DNS and domains

[levartze]

I setup a system about 10 yrs ago with an inside (private) network and an 
outside (public) network and a firewall in between using bind4.  The inside 
and outside used the same domain with different IP's and neither could see 
the other because of the firewall.  I firewall has a pool of valid IP for 
NAT for those external requests from the inside.  At that time the network 
was quite small and since then has grown substantially (1500+ nodes).

I would like to try and change the inside network domain to a different one 
(i.e. change it from mydomain.net to mydomain.lan).  This way seems much 
cleaner and I'm trying to install a new nameserver with bind9, so the timing 
would be right for doing this.

Also, I have several subnets (i.e., 10.1.0.0/24, 
10.2.0.0/24,10.3.0.0/24,...).
Should I have a separate sub-domain for each of these ?
(i.e. subnet_10_1.lan, subnet_10_2.lan, subnet_10_3.lan,...)

Is there any reference material dealing with kind of thing that someone 
could recommend?

Any suggestions would be greatly appreciated.

Thank you,

Bob