This code utilizes the p0f derived OS signature database of disco to actively fingerprint operating systems. It is able to fingerprint hosts based on a single SYN-ACK received from a probed port, and as such can be used to identify multiple hosts NAT Masquerading behind a single IP.
You can download it from the following link: https://packetstormsecurity.com/files/download/67115/inth-v0.2.tgz
Source: https://packetstormsecurity.com/files/67115/inth-v0.2.tgz.html