reverse cidr zones

[Jeff Stevens]

If I have a CIDR subnet from 192-255 (in zone 12.145.185), how is the zone 
defined such that we are authoritative only for that 192-255 range and not 
the entire 12.145.185 range?

I currently have a 185.145.12.in-addr.arpa zone with aliases that point to a 
192-255.185.145.12.in-addr.arpa. zone that has the actual PTRs.  However, I 
am unsure how to prevent our DNS from responding as authoritative for the 
range 0-191.185.145.12.in-addr.arpa.?

-- 
Jeffrey Stevens