To load my firewall rules I have always used a init script containing all my iptables rules.
However with the switch to systemd in Debian Jessie things have changed a bit.
create a service file in /etc/systemd/system. In my case this is /etc/systemd/system/firewall.service
[Unit] Description=Firewall [Service] Type=oneshot ExecStart=/bin/sh /scripts/firewall.sh start ExecStop=/bin/sh /scripts/firewall.sh stop ExecReload=/bin/sh /scripts/firewall.sh restart RemainAfterExit=yes [Install] WantedBy=multi-user.target
Important here are the Type and RemainAfterExit parameters. Also don’t forget /bin/sh or /bin/bash if you are executing a script !
Next enable and start the service
systemctl enable firewall.service service firewall start