I’m a huge fan of a tool called nmap (nmap.org). It is a network tool that can do many things. The most simple is to determine if a host is active. Anytime I connect to any network I run a quick scan to see who my neighbors are on the network.
To do a network scan with nmap you only need one bit of information. Your IP address. Below is a scan from my local network. I was able to do a quick ipconfig to see my local IP was (192.168.2.118) armed with that information I can tell that the network segment is 192.168.2.1/24.
To scan the network you only need to issue the command
nmap -sP 192.168.2.1/24
Here is the result on my windows machine.
The scan took 9.16 seconds. This is a pretty fast network scan. In 9 seconds I was able to determine I have 12 devices connected, a few iphones, ipad, printer, and other machines.
I am always interested in performance and I wanted to see if my linux machine would do the scan faster. (NOTE: the windows machine is using a 802.11 G network and the linux machine is over the LAN bridge using Wireless G as well)
The Linux results of the same nmap command ran in 5.4 Seconds. In this simple test the linux nmap process was a bit faster.
Overall it is always a great idea to see what and how is around you when on a network. I did not go into more detail but you can always use nmap to do more investigation. I can cover that in a later article.