Monitors your public IP address and removes your default gateway if it doesn't like what it finds

Monitor-PublicIP.sh

#!/bin/bash

ADDRESS="69.65.44.96"  # default for my public IP now
PAUSE=1  # default to 1 second for now

# Get command line arguments
# Use -gt 1 to consume two arguments per pass in the loop (e.g. each
# argument has a corresponding value to go with it).
# Use -gt 0 to consume one or more arguments per pass in the loop (e.g.
# some arguments don't have a corresponding value to go with it).
while [[ $# -gt 1 ]]; do
	key="$1"

	case $key in
		-a|--address)
			ADDRESS="$2"
			shift  # past argument
			;;
    	-p|--pause)
    		PAUSE="$2"
    		shift  # past argument
    		;;
    	--default)  # not used in this script
    		DEFAULT=YES
    		;;
    	*)
        	# unknown option
    		;;
	esac
	
	shift  # past argument or value
	done

echo "Public address for VPN: $ADDRESS"
echo "Pause between address checks: $PAUSE seconds"

# Get our current Default Gateway from /sbin/route and save it
gateway="$(sudo /sbin/route -n | awk '{if ($1=="0.0.0.0") {print $2} ; q}')"
echo "$gateway" > default_gateway

# Checking that we are still accessing the internet through the VPN
while true; do
	# retrieve what our public IP address is
	publicIP="$(wget http://ipinfo.io/ip -qO -)"

	# If we can't reach the above web page to retrieve out public IP
	if [ -z $publicIP ]; then
		echo "Failed to retrieve public address"
		sleep 60

	# does this IP match what we would expect through the VPN? 
	elif [ $publicIP != $ADDRESS ]; then
		echo "Public address found: $publicIP"
		echo "Removing Default Gateway"

		# If not, then we need to pull the Default Gateway
		# This is just the quick and dirty to kill the traffic out of the LAN 
		sudo /sbin/route del default gw "$(cat default_gateway)"
	
	fi

	# pause between iterations so we aren't needlessly spamming
	sleep $PAUSE
	done