Scanning that network

Some options: There is the master of all network scanner: Nmap and its Front end ZenMap (downloaded in the same package) Of which Hak5 has done a lovely little series on using. but it aint pretty, and often feels like hunting mosquitoes with a howitzer. I will admit this, with time and effort you will get more specific and more useful information from Nmap than most other free tools. However for your first review of your environment, it will create more confusion than clarity. If your on a windows machine, there is an old but excellent sysinternals (hey, go with people you trust, and you cant get much more trustworthy than them) tool called ShareEnum which is part of the SysinternalSuite. Its starting to show its age, but its still solid(interestingly, MS says the suite was updated on 9-11-14, but this specific tools was not). It will give you the machines, shares, IPs, some ports and SNMP responses for a list of community strings. Speaking of SNMP scanning, McAfee (I know, I know, but its a scan tool, not an antivirus machine killing pile of wonderfulness) makes a free and useful if clunky looking SNMP scanning tool called SNScan.exe which is pretty fast but really a one trick pony. For full network inventory, including users on your AD, machines and switches, you can use something like spiceworks or lansweeper. Both are free, but spiceworks is unlimited free use, lansweeper costs money after the first 100 "assets". As management tools go, its inexpensive, but Im not certain its worth even that cost when compared with spiceworks or a more expensive solution. The downside to spiceworks of course is dealing with the constant marketing, but that's how they pay for the service and software you get. Between these items, and the AngryIP Scanner I talked about earlier, you can get a good basic scan going. Of note, Lansweeper and Spiceworks will help you keep track of the scan results over time. The rest that I mentioned (well..... nmap....but.....) not so much. However, making sense of that data on round one, not always so easy.