How do I build an asset inventory from network traffic?
Watch the network for a while and record every device that sends traffic, with the names it announces, its address and whom it talks to. Devices reveal themselves when they ask for an address (DHCP), resolve names (DNS), announce themselves on the local network, or connect to servers. A sensor on a mirror port collects this passively, without scanning anything, which matters for fragile devices such as printers, cameras and machines. Compare the result with the list you think you have: unknown devices, forgotten servers and personal equipment usually appear in the first days. Then give each device an owner and decide whether it belongs. NetSenX keeps a network map on every plan, Free included: devices seen on the LAN, their announced names, first and last seen, and who talks to whom. It only sees segments you monitor, and a device that never sends traffic does not appear.