Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION, Руководство по развертыванию

Страница: 241 / 848

Zone File Resource Records
215
@ IN SOA <primary-name-server>
<hostmaster-email> (
<serial-number>
<time-to-refresh>
<time-to-retry>
<time-to-expire>
<minimum-TTL> )
The
@
symbol places the
$ORIGIN
directive (or the zone's name, if the
$ORIGIN
directive is not
set) as the namespace being defined by this
SOA
resource record. The hostname of the primary
nameserver that is authoritative for this domain is the
<primary-name-server>
directive, and
the email of the person to contact about this namespace is the
<hostmaster-email>
directive.
The
<serial-number>
directive is a numerical value incremented every time the zone file is
altered to indicate it is time for
named
to reload the zone. The
<time-to-refresh>
directive
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
<serial-number>
directive is
a numerical value used by the slave servers to determine if it is using outdated zone data and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>
directive is a numerical value used by slave servers to determine the
length of time to wait before issuing a refresh request in the event that 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.
In BIND 4 and 8, the
<minimum-TTL>
directive is the amount of time other nameservers cache
the zone's information. However, in BIND 9, the
<minimum-TTL>
directive defines how long
negative answers are cached for. Caching of negative answers can be set to a maximum of 3
hours (
3H
).
When configuring BIND, all times are specified in seconds. However, it is possible to use
abbreviations when specifying units of time other than seconds, such as minutes (
M
), hours (
H
),
days (
D
), and weeks (
W
). The table in
Table 17.1, “Seconds compared to other time units”
shows
an amount of time in seconds and the equivalent time in another format.
Seconds Other Time Units
60 1M
1800 30M
3600 1H
10800 3H
21600 6H
43200 12H
86400 1D
259200 3D
604800 1W
31536000 365D
Table 17.1. Seconds compared to other time units