Red Hat ENTERPRISE LINUX 3 Reference Manual page 209

Chapter 12. Berkeley Internet Name Domain (BIND)
The symbol places the
@
set) as the namespace being defined by this
nameserver that is authoritative for this domain is the
and the email of the person to contact about this namespace is the
directive.
The
serial-number
altered to indicate it is time for
is the numerical value slave servers use to determine how long to wait before asking the master
nameserver if any changes have been made to the zone. The
numerical value used by the slave servers to determine if it is using outdated zone data and should
therefore refresh it.
The
time-to-retry
length of time to wait before issuing a refresh request in the event the master nameserver is not
answering. If the master has not replied to a refresh request before the amount of time specified in
the time-to-expire directive elapses, the slave servers stop responding as an authority for
requests concerning that namespace.
The minimum-TTL directive is the quantity of time other nameservers cache the zone's infor-
mation.
When configuring BIND, all times are specified in seconds. However, it is possible to use abbrevi-
ations when specifying units of time other than seconds, such as minutes (
and weeks ( ). The table in Table 12-1 shows an amount of time in seconds and the equivalent time
W
in another format.
Seconds
60
1800
3600
10800
21600
43200
86400
259200
604800
31536000
Table 12-1. Seconds compared to other time units
The following example illustrates the form an
with real values.
@ IN SOA
directive (or the zone's name, if the
$ORIGIN
directive is a numerical value incremented every time the zone file is
to reload the zone. The
named
directive is a numerical value used by slave servers to determine the
dns1.example.com.
2001062501 ; serial
21600 ; refresh after 6 hours
3600 ; retry after 1 hour
604800 ; expire after 1 week
86400 ) ; minimum TTL of 1 day
resource record. The hostname of the primary
SOA
primary-name-server
time-to-refresh directive
serial-number
Other Time Units
1M
30M
1H
3H
6H
12H
1D
3D
1W
365D
resource record might take when it is populated
SOA
hostmaster.example.com. (
directive is not
$ORIGIN
directive,
hostmaster-email
directive is a
), hours ( ), days (
M H
191
),
D