[CentOS] stupid Centos-DS questions

OK, I'm mostly through everything up to and including Chapter 5 in
http://www.redhat.com/docs/manuals/dir-server/8.1/install/Installation_Guide-Advanced_Configuration-Making-DS.html

And looking through the ToC for the rest, I do not see that my
questions will be answered by this doc.  So please feel free to point
me to other docs.

This manual seems to assuming I already know what it is I want to do,
and what "Directory Services" are all about.   Invalid assumption.

For example, right now I am reading about how to set up different
instances of this-or-that (Admin Server, Directory Server, yadda,
yadda).   What it does not tell me is why I would want to do that.  It
does not even tell me "what is an 'instance'" .

I've never done any sort of DS, so this is all new stuff to me.
Suggested reading is very welcomed.

What is even more welcome is pointers to case studies or template
examples.   We are a very small company with only about 30 people
right now.  Though we do have a convoluted network with 3 distinct
network areas separated by VPNs.  I'm new here (and put in charge),
and we are not even running DNS yet (eeep!  for REALZ!!!).   To me it
makes sense to have 3 different DNS subdomains because of some quirks
they have in their product architecture here.   I'm thinking
"office.example.dom", "production.example.com" and "rc.example.com".
And from the bit I've read so far on DS, it seems to be recommended to
have your DS mirror your DNS.   So we are small enough where I do not
think we need more than 1 server to run it all.  And I can make all
the machines talk to that server through the firewalls separating the
3 zones.  That is not an issue at all.   I'm not sure how this affects
my DS.   Would these be "instances"?

So many questions ... please suggest reading material.

thanks,
-Alan

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