Protected and More Protected
In the diagram on top, the internal network is protected by only one screening router (a router with packet filtering). If there were servers on the internal network providing services to Internet users, this would offer minimal protection against an attack. The use of two screening routers in the firewall configuration at the bottom offers two points of protection from the outside world to the internal LAN.
Elron Firewall was a product that combined stateful inspection, multilayer analysis of IP and IPX packets and network address translation to secure a network. The window on the left could scroll down to more than 70 user services. (Screen example courtesy of Elron Software, acquired in 2003 by Zix Corporation, www.zixcorp.com)
An Excellent Resource
O'Reilly's "Building Internet Firewalls, 2nd Edition" by Zwicky, Cooper and Chapman is one of the best books written on Internet and Web security. It covers a huge range of firewall and related topics and should be a "must have" for anyone interested in the subject. (O'Reilly & Associates, Inc., 2000, ISBN 1-56592-871-7)
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