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

THere was a paper of mine from a few years ago:
http://www.cs.columbia.edu/~smb/papers/fnat.pdf

    --Steve Bellovin, http://www.cs.columbia.edu/~smb