at	O
the	O
top	O
of	O
the	O
zone	O
.	O
</s>
<s>
A	O
zone	O
without	O
a	O
SOA	B-Protocol
record	I-Protocol
does	O
not	O
conform	O
to	O
the	O
standard	O
required	O
by	O
RFC1035	O
.	O
</s>
<s>
If	O
a	O
secondary	O
name	O
server	O
slaved	O
to	O
this	O
one	O
observes	O
an	O
increase	O
in	O
this	O
number	O
,	O
the	O
slave	O
will	O
assume	O
that	O
the	O
zone	O
has	O
been	O
updated	O
and	O
initiate	O
a	O
zone	B-Protocol
transfer	I-Protocol
.	O
</s>
<s>
REFRESH	O
Number	O
of	O
seconds	O
after	O
which	O
secondary	O
name	O
servers	O
should	O
query	O
the	O
master	O
for	O
the	O
SOA	B-Protocol
record	I-Protocol
,	O
to	O
detect	O
zone	O
changes	O
.	O
</s>
<s>
MINIMUM	O
Used	O
in	O
calculating	O
the	O
time	O
to	O
live	O
for	O
purposes	O
of	O
negative	B-Error_Name
caching	I-Error_Name
.	O
</s>
<s>
Sample	O
SOA	B-Protocol
record	I-Protocol
for	O
example.org,	O
in	O
BIND	B-Protocol
syntax	O
.	O
</s>
<s>
Several	O
methods	O
have	O
been	O
established	O
for	O
updates	O
to	O
the	O
SERIAL	O
field	O
of	O
a	O
zone	O
's	O
SOA	B-Protocol
record	I-Protocol
:	O
</s>
<s>
The	O
serial	O
number	O
is	O
the	O
time	O
of	O
last	O
modification	O
to	O
the	O
zone	O
's	O
data	O
file	O
expressed	O
as	O
the	O
number	O
of	O
seconds	O
since	O
the	O
UNIX	B-Operating_System
epoch	I-Operating_System
.	O
</s>
<s>
This	O
method	O
is	O
used	O
by	O
default	O
in	O
the	O
djbdns	B-Protocol
suite	O
.	O
</s>
<s>
Although	O
it	O
uses	O
a	O
32-bit	O
counter	O
,	O
it	O
is	O
not	O
susceptible	O
to	O
the	O
year	B-Application
2038	I-Application
problem	I-Application
due	O
to	O
the	O
effect	O
of	O
serial	B-Protocol
number	I-Protocol
arithmetic	I-Protocol
.	O
</s>
