Ufw
From Kyle's Wiki
Introduction
ufw is the Uncomplicated Firewall that comes with Ubuntu. It allows a quick and easy firewall to be setup.
Quickstart
Status:
ufw status
Enable/Disable
ufw enable ufw disable
Adding Rules based on application:
ufw allow openvpn ufw allow openssh
Adding Rules based on port:
ufw allow 1000/udp
Allowing based on port and interface:
ufw allow in on tap0 to any port 5353 proto udp
IPv6
IPv6 support can be enabled (not on by default) in /etc/default/ufw:
IPV6=yes