How to identify the local network you are connected to

Question

I need a script to be able to identify if the computer is connected to my home network, to my work network, o to a different network, either by wifi or by cable.

My question is if there some network identifier available and how to get it from within a shell script.

Answer 1

Your home, work, and so on are distinguished by different public IPs, so that you can use any CLI command that returns your public IP address and act upon the outcome of such commands.

Any of these commands will work on a normal Linux distro, I am certain wget exists in Cygwin, I simply do not know about curl and lynx:

wget -q -O - ipecho.net/plain
curl ipecho.net/plain
lynx --dump ipecho.net/plain

Acting on your public address has the added bonus that you can distinguish a different LAN using the same subnet as your work/home/whatnot from your work/home/..., should you ever bring your laptop to a new place.

Answer 2

If there is a simple command to do this, I am not aware of it. What might work is the following:

wireless=<put name of wireless card here, e.g. wlp2s0>
wired=<put name of wired network adapter here, e.g. p1p1>
dev=$(ip route | grep default | awk '{print$5}') #finds the device that your Internet is coming through
if [ x$dev = x$wired ]; then
    echo "Wired connection."
elif [ x$dev = x$wireless ]; then
    echo -n "Wireless connection: "
    iwconfig $wireless 2>&1 | grep ESSID | sed 's@.*ESSID:\"\(.*\)".*@\1@' # prints ESSID of wireless connection only
fi

That should work, as long as you don't forget to fill out the wired/wireless variables.

EDIT You definitely SHOULD say that you are running cygwin under Windows. This script most likely won't work under cygwin. I have never used cygwin so I don't know the level at which it imitates Linux. If this script doesn't work, you are out of luck (I think).

Answer 3

Are the subnet masks different based upon which network you connect to? Your home will be 255.255.255.0 while your work will VLSM out at 255.255.255.254 or less.

Check via command line in Windows with ipconfig and check the subnet mask with ifconfig for Linux.

Another way to tell would be to DNS resolve from your computer and see what DNS picks it up, is it your ISP that you use at home or the DNS servers under your offices domain? That would also tell you, i mean a look at your routing tables also.

Check this out and see if you first routes are from inside your companies domain, run this from within command prompt. Find command prompt and open it and type:

netstat -f

 TCP    10.0.0.145:56433       stackoverflow.com:http  ESTABLISHED  
 TCP    10.0.0.145:56462       stackoverflow.com:http  ESTABLISHED   
 TCP    10.0.0.145:56592       stackoverflow.com:http  ESTABLISHED
 TCP    10.0.0.145:56748       stackoverflow.com:http  ESTABLISHED
 TCP    10.0.0.145:56782       stackoverflow.com:http  ESTABLISHED
 TCP    10.0.0.145:56902       stackoverflow.com:http  ESTABLISHED
 TCP    10.0.0.145:56949       stackoverflow.com:http  ESTABLISHED
 TCP    10.0.0.145:57056       stackoverflow.com:http  ESTABLISHED

Example above shows where we are now, the IP's are resolved because of our -f to this site it should be. Someone said you are running Cygwin in the Windows environment. Why don't you just add the "cygwin\bin" directory to your windows path? You'll have full access to most GNU tools, and can use them in pretty much the same way you do on Linux.