Firewall Rules
Personal firewalls and other small-scale, GUI-based firewall tools usually let you define the firewall’s filtering characteristics by checking boxes (Figure 10.5). But full, industrial-strength firewall tools let you create a configuration file with the firewall configuration expressed in a series of commands or rules defining the firewall’s behavior. These commands or rules are known as firewall rules. Different tools use different commands and syntax, but firewall rules typically let the network administrator create associations consisting of
A source address or address range
A destination address range
A service
An action
Figure 10.5. Most SOHO firewalls let you block services by name or port number.
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