How to apply DNS to my environment?

[Bruce Ordway]

Hi,

I've been fooling around with sendmail & a couple of servers for a while.
After getting some advice from a sendmail newsgroup it seems that I really
need to figure out my DNS first. I've been reading a lot but I am not
digesting too well yet. Let me explain my layout & then please, if you have
any advice, it is welcome.

I have an NT4 server, WINS no DNS & the "domain" is VIKING. All of my
clients are WinXX & they logon to the NT4 VIKING domain. We use TCP/IP and
our addresses are 128.1.1.xxx. We don't have a legal domain name.

I have a RH6.1 Linux server running ipchains that acts as the internet
gateway for my MS clients. I don't have a static IP address or a "real"
domain name. I have not done any DNS configuration yet. When I check
sendmail I see the following values:
short domain name = localhost
canonical domain name = localhost.localdomain
subdomain name = localdomain
node name = Proxy01

I also have an HPUX database server. I have not done any DNS configuration
here either. When I check sendmail I see the following values:
short domain name = hpk100
canonical domain name = hpk100
subdomain name = <null>
node name = hpk100

So the NT & HPUX systems have been set up as stand alone units not connected
to the Internet. The Linux box was installed to handle IP masquerading & get
around our illegal IP addresses.
How do I know if DNS is running on a Linux or HPUX system?
How do I implement DNS into a private network with illegal this?
Can this screw up ipchains on the Linux box?
Can I screw things up on the Internet?

Thanks,
Bruce Ordway