@SeUbHS
Hello!
Yes, set your blocking rules as default rules while Eddie is not running and has just exited cleanly. Remember to allow local network, and special destinations such as 255.255.255.255 in order not to block DHCP (at bootstrap etc.). Since you run iptables you can simply enforce DROP policy to the OUTPUT and INPUT chains of the filter table, and then set a few rules jumping to ACCEPT for local subnet, localhost and 255.255.255.255.
A very simple startup script (it's only an example, you must modify it according to your needs and the features of your network, and you can also use iptables-save to make rules permanent - also specify the correct path to iptables):
iptables -F
iptables -P OUTPUT DROP
iptables -P INPUT DROP
iptables -P FORWARD ACCEPT
iptables -I INPUT -s 255.255.255.255 -j ACCEPT
iptables -I OUTPUT -d 255.255.255.255 -j ACCEPT
iptables -I OUTPUT -s 192.168.0.0/16 -d 192.168.0.0/16 -j ACCEPT
iptables -I INPUT -s 192.168.0.0/16 -d 192.168.0.0/16 -j ACCEPT
iptables -I INPUT -s 127.0.0.1 -d 127.0.0.1 -j ACCEPT
iptables -I OUTPUT -s 127.0.0.1 -d 127.0.0.1 -j ACCEPT
When Eddie enables Network Lock, you can communicate with AirVPN infrastructure only. When Eddie disables Network Lock (including when it quits) it will restore your blocking rule, so your machine will be isolated from the Internet.
Kind regards