To be able to load your iptables ruled everytime your Linux system is restarted just follow these commands.
$ sudo iptables
-save > /etc/firewall.conf
Open /etc/network/if-up.d/iptables and add:
iptables-restore < /etc/firewall.conf
Provide executable permission:
$ sudo chmod +x /etc/network/if-up.d/iptable
Now, your iptable rules will be loaded every time your Linux box is booted.
If you need to modify your rules just execute:
$ sudo iptables-save > /etc/firewall.conf