Any tool or theorical method on detecting number of computer behind a NAT box?

hi, Sharing internet access bandwidth between multiple computers is common today. Usually, bandwidth sharer bought a little router with NAT/PAT function. After connecting that box to a ADSL/LAN access link, multiple computer could share a single access link. I heard some company provide prdouct for detecting number of computers behind NAT/PAT box. Is there any paper or document on how such product work? where could I fint them ? Joe ______________________________________________________________________ Search, browse and book your hotels and flights through Yahoo! Travel. http://sg.travel.yahoo.com