IP check

["Simone Nanni" <simone.nanni () ptvonline it>]

Hi everybody!
I'm newbie in snort configuring (about 3 days........) and i have a question for you!
I have configured my snort-machine to analize only my internal lan traffic and i want to manage ip/mac couple for every 
host.
I explain it:
i want to register every ip/mac for every host and i want to be alerted if somebody changes his/her ip address or a new 
mac address appear on the network
(i.e. somebody attach his/her laptop on the lan without authorization)......
What i have to do???????

Thanx a lot in advance!
Simone Nanni.