Split Namespace question.

[Cinense, Mark]

I will be using Bind9, and would like to implement a split namespace on the
current environment.  In reading the DNS & Bind 4th edition, it talks about
a bastion host.  In my environment, I have internal and external
nameservers, but no bastion host.  In order to do a split namespace is a
bastion host required?  If not, how could I do this with only internal and
external nameservers, and how does the zonefiles work, will I need to create
a separate zonefile for internal and external zones.  One other question is
how does the nameserver know what information do give and to whom, I know
you setup ACL's, but how does that work.

Thanks,

Mark