How should I configure internal and external DNS servers

[Nick Howitt]

Hi,

I am fairly new to bind but I am thinking my company's use of it is 
sub-optimal. We have two bind masters (and a few slaves), one for 
internal use so all our internal servers point to it or its slaves as 
their DNS resolvers. I will call the internal one bind-internal and the 
external one bind-external.

Bind-internal is set up as authoritative for the domain example.com.
Bind-external is also set up as authoritative for example.com.

Bind-internal has all sorts of entries resolving in the 10.30, 10.40 and 
other private ranges, but it also has entries resolving to our public 
IP's e.g. demo.example.com resolves to 1.2.3.4 (terminated by an F5), 
which is one of our public ips (munged). As this site is externally 
accessible as well, we also have to put an identical entry in 
bind-external so we end up having many identical entries in 
bind-internal and bind-external. We also have some other domains covered 
by bind-internal with external IPs, but externally they are covered by 
the domain host's DNS and they have the same issue where in 
bind-internal we have some public IP's which are also in the domain 
host's DNS for external access.

I have a feeling this is a sub-optimal setup, having to maintain 
external IPs in both bind-internal and bind-external. Does it make sense 
to stop bind-internal from being authoritative and make it a 
resolver/caching name server? This way, if it does not find an entry in 
bind-internal it will then go out to either bind-external or the domain 
host's DNS to get the answer from the authoritative servers and then 
there is no need to maintain external IPs in bind internal.

TIA,

Nick