Not Just for Experts

Your computer lets you see the world, but you don’t want the world to see you. Intruders are becoming more sophisticated, and it isn’t enough anymore to hope they won’t notice your inconspicuous workstation. If you’re connected to the Internet, you’d better be behind some kind of firewall. Firewalls come in many sizes, shapes, prices, and designs. Interestingly enough, what used to be called a firewall is now only one of a wide range of security products. The traditional firewall is a form of router that resides in Layer 3 of the OSI reference model. Layer 3 is the layer of the stack that listens for the Internet Protocol, reads IP addresses, and makes decisions about where to route IP datagrams. A firewall additionally inspects the Layer 4 (TCP or UDP) headers to identify services and evaluate flags.