Newbie: in-addr.arpa file for a C Class

[belacyrf]

Can anyone point me in the right direction.  We have a couple reverse
files 3.2.1.rev for a few of our c classes.  In these files we specify
the individual reverse entries for each IP.

How do I set up a single in-addr.arpa entry for a full C Class.

For example.  I just want to set up an "in-addr.arpa" file for the
3.2.1 c class... I dont want to do it by IP.  If I'm not making sense,
I'm sorry, I'm pretty new. thanks