Novell LINUX ENTERPRISE SERVER 11 - ADMINISTRATION Administration Manual page 311

Line 1:
$TTL defines the default time to live that should apply to all the entries in this file.
In this example, entries are valid for a period of two days (2 D).
Line 2:
This is where the SOA (start of authority) control record begins:
• The name of the domain to administer is example.com in the first position.
This ends with ".", because otherwise the zone would be appended a second
time. Alternatively, @ can be entered here, in which case the zone would be ex-
tracted from the corresponding entry in /etc/named.conf.
• After IN SOA is the name of the name server in charge as master for this zone.
The name is expanded from dns to dns.example.com, because it does not
end with a ".".
• An e-mail address of the person in charge of this name server follows. Because
the @ sign already has a special meaning, "." is entered here instead. For
root@example.com the entry must read root.example.com.. The "."
must be included at the end to prevent the zone from being added.
• The ( includes all lines up to ) into the SOA record.
Line 3:
The serial number is an arbitrary number that is increased each time this file
is changed. It is needed to inform the secondary name servers (slave servers) of
changes. For this, a 10 digit number of the date and run number, written as
YYYYMMDDNN, has become the customary format.
Line 4:
The refresh rate specifies the time interval at which the secondary name
servers verify the zone serial number. In this case, one day.
Line 5:
The retry rate specifies the time interval at which a secondary name server,
in case of error, attempts to contact the primary server again. Here, two hours.
The Domain Name System 297