The term firewall has many definitions in the industry. The definition depends on how and to what extent a firewall is used in a network. Generally, a firewall is a network device that, based on a defined network policy, implements access control for a network.

Apart from doing this basic job, firewalls are often used as network address translating devices, because they often tend to sit on the edge of a network and serve as entry points into the network. Figure 7-1 shows the basic philosophy of a firewall setup.

Figure 7-1. Basic Firewall Philosophy

Some important characteristics distinguish a serious, industrial-strength firewall from ...

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