34. How can I control which clients get leases from my server?
There is no ideal answer: you have to give something up or do some extra work.
You can put all your clients on a subnet of your own along with your own DHCP server.
You can use manual allocation.
Perhaps you can find DHCP server software that allows you to list which MAC addresses the server will accept. DHCP servers that support roaming machines may be adapted to such use.
You can use the user class option assuming your clients and server support it: it will require you to configure each of your clients with a user class name. You still depend upon the other clients to respect your wishes.
35. How can I prevent unauthorized laptops from using a network that uses DHCP for dynamic addressing?
This would have to be done using a mechanism other than DHCP. DHCP does not prevent other clients from using the addresses it is set to hand out nor can it distinguish between a computer’s permanent MAC address and one set by the computer’s user. DHCP can impose no restrictions on what IP address can use a particular port nor control the IP address used by any client.