Monitoring WiFi devices from the command line
Programming Snapshot – Go WiFi Monitor
© Lead Image © Sergey Nivens, 123RF.com
To see when clients are joining and leaving the wireless network, Mike Schilli writes a command-line utility that uses an object-relational mapping interface to store metrics in SQLite to later display historical data.
"What I don't know won't hurt me," as the saying goes, but the reverse is true for my wireless network. What are all my household gadgets doing? After all, no newly released device seems to be able to manage without a wireless network connection nowadays. Or are there actually some devices that I don't even know about? This definitely worries me and keeps me tossing and turning in my sleep.
On top of that, I am interested in more than the current situation. Curious by nature, I would like to know how long a device, once discovered, has been operating on the network, when it joined the network, and whether it is permanently active or occasionally lets its assigned IP address lease expire and then picks up a new one later. Let's build a data logger in Go to find out.
To detect active devices on the wireless network, it makes sense to call up the nmap scanner. This hacking tool is included with every good Linux distribution and knocks on the door of all potentially usable IP addresses in a subnet to see if a host responds. On a typical 192.168.0.0/24 subnet of a router for home network use, you can use 255 IP addresses, and nmap scans them with a barrage of probes at lightning speed (Figure 1).
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