Creating A Linux Firewall Using the TIS Firewall Toolkit

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If you have a valuable or fragile network to protect, you may want to protect it with a very strong, well-proven firewall. In this article, Benjamin Ewy explains very thoroughly how to build your own 'bastion host' firewall with Linux.
Final Points and Additional Resources

The TIS Firewall Toolkit is a very flexible and useful collection of programs for creating bastion hosts. A collection of examples of how to configure a Linux-based bastion host have been presented. Many of these programs have additional features, and the documentation that comes with the toolkit should be read to get the most out of these programs. Several additional tools, such as a portscanner and several log summary generators, come with the fwtk.

One final step before completing your bastion host is the removing of any unnecessary programs that may have been installed. In general, new holes are found every day, so the fewer programs installed, the better. This includes gcc! Without a compiler, many hackers are limited in what they can do if they should break in. It is a good idea to run Tripwire on your system after it is configured, to provide a safeguard against unauthorized modifications to the system. Tripwire verifies the checksums of files and alerts you to modifications. Finally, make a complete backup of your bastion host so that you have a “Day 1” copy to revert to in case of emergency.

There are many useful references for information on firewalls. The fwtk comes with an overview, an installation and configuration guide, a user manual that shows users how to access services through the firewall, and man pages for all of the programs associated with the fwtk.

Useful Linux resources include the Linux NET-2 HOWTO, the Linux Firewall HOWTO, the Linux Multiple Ethernet mini-HOWTO, and the Linux Kernel HOWTO. All of these are available on sunsite.unc.edu, tsx-11.mit.edu, and their mirrors.

These and other useful online information about firewalls can be found at TIS Resources.

Several excellent books on firewalls are:

  • Firewalls and Internet Security. Cheswick & Bellovin, Addison Wesley.

  • Building Internet Firewalls. Chapman & Zwicky, O'Reilly & Associates.

  • Internet Firewalls and Network Security. Siyan & Hare, New Riders Publishing.

Benjamin Ewy (bewy@tisl.ukans.edu) has been involved in Unix system administration for 5 years and has used Linux professionally for 3 years. His professional interests include all aspects of network engineering, particularly network security. When not working, he enjoys designing loudspeakers and spending time with his new family.

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