I have a domain "example.com" with subdomain "sub1.example.com" defined as an "A" record in the bind zone file.
How can I define something like "sub2.sub1.example.com"?
Simply, if your subdomain is like:
sub1 IN 1H A 192.168.1.1
sub2.sub1.example.com would be something like:
sub2.sub1 IN 1H A 192.168.1.2