Some older versions of BIND are limited to 22 characters.
At this point, this limititation should be around 64 characters per part
For example :
microsoft -> this is a part, can be 64 characters
com -> this is a part, can be 64 chars
Since the number of 'parts' if not really limited, I guess you can create very very large (sub)domain names... (untill the RAM of your server is filled with it... hehe)
I would advise to use a shorter filename than the lenght of your domain name
for example :
domain name :thisismydomainname.com
filename : thisis.com.dns
Hope this helps Peter Van Eeckhoutte
peter.ve@pandora.be