How are clients in an Leopard Client/Server verified in Kerberos before they join?

Hi !
I have some Leopard Clients (6 at the moment) and a Leopard Server. I want the clients to get the homedirs and authentication for the users from the server using Network Home Folders and OpenDirectory, since this seems to be the best way. Our network is not completly closed however, there are other departments in our subnet and users can use wall-mounted ports to access the network in general. The problem is, I am not sure how/if not-authorized clients can join the Kerberos realm and get user information from the server, for example. Is there a way to bind specific clients to the server and vice versa? 😯