Now that the basic components of firewalls have been examined, some examples of different firewall configurations are provided to give a more concrete understanding of firewall implementation. The firewall examples shown here are:
Additionally, a section is provided that discusses methods for integrating dial-in modem access with firewalls. The examples are based loosely on [Ran93], which provides concise but detailed guidance on firewall definition and design. In the examples, assumptions about policy are kept to a minimum, but policy issues that affect the firewall design are pointed out where appropriate. Readers should note that there are many other types of firewalls that are not illustrated here; their absence does not indicate that they are less secure, only that it is impractical to illustrate every potential design. The examples shown here were chosen primarily because they are covered by other literature in more detail and thus serve well as a basis for more study.