Installing a firewall, Part 1

This article is the first in a three-part series that provides a blueprint for setting up a multifunctional firewall and server. You'll want to do this if you don't want to spend the resources to have one computer act as a Web server, another as a print server, yet another as a firewall, and so on. Whether you're concerned about increasing the security level at your small business or setting up a firewall and IP Masquerading server at home, these articles will show you the steps we took to replace an old server with a multifunction server and firewall. After reading the series, you should be able to configure a functional firewall and server that provides basic Internet services while maintaining a moderate level of security.

We will use the systems we set up for one of our clients as our example configuration. The client shop had a Linux-based GNU system as its main server and firewall. The box was an old 486 running Red Hat 5.2, upgraded from 5.1. Over time, its duties had grown from simply mail service to Web, anonymous FTP, login, and CVS (source code revision control) serving. Two years ago, it was compromised twice -- with minimal damage, but several work days lost in cleanup. Further, the old machine (we'll call it plains.example.com) was too slow for all the services it offered -- and our client wanted to add more.

Security analysis

Before deciding what to do, we performed a simple security needs analysis. Our client is a small software engineering firm with virtually no valuable hardware. Its primary asset is its source code and hence the primary risk is the loss or damage of that source code. The client's second main risk is the amount of time that would be wasted in cleaning up after a break-in: finding backdoors and eliminating them, reinstalling operating systems, analyzing logs, and so on.

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