Operation Manual

a second time. Alternatively, @ can be entered here, in which case the zone
would be extracted 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. Be-
cause the @ sign already has a special meaning, "." is entered here instead.
For [e-mail] 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 le
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 species the time interval at which the secondary name
servers verify the zone serial number. In this case, one day.
Line 5:
The retry rate species the time interval at which a secondary name server,
in case of error, attempts to contact the primary server again. Here, two hours.
Line 6:
The expiration time species the time frame after which a secondary name
server discards the cached data if it has not regained contact to the primary server.
Here, a week.
Line 7:
The last entry in the SOA record species the negative caching TTL—the
time for which results of unresolved DNS queries from other servers may be cached.
306 Reference