In Chapter 1, we discussed, in general terms, what you're trying to protect when you connect to the Internet: your data, your resources, and your reputation. In designing an Internet firewall, your concerns are more specific: what you need to protect are those services you're going to use or provide over the Internet.
There are a number of standard Internet services that users want and that most sites try to support. There are important reasons to use these services; indeed, without them, there is little reason to be connected to the Internet at all. But there are also potential security problems with each of them.
What services do you want to support at your site? Which ones can you support securely? Every site is different. Every site has its own security policy and its own working environment. For example, do all your users need electronic mail? Do they all need to transfer files to sites outside your organization? How about downloading files from sites outside the organization's own network? What information do you need to make available to the public on the Web? What sort of control do you want over web browsing from within your site? Who should be able to log in remotely from another location over the Internet?
This chapter briefly summarizes the major Internet services your users may be interested in using. It provides only a high-level summary (details are given in later chapters). None of these services are really secure; each one has its own ...