nmap is an amazing utility. With all of it’s flags and options it really gives you the power to know what is out in a network.

I used this to do a simple ping scan of my home network:

# nmap -nsP 192.168.1.0/24
Starting Nmap 5.00 ( http://nmap.org ) at 2013-08-22 09:06 MST
Host 192.168.1.1 is up (0.0051s latency).
MAC Address: 00:18:39:4E:82:60 (Cisco-Linksys)
Host 192.168.1.90 is up.
Nmap done: 256 IP addresses (2 hosts up) scanned in 5.51 seconds
#

Hosts that allow icmp echo requests will show up. I can see my router and my workstation, but no other hosts (no other pingable hosts at least). I’m looking for a RPi that I recently plugged into the network. It doesn’t look like it’s up. Time to drag out the spare monitor and keyboard…