The line in the boot file that designates the server as a primary master server for a zone looks as follows:
primary Berkeley.Edu ucbhosts
The first field specifies that the server is a primary one for the zone stated in the second field. The third field is the name of the file from which the data is read.
The above assumes that the zone you are specifying is a class IN zone. If you wish to designate a different class you can append /class to the first field, where class is either the integer value or the standard mnemonic for the class. For example the line for a primary server for a hesiod class zone looks as follows:
primary/HS Berkeley.Edu hesiod.data
Note that this support for specifying other than class IN zones is a compile-time option which your vendor may not have enabled when they built your operating system.