Information Technology Reference
In-Depth Information
The SOA record is found in every zone and contains information that identifies the server pri-
marily responsible for the zone as well as some operational properties for the zone. Shown in
Figure 9-12, the SOA record contains the following information:
•
Serial number
—A revision number that increases each time data in the zone changes. This
number is used to determine when zone information should be replicated.
•
Primary server
—On a primary Active Directory-integrated zone, this field displays the
name of the server where DNS Manager is currently running. For a standard zone, it dis-
plays the primary DNS server's name.
•
Responsible person
—The e-mail address of the person responsible for managing the zone.
A period rather than an @ sign is used to separate the username from the domain name
(according to RFC 1183, which defines DNS resource record types).
•
Refresh interval
—Specifies how often a secondary DNS server attempts to renew its zone
information. When the interval expires, the server requests the SOA record from the pri-
mary DNS server. The serial number in the retrieved SOA record is then compared with the
serial number in the secondary server's SOA record. If the serial number has changed, the
secondary server requests a new copy of the zone data. After the transfer is completed,
the refresh interval begins anew. The default value is 15 minutes.
•
Retry interval
—The amount of time a secondary server waits before retrying a zone
transfer that has failed. This value should be less than the refresh interval and defaults
to 10 minutes. The retry interval begins after the refresh interval expires, and the pri-
mary server can't be contacted or the zone transfer fails.
•
Expires after
—The amount of time before a secondary server considers its zone data obsolete
if it can't contact the primary DNS server. If the refresh interval expires without a successful
zone transfer, this timer begins. If it expires without an update to the zone data (or an indica-
tion that the zone data hasn't changed), the DNS server stops responding to queries. This
value must be higher than the refresh and retry intervals combined; the default is 1 day.
9
Figure 9-12
SOA record information
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