[Samba] domain question

[Jon Reynolds]

I am playing around with using samba as a domain controller and have a
question. If I setup a domain how do I make it so that my servers are
only accessible if they logon on to the domain? This is the scenario
that I am thinking about.

I have a win9*/2000/XP system that I connect to the LAN, I cannot log on
to the domain because I don't have an account. I find the IP of a file
server on the network and begin to try and gain access by using
username/password combo's. How do I prevent this scenario from
happening?

I am sure the answer is obvious but I don't know what I am looking for.
Could someone give me a clue as to what I will need to do?

Thanks for any help,

Jon