DNS zone file example

$TTL    86400
@       IN      SOA     ilab.cs.uoregon.edu. hostmaster.ilab.cs.uoregon.edu. (
                     2005070800         ; Serial
                          28800         ; Refresh
                           7200         ; Retry
                         604800         ; Expire
                          86400 )       ; Negative Cache TTL
;
@       IN      NS      ilab2.ilab.cs.uoregon.edu.
        IN      NS      dns.cs.uoregon.edu.
        IN      NS      phloem.uoregon.edu.
        IN      MX      0 ilab2.ilab.cs.uoregon.edu.

ilab-gw         IN      A       128.223.203.1
ilab2           IN      A       128.223.203.2
www             IN      CNAME   ilab2

$TTL 86400 defines a default TTL for records specified.

@ is a shorthand for the zone origin (here ilab.cs.uoregon.edu as defined in named.conf).

The SOA record contains several global parameters relating to the zone:

• the name of the zone
• a contact address for the zone (since @ cannot be used in the field, conventionally the @ in the email address is replaced with a .)
• a serial number which must be updated with each change to the zone data, which secondaries use to determine whether they need to retransfer the changed data. It is conventional to use a serial number of the format YYYYMMDDNN, which encodes the current date in Y/M/D format and an edit number in case you need to modify the file more than once in the same day.
• global timeout parameters for use by the secondaries, controlling how often they check for updates, retry oon failure, etc. These are recommended defaults.

Note that the ilab.cs.uoregon.edu domain name has some records associated with it besides the SOA, and additional subdomain records are also specified. In particular a zone origin must have a set of NS records, and these NS records must agree with the set of available servers that were delegated to the zone origin.

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