I tested if it is possible to define a zone and a subzone FRED. In my
case a zone cr and a subzone ac.cr.
You can do that in this way:
1. Create the domain with a certain zone number, say 4 in our example.
The subzone is created, say, with number 5. That is, 4=cr. 5=ac.cr. You
must define records in the tables zone, zone_soa and zone_ns.
2. Define stanzas for both in the genzone.conf file.
After this you can generate independent zone files for the zone and the
subzone, say db.cr and db.ac.cr.
I hope this is useful.
Mario