Dear brian and zaco, thank you very much for your reply. Here, in this apartement where I am working now has been already set-up network. Then, the bos asked me to write code which will assign ip address into internet users each time they get connected to the network. And this ip addresses are specific into certain rooms. For example, room 1 has ip address bla.bla.bla.bla. I don't know how to solve this problem with perl. I am new into this what many people call as mighty programming language. But, I just figured out, that I can write a web interface in which users will input their username and password, and then their computers will be assigned with ip addresses which have been decided to be used in their room by a little perl CGI script. The scheme is username:password:ip-address. My bos only wants every rooms has their own ip address. Then, my bos able to monitor the access of the internet for each room. Because if each room has its own ip address, then we will know what's room which has a given ip address. This kind of thing can not be implemented in DHCP. So, this is the problem exactly. Thank you very much again for your help. It's very much useful for newbie just like me.