ABSTRACT
Many companies protect their networks from unauthorized access by implementing a security program using perimeter protection devices, including the screening router and the secure gateway. A screening router is a network device that offers the standard network routing services, and incorporates filters or access control lists to limit the type of traffic that can pass through the router. A firewall or secure gateway is a computer that runs specialized software to limit the traffic that can pass through the gateway. (The term “secure gateway” is used here rather than the more generic term “firewall.”)
Although on the surface they seem like they are doing the same thing, and in some respects they are, the router and the secure gateway operate at different levels. The screening router and the secure gateway both offer services that protect entry into the protected network. Their combined operation establishes the firewall as shown in Exhibit 131.1.
