I’m starting to administer a small but confusing und badly documented local heterogeneous network (mostly Windows workstations, printers, laboratory equipment, etc. and one Linux/Samba Server) (192.168.1.0/24) stretching over a few hundred m2 office and factory area in two floors. In principle I have access to all the passwords and rooms. In praxis some of the offices are locked, the owners are out and there might be some hidden devices which somebody who is not reachable for me has connected to the LAN or which were plugged in and forgotten at all.
When configuring printers (we have quite a lot of them) I sometimes get a collision warning. Most devices get their IPs via DHCP, but not all of them. Some of the devices use firewalls which block ports and or do not answer pings for other reasons.
I want to scan the network for used IPs - just now manually, later perhaps a few times automatically to also catch fixed IP devices which were switched off during the first scan.
What is the best method to perform such a scan, and what tool should I use? As the budget is limited and this task probably needs not to be done on a regular basis I would prefer a free open source solution.