A firewall is a system designed to prevent unauthorized access to or from a private network (which could be just one machine). Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and allows, proxys, or denies the traffic based on specified security criteria.
There is a nice list of firewalls here.
There are many posts on the forums about different firewall apps and scripts so here they all are condensed into one page - please add your comments about each firewall, especially ease of use and a security check at Shields Up
The Linux kernel itself has very powerful firewall called iptables. Other firewalls are usually just frontends.
See the iptables article for more information.
- Simple stateful firewall HOWTO
- NAT'ing firewall - Share your broadband connection
- man iptables http://unixhelp.ed.ac.uk/CGI/man-cgi?iptables+8
Arno's IPTABLES Firewall Script is a secure firewall for both single and multi-homed machines.
- EASY to configure and highly customizable
- daemon script included
- a filter script that makes your firewall log more readable
- NAT and SNAT
- port forwarding
- ADSL ethernet modems with both static and dynamically assigned IPs
- MAC address filtering
- stealth port scan detection
- DMZ and DMZ-2-LAN forwarding
- protection against SYN/ICMP flooding
- extensive user definable logging with rate limiting to prevent log flooding
- all IP protocols and VPNs such as IPSec
- plugin support to add extra features.
ferm (which stands for "For Easy Rule Making") is a tool to maintain complex firewalls, without having the trouble to rewrite the complex rules over and over again. ferm allows the entire firewall rule set to be stored in a separate file, and to be loaded with one command. The firewall configuration resembles structured programming-like language, which can contain levels and lists.
FireHOL is a language to express firewalling rules, not just a script that produces some kind of a firewall. It makes building even sophisticated firewalls easy - the way you want it.
Firetable is an iptables-based firewall with "human readable" syntax.
gShield is a really simple iptables configuration system. (Nothing to do with gnome) Easy to configure, blocks everything not needed (almost) by default. Controlled by only one configuration file. It gave me all stealth on grc.com
- Easy to configure
- Only one configuration file
- Will give you a iptables configuration, which is the best firewall
- No GUI
The Shoreline Firewall, more commonly known as "Shorewall", is high-level tool for configuring Netfilter. You describe your firewall/gateway requirements using entries in a set of configuration files. Shorewall reads those configuration files and with the help of the iptables utility, Shorewall configures Netfilter to match your requirements. Shorewall can be used on a dedicated firewall system, a multi-function gateway/router/server or on a standalone GNU/Linux system. Shorewall does not use Netfilter's ipchains compatibility mode and can thus take advantage of Netfilter's connection state tracking capabilities.
uruk loads an rc file, which defines network service access policy, and invokes iptables to set up firewall rules implementing this policy.
uruk is not available in any Arch Linux repository.
ufw (uncomplicated firewall) is a simple frontend for iptables and is available in the Template:Codeline repository. For a simple firewall with ssh access, perform the following:
sudo ufw allow ssh/tcp sudo ufw logging on sudo ufw enable
This saves the rules for iptables. Edit your rc.conf to enable ufw at boot (in DEAMONS array).
ufw also has the capability of package provided or custom created application rules via the /etc/ufw/applications.d/ directory. For applications like Samba which utilizes multiple UDP and TCP ports an application rule file makes enabling all ports easy:
sudo vi /etc/ufw/applications.d/samba
[Samba] title=Windows file and printer server for Unix description=Tools to access a server's filespace and printers via SMB ports=137,138/udp|139,445/tcp
Note the "|" is used to separate the UDP ports and the TCP ports. Commas are used to separate the port numbers themselves.
For applications that utilize different ports depending on configuration, like Apache, rule files can contain multiple rule sets.
sudo vi /etc/ufw/applications.d/apache
[Apache] title=Web Server description=A high performance Unix-based HTTP server ports=80/tcp [Apache Secure] title=Web Server (HTTPS) description=A high performance Unix-based HTTP server ports=443/tcp [Apache Full] title=Web Server (HTTP,HTTPS) description=A high performance Unix-based HTTP server ports=80,443/tcp
To list the available application settings use:
sudo ufw app list Available applications: Apache Apache Full Apache Secure Samba
To enable just Apache's HTTPS service:
sudo ufw allow Apache Secure
To enable access to Samba only within your LAN:
sudo ufw allow from 192.168.0.0/24 to any app Samba
Further Documentation and Source Citation: Ubuntu Firewall Help
Vuurmuur Vuurmuur is a powerful firewall manager built on top of iptables. It has a simple and easy to learn configuration that allows both simple and complex configurations. The configuration can be fully configured through an ncurses GUI, which allows secure remote administration through SSH or on the console. Vuurmuur supports traffic shaping, has powerful monitoring features, which allow the administrator to look at the logs, connections and bandwidth usage in realtime.
Firestarter is a good GUI for iptables, it has the ability to use both white and black lists for regulating traffic, it is very simple and easy to use, with good documentation available on their website.
Firestarter has gnome dependencies and is available in AUR.
Guarddog is a really easy to use GUI for configuring iptables. After setting up a basic desktop configuration it passes all Shields Up tests perfectly.
Guarddog requires kdelibs3 and is available in the AUR repository.
To have the firewall settings applied at bootup you must run /etc/rc.firewall from inside /etc/rc.local or something similar.
Gufw is an easy, intuitive, way to manage your Linux firewall. It supports common tasks such as allowing or blocking pre-configured, common p2p, or individual ports port(s), and many others! Gufw is powered by ufw , runs on Ubuntu, and anywhere else Python, GTK, and Ufw are available.
KMyFirewall is KDE3 GUI for iptables.
Firewall editing capabilities are simple enough to use to be suitable for beginners, but also allow for sophisticated tweaking of the firewall settings.
KMyFirewall requires kdelibs3 and is available in AUR.
Firewall Builder is "a GUI firewall configuration and management tool that supports iptables (netfilter), ipfilter, pf, ipfw, Cisco PIX (FWSM, ASA) and Cisco routers extended access lists. [...] The program runs on Linux, FreeBSD, OpenBSD, Windows and Mac OS X and can manage both local and remote firewalls." Source: http://www.fwbuilder.org/