ip secure distribution

dear sir :
this is ghassan chehade

i have a multi lan & wan : 192.168.27.x
192.168.28.x and so on
where x is from 1 to 254 with excluding values for future use.
i mean my distribution is: 192.168.27.1
192.168.27.2 …
192.168.27.(3-100) reserve
and so on.
so my question : how can i stopped any new ip from somebody.
i need a program which generates many ip addresses
for dummy ..
for that any new user need a permission or a specified ip to enter the network
thks
sorry