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• SOA — Start Of Authority resource record, proclaims important authoritative information abouta namespace to the nameserver.Located after the directives, an SOA resource record is the first resource record in a zone file.The following example shows the basic structure of an SOA resource record:@ IN SOA ()The @ symbol places the $ORIGIN directive (or the zone's name, if the $ORIGIN directive is notset) as the namespace being defined by this SOA resource record. The hostname of theprimary nameserver that is authoritative for this domain is the directive, and the email of the person to contact about this namespace is the directive.The directive is a numerical value incremented every time the zone file isaltered to indicate it is time for named to reload the zone. The directive isthe numerical value slave servers use to determine how long to wait before asking the masternameserver if any changes have been made to the zone. The directive is anumerical value used by the slave servers to determine if it is using outdated zone data andshould therefore refresh it.The directive is a numerical value used by slave servers to determine thelength of time to wait before issuing a refresh request in the event the master nameserver isnot answering. If the master has not replied to a refresh request before the amount of timespecified in the directive elapses, the slave servers stop responding asan authority for requests concerning that namespace.The directive is the quantity of time other nameservers cache the zone'sinformation.When configuring BIND, all times are specified in seconds. However, it is possible to useabbreviations when specifying units of time other than seconds, such as minutes (M), hours(H), days (D), and weeks (W). The table in Table 12.1, “Seconds compared to other time units”shows an amount of time in seconds and the equivalent time in another format.Seconds Other Time Units60 1M1800 30M3600 1H10800 3H21600 6H43200 12H86400 1DZone File Resource Records225 |
