You may wish to configure a firewall to protect your computer from
unauthorized access.

Understanding a few basic concepts will help you configure a firewall
and should be sufficient for most desktop users.

First, keep in mind Linux, and thus Ubuntu, is modular. This means that
rather then one large program that "does it all" , several smaller
applications are used. Often there is more then one option for each
individual component.


Firewall

The firewall is called netfilter and by default is permissive, meaning
it allows all traffic. netfilter can be configured using a command line
program iptables.


Configuration Tools.

There are several tools that can be used to configure a firewall.

UFW is a command line tool included with Ubuntu. To activate your
firewall open a terminal and type

[code]sudo ufw enable[/code]

For the vast majority of desktop users ufw is sufficient.

Many people prefer graphical configuration tools and the default
graphical tool in Ubuntu is gufw. It can be installed using Add/Remove
programs, synaptic, or command line tools and is available from your
menu under

System -> Administration -> Firewall Configuration.

To active your firewall , click (check off) the "Enabled" button on the
Left, under "Actual Status".

If you prefer, several additional configuration tools are available in
the Ubuntu repositories including Firestarter, Guard dog, and Shorewall.


Testing and Monitoring your network traffic (firewall).

Because Ubuntu is modular we have separate options to test and monitor
network traffic.

To test your firewall it is best to scan it from a second computer and
nmap is a popular application to use. Again you will need to install
nmap , then run

[code]nmap -vAPN ip_address[/code]

To see what services are associated with the open ports run

[code]lsof -i -n -P[/code]

Actual monitoring of your network traffic can be done with either
wireshark or snort. Wireshark will analyze the network packets (of
information) and snort is used in NIDS (Network Intrusion Detection
System) and will notify you of unusual traffic.

-- 
Firewall documentation is outdated
https://bugs.launchpad.net/bugs/377039
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