Managing your Firewall on Ubuntu systems sounds like something important, but there is no default tool installed to do this job. Fortunately, Gufw comes to the rescue.
Linux users are accustomed with secure systems and don't usually run into problems due to not having an active firewall. The beauty of Linux systems is that most of them are open and can be tinkered with, which makes the installation of firewalls and other tools pretty straightforward.
Ubuntu systems, including the latest 14.04 LTS (Trusty Tahr), have a default firewall configuration tool called UFW, which stands for Uncomplicated Firewall. This tool is disabled by default, but it can be easily maintained and configured if you have the time for it. UFW is just a backend, so everything you do must be done in a terminal.
Fortunately, there is also a fronted GUI for UFW called Gufw. Installing it is pretty simple, as the application is already in the official repositories. Keep in mind that the Universe repository is not enabled by default, so you will have to check it before trying to install. You can use either Synaptic or a simple command from a terminal, which looks like this.
sudo apt-get install gufw
Now, the default settings for UFW might be enough for most users, but it's also quite easy to set new rules, if you are so inclined.
“When you turn UFW on, it uses a default set of rules (profile) that should be fine for the average home user. That's at least the goal of the Ubuntu developers. In short, all ‘incoming’ is being denied, with some exceptions to make things easier for home users,” reads the official wiki.
Gufw allows users to access the same command that they would have had to use had they configured UFW from a terminal. This means that the first command to be given is to turn the firewall on.
Users can then apply simple rules, such as Allow, Deny, Reject, and Limit. According to the developers, rules can be configured for TCP and UDP ports, and UFW has some preconfigured programs/services to make setting up rules for them easy.
Also, if all the rules seem to be pretty clear about what they do, the last one, Limit, needs a short explanation. If applied, the Ubuntu system will deny connections if an IP address has attempted to initiate 6 or more connections in the last 30 seconds.
As you can see, configuring the firewall in Ubuntu is simple and anyone can do it. Enjoy!