Inventory of large networks

A good tips on how to make an inverntory of a large network is found on Link Using the free tool p0f connected to network span ports at central points, should give you quite good insight in the network traffic, without needing credentials.

P0f is a tool that utilizes an array of sophisticated, purely passive traffic fingerprinting mechanisms to identify the players behind any incidental TCP/IP communications (often as little as a single normal SYN) without interfering in any way.

p03 can be found here. If you need a precompiled version for windows, it can be found here.

A challenge would be to visualize the traffic. It would be interesting testing this a s a source for the HP uCMDB.