To save iptables rules :

# sudo iptables-save
# sudo sh -c "iptables-save > /path/to/directory/iptables.rules"

To restore iptables rules :

# sudo sh -c "iptables-restore < /path/to/directory/iptables.rules"

Write the following script in a file /etc/network/if-post-down.d/iptablessave

#!/bin/sh
iptables-save -c > /etc/iptables.rules
if [ -f /etc/iptables.downrules ]; then
iptables-restore < /etc/iptables.downrules
fi
exit 0

Write the following script in a file /etc/network/if-pre-up.d/iptablesload

#!/bin/sh
iptables-restore < /etc/iptables.rules
exit 0

Run the following commands :

# sudo chmod +x /etc/network/if-post-down.d/iptablessave
# sudo chmod +x /etc/network/if-pre-up.d/iptablesload