Notes
How to limit access to MySQL to a sub-network
$ sudo -s
# iptables -A INPUT -p tcp -s 192.168.0.0/32 --dport 3306 -j ACCEPT
# iptables -A INPUT -p tcp --dport 3306 -j DROP
# exit
$ sudo -s
# iptables -A INPUT -p tcp -s 192.168.0.0/32 --dport 3306 -j ACCEPT
# iptables -A INPUT -p tcp --dport 3306 -j DROP
# exit