Firewall Insertion in the Network Topology

To enforce access control policies between domains of trust, firewalls first need to be inserted into the network topology. The following sections examine the two basic forms of promoting this insertion: Routed mode and Transparent mode.

Routed Mode Versus Transparent Mode

Although a firewall can be simultaneously connected to multiple domains (with possibly many interfaces within each domain), two interfaces are usually sufficient for the analysis of the main concepts. Figure 1-4 depicts the two basic forms of connecting firewalls to network environments: