Other Os Detection Techniques are based on analysing:
Running services; Open port patterns. Limitations
Many passive fingerprinters are getting confused when analysing packets from a NAT device.
Os Detection Techniques – IP TTL values + TCP Window size
Certain parameters within the TCP protocol definition are left up to the implementation. Different operating systems, and different versions of the same operating system, set different defaults for these values. By collecting and examining these values, one may differentiate among various operating systems, and implementations of TCP/IP. The TCP/IP fields that may vary include the following: